THE RADIO BUILDER

Morse Code Chart in a geometric Sense

2010-12-28T17:24:00.000-08:00

I like the idea of this chart because it make some sense!
You can her the whole alphabet of morse as midi file (download it first).

download

Source: http://9w2pju.hamradio.my/2009/09/morse-code-chart.html

LEARN MORSE CODE in one minute !
This is a code listening tool. Print it on your printer.
Place your pencil where it says START and listen to morse code.
Move down and to the right every time you hear a DIT (a dot).
Move down and to the left every time you hear a DAH (a dash).
Here's an example: You hear DAH DIT DIT which is a dash then dot then dot.
You start at START and hear a DAH then move down and left to the T and then you hear a DIT so you move down and RIGHT to the N and then you hear another DIT so you move DOWN and RIGHT again and land on the D
You then write down the letter D on your code copy paper and jump back to START waiting for your next letter.
The key to learning the code is hearing it and comprehending it while you hear it.
The only way to get there is to practice 10 minutes a day.
Listen to code tapes or computer practice code while tracing out this chart and you will find yourself writing down the letters in no time at all without the aid of the chart.
The chart brings repetition together with recognition, which you don't get from any other type of code practice aid.

HEAR slow morse code This code speed is slow enough to follow the chart above.

LEARN the DITs and DAHs with these MP3 files:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1 2 3 4 5 6 7 8 9 0

And the character to emphasize that there she was, she was walking down the street, is :
do-wah-diddy-diddy-dum-diddy-do

Goto DOWNLOADS page for hours of MP3 code practice
email KB3BYT

HOW TO LEARN MORSE CODE AND ENJOY IT

FOX HUNTING ANTENNA PLANS

source: http://www.learnmorsecode.com/

This introduction is my best to the subject:

How to learn morse code. And enjoy it.
Morse code is not a chore. Its a challenge.
Its a challenge of your ability to learn a new language.
And it is truly a language.
There are millions of people who successfully learn a foreign language
so you can be certain that its not so farfetched to think that you too may learn a new language.
The secret to learning a language is to jump into the pool, over your head, totally emerse yourself in your new language.
If you want to speak Chinese then the best way to learn Chinese is to go to China and only hear Chinese.
We all can't do that.
But we can come real close with today's recording technologies with cassette tapes and DVD and CD and MP3 recordings.
Morse code is the same. Listen to it. All the time. It doesn't matter if its just slow or just fast.
It doesn't matter if you do not understand a single word at first.
There are a dozen methods to practice and get your brain to retain what the letters are.
Practice reinforces and recognition will come with practice.
Then... one day ... you start hearing entire words and sentences that make sense..at speeds that
you never dreamed you would understand.
Some peple say that you should never use a chart or any visual aid to learn morse code.
All people are created a bit different and what works for some people , does not always work for everyone else.
So don't try just one method to learn morse code. Try a few and decide what works best for you.
This chart at http://www.learnmorsecode.com is just one of many methods to learn morse code.
This particular method will work for all ages to immediately put together the noise of morse code with the meaning
of the noise. It does not matter if it is a slow process. All that matters is that your brain gets a chance to connect the dots and make some meaning out of it all.
Many people give up trying to learn morse code beacuse they do not ever get the noise to stick in their brain and recognise what letter they just heard.
This method will sew together that recognition if you practice this method for 10 minutes every day with the
SLOW code A-Z file.
After you no longer need the chart...then...and only then....move on to the faster code practice download files.
There are computer programs that can make morse code to teach you.
I like the software at http://www.g4fon.net/
I highly recommend you use that software to learn the letters and also to make your own practice audio files.
If you can not make a computer do recordings and carry around MP3 files
then use cassette tapes. They are cheap to make and WALLMART sells casette players for $5.00 now.
The computer programs that generate practice morse code are great
and FREE so have fun with it.
One method to learn morse code is called CODE QUICK.
CODE QUICK has you listen to a letter and associate small sentences with the sounds
of the morse code. An example of this method is to hear the letter K in morse code
which is made up of the sounds DAH DIT DAH.
You hear the DAH DIT DAH and it actually sounds like KANG ga ROOOOO.
So your brain hears the DAH DIT DAH and injects KANGAROO into your minds eye
and you say AH HAA!!!! KANGAROO begins with a K so what I just heard was a K !!!!!
You write down the K and along comes the next letter.
There are SOUND ALIKES for every letter of the alphabet and numbers too.
You are encouraged to make up your own sound alikes for the
letters if you have trouble using the CODE QUICK sound alikes.
CODE QUICK taught me morse code at a time where no other method worked for me.
I did not learn about the LEARNMORSECODE.COM chart until years after I used CODE QUICK.
You can BUY code quick at http://www.cq2k.com for around $30.
The methods used at code quick are very straight forward and actually have been around
for many many years before the code quick author published the first code quick
casette tapes and work book course.
I have an uncle that was a code listener during the Vietnam war and one day he visited
me during a morse code contest and very fast morse code was playing on my radio and it
was was too fast for me to understand and my uncle sat down next to me and asked me what I
was doing and I told him I was trying to understand the hailing station but I was too new at
it to understand.
My uncle told me what the station was saying and then told me about his code listening days
so I asked him to respond and he told me that he never sent a single dit in all those years.
All they did was spy on the enemy.
He understood the fastest of the code so I asked my uncle to explain to me the method that
the army used to teach him the code in 1965 and he told me that the army made them memorise little
phrases like a baby crying wants his mother to give him a drink of water and
that sounds like MaWAWA and is the letter W ...DIT DAH DAH.
That just blew my mind because that was precisely what CODE QUICK used to remember W also.
This man was a high speed spy listener that got his first morse code training with this learning method.
So this method truly works but you will have your sticks in the mud old farts telling you
that CODE QUICK sound alikes will only slow you down from learning truly high speed morse code at 20 words per minute.
Well to hell with sticks in the mud.
If you learn morse code at 5 words per minute using sound alikes and have fun with listening
to any morse code then moving up to high speed code will be another challenge and practice
is what makes perfect.
You will find that if you know 5 words per minute slow speed morse code and you listen to
ramp recordings where the letters are played slow at first and then ramp up to real fast
code of the same letters, the ramped up speed will stick to your brain quite
well because you already knew what the slow letters sounded like and you will enjoy the
comprehension instead of being all wrapped up in being lost in fast practice code.

So thats my 2 cents on learning morse code.
Have fun.
from Rob KB3BYT
source: http://www.learnmorsecode.com/

Airband_VHF_1T_Regen_High gain audio amp required

2010-12-19T19:37:00.000-08:00

Parts:
R1, R3    =    47K 1/4W Resistor
R2    =    10K 1/4W Resistor
R4    =    4.7K 1/4W Resistor
R5    =    5K Linear Taper Pot
R6    =    2.2K 1/4W Resistor

C1, C2 =       0.001uF Ceramic Disc Capacitor
C3, C6    =    0.001uF Ceramic Disc Capacitor

C4    =    2.2pF Ceramic Disc Capacitor
C5    =    1pF Ceramic Disc Capacitor
C7    =    15uF 15V Electrolytic Capacitor
C8    =    18pF Variable Capacitor
D1    =    1N82 Diode
Q1    =    2N918 NPN Transistor
L1    =    See Notes
L2    =    1.8uH Inductor
ANT1    =    Approx. 18 Inch Wire Antenna
MISC    =    PC Board, Wire, Knob For C8

The communications between commercial aircraft and the ground can be interesting, amusing and sometimes even disturbing. However radios that receive the approximately 220MHz to 400MHz band commonly used for aircraft (both military and commercial) are not easily found. And scanners can be complicated, large and expensive. With an easy to build circuit such as this one, everyone can enjoy listening in on these conversations.

# The circuit originally appeared in the Think Tank column of the Sept. 1995 issue of Popular Electronics.

# L1 is made by winding 2 turns of 22 AWG magnet wire on a 5/32 drill bit. This inductor can be modified to shift the frequency range of the circuit.

# The antenna can also be placed at the anode of D1 if overload is a problem with it connected to the emitter of Q1

# R5 adjusts regen and thus sensitivity.

Source: http://www.project-world.co.cc/links/schematics/radios/ABS.html

MW_3T_Reflexive

2010-12-18T16:47:00.000-08:00

Meter_Voltmeter

2010-12-18T16:45:00.001-08:00

MW_3T_1D_Reflexive

2010-12-18T16:43:00.001-08:00

MW_3T_Reflexive

2010-12-18T16:41:00.001-08:00

MW_LW_4T_Reflexive

2010-12-18T16:39:00.001-08:00

MW_1T_Reflexive_High gain audio amp. required

2010-12-18T16:33:00.000-08:00

SW_2T_Reflexive

2010-12-18T16:31:00.000-08:00

Meter_Bipolar Beta Meter

2010-12-18T16:28:00.001-08:00

MW_2T_1D

2010-12-18T16:26:00.000-08:00

Meter_Audio Frec. Inductance Capacitance Meter

2010-12-18T16:23:00.000-08:00

Equivalents of Russian Transistors

2010-09-23T21:55:00.000-07:00

1. Bipolar transistors
Russian part	Short description	Western analog
KT3102A	general use n-p-n silicon transistor	BCY43, BC107A, BC170, BC207A, 2N4123, MPS3709
KT3102E	npn silicon transistors with high h21e (>600)	2N5210, for example
KT312A-B	general use n-p-n silicon transistor	Almost the same as KT315, excluding case type.
KT608A	HF middle-power silicon n-p-n transistor	BSX21, 2SC796
KT606A-B	middle-power silicon n-p-n transistor for use on HF and VHF applications	Couldn't find, sorry
KT326	Common general-use p-n-p silicon device. I guess, any appropriate western transistor will be able to replace it.	I wonder, why i can't find it in my databases...
KT602B	rather old n-p-n silicon transistor, specially designed for working in final stages of wideband amplifiers.	BSY71
GT308	Very old general-use p-n-p germanium transistor.	Can't find, sorry.
GT311	Old, but still good germanium n-p-n device for working with frequencies up to 800 MHz.	Can't find, sorry.
KT315	general use n-p-n silicon transistor, an old design	BC146,
GT402	low-frequency germanium p-n-p transistor, old design	Do not know*
GT404	complementary pair for GT402	Do not know*
MP25A-B	Very old p-n-p transistor for 'draft' purposes	ACY19, ACY23, 2N190-191
KT503A	general use n-p-n silicon transistor (for rather low frequencies)	2SD762, for example
P214A	Very old p-n-p high-power transistor for low frequencies	AD142, for example
KT368A-B	Very good high-frequency n-p-n transistor with low noise factor	BFS17 , 2SC252
KT812A	high-power transistor for low frequencies (n-p-n)	KU601, KU602
KT815	Middle-power n-p-n silicon transistor for use in low-frequency circuits	BD165
KT814	Complementary pair (p-n-p) for KT815	BD170
KT818G	High-power p-n-p transistor, widely used in power supplies and output stages of AF amplifiers.	AD142
KT819G	The same as KT 818G, but with n-p-n structure	BDY20, BDY23
KT940A	high-voltage transistor for final stages of video-amplifiers in TV	BF338

* - I suppose, any general use germanium transistor will work instead.

2. Field-effect transistors
Russian part	Short description	Western analog
KP303A	n-channel JFET with rather low amplification	haven't found*
KP307B	n-channel JFET, general use	2N3819
KP302A	the same as above	haven't found*
KP303E	the same as above	MPF102
KP350A	two-gate n-channel MOSFET transistor	2SK39

* Though I haven't found a direct equivalent for this device in my databases, it seems to me,that they are replaceable to 2N3819 and other general-use JFETs (may be, with a slight correction of DC conditions)

3. Analog and digital integrated circuits
Russian part	Short description	Western analog
K544UD1	General-use operational amplifier with high input impedance	CA740
K155LA3	four TTL 2&-not elements	SN7400
K155LA12	the same as LA3, but with more powerful outputs	SN7437
K155IE2	Asynchronous TTL counter.. Has two counters inside - one counts up to 2, the second - up to 5. They may be used separately or connected in series forming a decade.	SN7490
K155TM2	Two dynamical TTL triggers of 'D'-type. Also has external 'set' and 'reset' inputs.	SN7474
K155TM7	Four TTL triggers of 'D'-type. Ideal for using as a 4-bit storage device	SN7475
K155ID6	A simple 4 -> 10 decoder	SN7442
K514ID2	4 -> 7 decoder with blanking input for a 7-segment indicator (LED, for example)	MSD101
K500LP116	Three differential ECL receivers/amplifiers	MC10116
K500TM131	Two ECL D-triggers	MC10131

Valentin Gvozdev, Moscow

Source: http://matthieu.benoit.free.fr/cross/russian_equiv.htm

MW_TRF Good Radio_1T_1IC_2Diodes

2010-09-22T23:53:00.000-07:00

Here's a very simple AM Radio circuit I've designed couple of years ago. Don't know whether anybody listen to AM stations anymore. But I still use it(maybe I wanted to listen to my own built radio lol..). The radio section is wired using a single transistor(BF494) and it was so amazing that an audible sound is recovered at the output which is faint though. It doesn't use any external antenna and the sensitivity/selectivity of the receiver is pretty good. However I used an amplifier(TA 7368P Toshiba, Low voltage) which drives an 8ohm/1W 4" speaker inside a box rocks the entire room with a high fidelity audio that is unbelievable and outperforms Superheterodyne ones in this regard . It is a reflex receiver.

The audio recovered at inductor L is rather strong comparing to ZN414 and free from oscillations.(I've never succeeded in building ZN414 which always give me annoying motorboating and chirping crappy I say!)

Using a flat ferrite bar antenna allows local reception for a pocket radio and a big rod antenna captures stations beyond 200miles! So it doesn't require an external wire antenna, adding it only helps in electrical noise catch.

Only critical part in the circuit is inductor L, its optimum value gives excellent results. Make rf parts close to the transistor. I made it on a 1.5" ultra small pcb. 2 x AA battery lasts very long.

Another important thing is that the radio is absolutely silent in between the stations - means no noise at all if no any electrical interferance which is a plus point over Superheterodyne receivers. It was so amazing to tune it during power failure period. So I'll call it a true radio.

Source: http://www.electro-tech-online.com/electronic-projects/94129-simple-am-radio-receiver.html

Suggestion: Replace the upper diode by a Germanium one for more sensitivity.

Theory_Reflexive Circuit and pre-Amplifier

2010-09-20T23:10:00.001-07:00

Theory_How to modify the coupling

2010-09-20T23:07:00.000-07:00

MW_Superhet_3T

2010-09-20T23:05:00.001-07:00

Valve Sensitive Amplifier_1V_1T

2010-09-20T23:03:00.001-07:00

Theory_Using NPN Transistor in Class A Amplifiers

2010-09-20T22:59:00.001-07:00

MW_2V_2T_Valve Transistor Hybrid Receiver

2010-09-20T22:57:00.000-07:00

MW_Reflex_4T_Spontaflex Radio by Sir Douglas

2010-09-20T22:54:00.001-07:00

MW_1V_One Valve Reflexive Radio

2010-09-20T22:52:00.001-07:00

MW_2V_Two Pentude Valvees Radio

2010-09-20T22:50:00.001-07:00

MW_Reflex_3T

2010-09-20T22:48:00.001-07:00

MW_Reflex_3T

2010-09-18T00:07:00.001-07:00

MW_1V_1T

2010-09-18T00:05:00.001-07:00

MW_1V_1T

2010-09-18T00:02:00.001-07:00

MW_Reflex_3T_Six Stage_Genious Circuit

2010-09-18T00:00:00.001-07:00

Several Reflex Circuits

2010-09-17T23:53:00.001-07:00

Simple Antenna Theory for HAM

2010-09-16T20:07:00.000-07:00

James R. Duffey KK6MC/5
(a.k.a. Dr. Megacycle) - reproduced with permission

Subject: [Antennas] Some Rules of Thumb for Beginners
Date: Sun, 20 Feb 2000 16:44:19 -0700
From: "James R. Duffey"
To: "Low Power Amateur Radio Discussion"
Every now and then somebody asks the list for antenna suggestions. Quite often these people asking are beginners who are afraid of making the wrong choice. In order to help QRPers choose antennas wisely I have compiled a few "rules of thumb". As with any rules of thumb, these are general and there are some exceptions to them. A few may be somewhat controversial and I am sure alternate views will be given by those with opposite views. However I intend these guidelines to point one in the right direction rather than providing a detailed map of what to do.
1. Any antenna is better than no antenna. Rather than agonizing over an antenna choice, just put one up and operate. After operating with it for a while you will become aware of your operating habits and the shortcomings of the antenna you have erected. That will give you some hints as to which direction you should go with another antenna. You can lose 1/2 of your power in poor antenna system efficiency and only be down an S unit or so. I hear lots of S9 QRP stations. They would still make fine QSOs at S8. I am not advocating antenna inefficiency, but you can live with it. It is better than no antenna at all.
2. Higher antennas generally out perform lower antennas. A vertical on the roof of a one story house is probably a better choice than one on the ground in the backyard. A dipole whose end is tied to a 5 or 10 ft mast on top of the house will out perform one whose end is merely fastened to the eaves.
3. Most people will be happier with a low dipole than with a vertical. Verticals require a bit more attention to work effectively and beginners can become frustrated in dealing with ground issues.
4. It pretty much doesn't matter what kind of copper wire you use in an antenna. Thick or thin, insulated or bare, stranded or solid, they will all perform fairly well. Any effects due to these characteristics will be "second order". The old formula for cutting a half wave dipole, 468 / frequency (in Mhz), may be a bit different for various combinations, but this formula is only an approximation anyway.
5. Whatever antenna you chose, if it is fed with coaxial cable you should use a choke balun. This will prevent the feed line from becoming part of the antenna which can cause all sorts of problems. There are many designs to chose from. My favourite is an air core balun wound from coax. These are described in the The ARRL Handbook for Radio Amateurs 2010 and in the ARRL Antenna Book. You don't have either?
Then:
6. Purchase a Handbook or ARRL Antenna Book and study it. Antennas don't change much, so even an old copy of the Antenna Book will be very useful. These show up at Ham Fests occasionally. You can also special order ARRL publications from good bookstores.
7. Outdoor antennas perform better than indoor ones. If all you can erect is an indoor antenna, fine, but try to see if there is a way to get up an antenna outside. A thin wire supported an inch or more away from the building will be much better than one inside. If you can dangle a wire out a second story window, feed against a counterpoise, that will be a pretty good antenna.
8. Don't scrimp on feed line. Good, low-loss feed line does not cost much more than the antenna it is feeding.
9. Most single band antennas can be made into multiband antennas by feeding them with a balanced feeder like window line and using a tuner. This applies to loops as well as dipoles. For an inexpensive low loss tuner see Cecil's method of changing the feed line length to achieve a match:

http://www.w5dxp.com/notuner.htm >

10. If you have antenna restrictions consider a temporary antenna. The SD-20 Blackwidow Crappie Pole can be erected with a wire of choice to make a vertical in a matter of seconds. With a few radials or a chain link fence as a ground, this can give a good account of itself. If somebody complains about it take it down and next time erect it where they can't see it.
11. Consider your operating practices in choosing an antenna. If you can only operate in the evening, then even a high 10 M antenna will not provide you with much operating time. The band will usually be dead after sunset. On the other hand, a 40 M dipole will provide you with a number of contacts late into most evenings. It can also be used on 15 M for those occasions when you can operate during the day.
12. Avoid the temptation to "have it all". Multiband antennas are often attractive to new comers. So are electrically "small" antennas. They are by necessity compromises, and usually don't work as well as single band antennas. I suggest erecting a single band dipole and using it for a while. As you get used to operating or have desires to try out other bands you can erect another antenna, or feed the one you have (if it is a dipole) with ladder line for multiband use. You can build and feed a lot of single band dipoles for the price of an R-7000!!
13. Home-made antennas are better than commercial ones. Ask anyone on the list who has built one!!
I hope that someone finds this useful. See you on the air. - Dr. Megacycle KK6MC/5

James R. Duffey KK6MC/5

Source: http://my.integritynet.com.au/purdic/antennas-rules.htm

What is Superhet?

2010-09-16T20:05:00.000-07:00

What are the basics of a superhetrodyne radio receiver?

A superhetrodyne receiver works on the principle the receiver has a local oscillator called a variable frequency oscillator or V.F.O. which maintains a constant difference between itself and the received frequency resulting in a constant intermediate frequency

This is a bit like having a little transmitter located within the receiver. Now if we still have our T.R.F. stages but then mix the received signal with our v.f.o. we get two other signals. (V.F.O. + R.F) and (V.F.O. - R.F).

In a traditional a.m. radio where the received signal is in the range 540 Khz to 1650 Khz the v.f.o. signal is always a constant 455 Khz higher or 995 Khz to 2105 Khz.

Several advantages arise from this and we will use our earlier example of the signal of 540 Khz:

(a) The input signal stages tune to 540 Khz. The adjacent channels do not matter so much now because the only signal to discriminate against is called the i.f. image. At 540 Khz the v.f.o. is at 995 Khz giving the constant difference of 455 Khz which is called the IF frequency. However a received frequency of v.f.o. + i.f. will also result in an i.f. frequency, i.e. 995 Khz + 455 Khz or 1450 Khz, which is called the i.f. image.

Put another way, if a signal exists at 1450 Khz and mixed with the vfo of 995 Khz we still get an i.f. of 1450 - 995 = 455 Khz. Double signal reception. Any reasonable tuned circuit designed for 540 Khz should be able to reject signals at 1450 Khz. And that is now the sole purpose of the r.f. input stage.

(b) At all times we will finish up with an i.f. signal of 455 Khz. It is relatively easy to design stages to give constant amplification, reasonable bandwidth and reasonable shape factor at this one constant frequency. Radio design became somewhat simplified but of course not without its associated problems.

Source: http://www.electronics-tutorials.com/receivers/superhetrodyne-radio-receivers.htm

What is TRF?

2010-09-16T20:04:00.000-07:00

What is a tuned radio frequency TRF receiver?

The T.R.F. (tuned radio frequency) receiver was among the first designs available in the early days when means of amplification by valves became available. The basic principle was that all r.f. stages simultaneously tuned to the received frequency before detection and subsequent amplification of the audio signal.

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The principle disadvantages were (a) all r.f. stages had to track one another and this is quite difficult to achieve technically, also (b) because of design considerations, the received bandwidth increases with frequency. As an example - if the circuit design Q was 55 at 550 Khz the received bandwidth would be 550 / 55 or 10 Khz and that was largely satisfactory. However at the other end of the a.m. band 1650 Khz, the received bandwidth was still 1650 / 55 or 30 Khz. Finally a further disadvantage (c) was the shape factor could only be quite poor. A common error of belief with r.f. filters of this type is that the filter receives one signal and one signal only.

Figure 1 - TRF three variable capacitors ganged to track together.

Let's consider this in some detail because it is critical to all receiver designs. When we discuss bandwidth we mostly speak in terms of the -3dB points i.e. where in voltage terms, the signal is reduced to .707 of the original.

If our signal sits in a channel in the a.m. radio band where the spacing is say 10 Khz e.g. 540 Khz, 550 Khz, 560 Khz.... etc and our signal, as transmitted, is plus / minus 4Khz then our 550 Khz channel signal extends from 546 Khz to 554 Khz. These figures are of course for illustrative purposes only. Clearly this signal falls well within the -3dB points of 10 Khz and suffers no attenuation (reduction in value). This is a bit like singling one tree out of among a lot of other trees in a pine tree plantation.

Sorry if this is going to be long but you MUST understand this basic principle.

Figure 2 - TRF shape factors against ideal

In an idealised receiver we would want our signal to have a shape factor of 1:1, i.e. at the adjacent channel spacings we would want an attenuation of say -30 dB where the signal is reduced to .0316 or 3.16% of the original. Consider a long rectangle placed vertically much like a page printed out on your printer. The r.f. filter of 10 Khz occupies the page width at the top of the page and the bottom of the page where the signal is only 3.16% of the original it is still the width of the page.

In the real world this never happens. A shape factor of 2:1 would be good for an L.C. filter. This means if the bottom of your page was 20 Khz wide then the middle half of the top of the page would be 10 Khz wide and this would be considered good!.

Back to T.R.F. Receivers - their shape factors were nothing like this. Instead of being shaped like a page they tended to look more like a flat sand hill. The reason for this is it is exceedingly difficult or near impossible to build LC Filters with impressive channel spacing and shape factors at frequencies as high as the broadcast band. And this was in the days when the short wave bands (much higher in frequencies) were almost unheard of. Certain embellishments such as the regenerative detector were developed but they were to some extent unsatisfactory.

In the 1930's Major Armstrong developed the superhetrodyne principle.

Reflex Theory

2010-09-16T20:00:00.000-07:00

Reflex Circuits: "A reflex amplifier is one which is used to amplify at two frequencies - usually intermediate and audio frequencies". - F. Langford-Smith, Radiotron Designers Handbook, Australia, 1953, P.1140

The reflex system consists of using an IF amplifier stage and after detection to return the audio portion to the same stage where it is then amplified again. Since in fig. 1. two signals of widely different frequencies are amplified, this does not constitute a "regenerative effect" - Oh gee whiz! and the input and output of these stages can have split audio/IF loads.

Figure 1 - reflex receiver block diagram

In fig. 2. the IF signal (e.g. 455 Khz) is fed through T2 to the detector circuit D1, C3 and VR1. The detected audio appears across the volume control VR1 and is returned through C4 to the cold side of the secondary of T1.

Since the secondary of transformer T1 consists of only a few turns of wire, it is essentially a short circuit at audio frequencies. C1 bypasses the IF signal otherwise appearing across the parallel combination of R1 and R2. The emitter resistor R3 is bypassed for both audio and IF by electrolytic capacitor C2.

Figure 2 - Reflex I.F. - Detector Circuit

After amplification, the audio signal appears across R4 from where it is then fed to the audio output stages. C5 bypasses R4 for IF frequencies and the primary of transformer T2 is essentially a short circuit for the audio signal.

The advantage of reflex circuits is that one stage produces gain otherwise requiring two stages with resulting savings in cost, space, and battery

drain.

The disadvantages of such circuits are that the design is considerably more difficult, although once a satisfactory receiver has been designed, no outstanding difficulties should be encountered.

Other significant difficulties are a somewhat higher amount of "playthrough" (i.e. signal output with volume control at zero setting), and a minimum volume effect. The latter is the occurrence of minimum volume at a volume control setting slightly higher than zero. At this point, the signal is distorted due to the balancing out of the fundamentals from the normal signal and the out-of-phase playthrough component.

BIBLIOGRAPHY

1. F. Langford-Smith, Radiotron Designers Handbook, Australia, 1953

2. G.E. Transistor Manual 1964, 1969

Superhet Theory AM & FM

2010-09-16T19:55:00.000-07:00

This is quite a lengthy document and contains schematics as .gif files. It may take some time to download - but worth the wait. Please be patient.

PRINT THIS TUTORIAL OUT NOW:

This tutorial will teach you in very easy steps how to design basic radio receivers. I will attempt to de-mystify most aspects of design by my usual extremely casual approach to an electronic tutorial. It doesn't matter whether you are a short wave listener, an A.M. radio dx'er, into hobby electronics or amateur radio design, the broad basic principles will still apply.
TYPES OF RADIO RECEIVER

Basic crystal set.
A T.R.F. Receiver.
A Superhetrodyne Receiver.
the Reflex Receiver.
1. The first receiver built by a hobbyist is usually the plain old crystal set. If you are unfamiliar with the design then check out the crystal set page.
2. The T.R.F. (tuned radio frequency) receiver was among the first designs available in the early days when means of amplification by valves became available.
The basic principle was that all r.f. stages simultaneously tuned to the received frequency before detection and subsequent amplification of the audio signal.
The principle disadvantages were (a) all r.f. stages had to track one another and this is quite difficult to achieve technically, also (b) because of design considerations, the received bandwidth increases with frequency. As an example - if the circuit design Q was 55 at 550 Khz the received bandwidth would be 550 / 55 or 10 Khz and that was largely satisfactory. However at the other end of the a.m. band 1650 Khz, the received bandwidth was still 1650 / 55 or 30 Khz. Finally a further disadvantage (c) was the shape factor could only be quite poor. A common error of belief with r.f. filters of this type is that the filter receives one signal and one signal only.
Let's consider this in some detail because it is critical to all receiver designs. When we discuss bandwidth we mostly speak in terms of the -3dB points i.e. where in voltage terms, the signal is reduced to .707 of the original.
If our signal sits in a channel in the a.m. radio band where the spacing is say 10 Khz e.g. 540 Khz, 550 Khz, 560 Khz.... etc and our signal, as transmitted, is plus / minus 4Khz then our 550 Khz channel signal extends from 546 Khz to 554 Khz. These figures are of course for illustrative purposes only. Clearly this signal falls well within the -3dB points of 10 Khz and suffers no attenuation (reduction in value). This is a bit like singling one tree out of among a lot of other trees in a pine tree plantation.
Sorry if this is going to be long but you MUST understand this basic principle.
In an idealised receiver we would want our signal to have a shape factor of 1:1, i.e. at the adjacent channel spacings we would want an attenuation of say -30 dB where the signal is reduced to .0316 or 3.16% of the original. Consider a long rectangle placed vertically much like a page printed out on your printer. The r.f. filter of 10 Khz occupies the page width at the top of the page and the bottom of the page where the signal is only 3.16% of the original it is still the width of the page.
In the real world this never happens. A shape factor of 2:1 would be good for an L.C. filter. This means if the bottom of your page was 20 Khz wide then the middle half of the top of the page would be 10 Khz wide and this would be considered good!.
Back to T.R.F. Receivers - their shape factors were nothing like this. Instead of being shaped like a page they tended to look more like a flat sand hill. The reason for this is it is exceedingly difficult or near impossible to build LC Filters with impressive channel spacing and shape factors at frequencies as high as the broadcast band. And this was in the days when the short wave bands (much higher in frequencies) were almost unheard of. Certain embellishments such as the regenerative detector were developed but they were mostly unsatisfactory.
In the 1930's Major Armstrong developed the superhetrodyne principle.
3. A superhetrodyne receiver works on the principle the receiver has a local oscillator called a variable frequency oscillator or V.F.O.
This is a bit like having a little transmitter located within the receiver. Now if we still have our T.R.F. stages but then mix the received signal with our v.f.o. we get two other signals. (V.F.O. + R.F) and (V.F.O. - R.F).
In a traditional a.m. radio where the received signal is in the range 540 Khz to 1650 Khz the v.f.o. signal is always a constant 455 Khz higher or 995 Khz to 2105 Khz.
Several advantages arise from this and we will use our earlier example of the signal of 540 Khz:
(a) The input signal stages tune to 540 Khz. The adjacent channels do not matter so much now because the only signal to discriminate against is called the i.f. image. At 540 Khz the v.f.o. is at 995 Khz giving the constant difference of 455 Khz which is called the I.F. frequency. However a received frequency of v.f.o. + i.f. will also result in an i.f. frequency, i.e. 995 Khz + 455 Khz or 1450 Khz, which is called the i.f. image.
Put another way, if a signal exists at 1450 Khz and mixed with the vfo of 995 Khz we still get an i.f. of 1450 - 995 = 455 Khz. Double signal reception. Any reasonable tuned circuit designed for 540 Khz should be able to reject signals at 1450 Khz. And that is now the sole purpose of the r.f. input stage.
(b) At all times we will finish up with an i.f. signal of 455 Khz. It is relatively easy to design stages to give constant amplification, reasonable bandwidth and reasonable shape factor at this one constant frequency. Radio design became somewhat simplified but of course not without its associated problems.
We will now consider these principles in depth by discussing a fairly typical a.m. transistor radio of the very cheap variety.
THE SUPERHETRODYNE TRANSISTOR RADIO
I have chosen to begin radio receiver design with the cheap am radio because:
(a) nearly everyone either has one or can buy one quite cheaply. Don't buy an A.M. / F.M. type because it will only confuse you in trying to identify parts. Similarly don't get one of the newer I.C. types.
Just a plain old type probably with at least 3 transformers. One "red" core and the others likely "yellow" and "black" or "white". Inside will be a battery
compartment, a little speaker, a circuit board with weird looking components, a round knob to control volume.
(b) most receivers will almost certainly for the most part follow the schematic diagram I have set out below (there are no limits to my talents - what a clever little possum I am).
(c) if I have included pictures you know I was able to borrow either a digital camera
or had access to a scanner.
Important NOTE: If you can obtain discarded "tranny's" (Australian for transistorised am radio receiver) by all means do so because they are a cheap source of valuable parts. So much so that to duplicate the receiver as a kit project for learning purposes costs about $A70 or $US45. Incredible. That is why colleges in Australia and elsewhere can not afford to present one as a kit.

Figure 1 - 1
Now that's about as simple as it gets. Alright get up off the floor. You will be amazed just how you will be able to understand all this fairly soon.
Unfortunately the diagram is quite congested because I had to fit it in a space 620 pixels wide. No I couldn't scale it down because all the lines you see are only one pixel wide.
So lets look at each section in turn, maybe re-arrange the schematic for clarity and discuss its operation. Now firstly the input, local oscillator, mixer and first i.f. amplifier. This is called an autodyne converter because the first transistor performs as a both the oscillator and mixer.

Figure 1 - 2

In Part 1 I finished by saying let's look at each section in turn, maybe re-arrange the schematic for clarity and discuss its operation. Now firstly the input, local oscillator, mixer and first i.f. amplifier. This is called an autodyne converter because the first transistor performs as a both the oscillator and mixer.
Figure 2 - 1
Now let's re-arrange the autodyne circuit into two circuits. The oscillator section and the mixer section.

Figure 2 - 2

Now obviously some components get duplicated across both sections not the least is our transistor.

OSCILLATOR SECTION

At power on, random noise produces a slight variation in the base current of Q1 which of course is amplified many, many times by the transistor producing a large variation in collector current. This a.c. signal from the collector induces a current in the secondary circuit which is tuned by our variable capacitor to the desired oscillator frequency. The coupling capacitor then couples the resonant frequency back into the emitter. With proper phasing (pri - sec winding turns in relation to one another) the feedback will be positive or regenerative and of sufficient voltage to keep the oscillator going.
The tuned secondary is an auto-transformer which matches the high tank impedance to the low impedance emitter.

MIXER SECTION

Here the .02 capacitor bypasses the base bias resistors to ground so the transistor as an oscillator is essentially a grounded base configuration.

What happens is the ferrite rod antenna picks up passing waves and tunes with the ganged tuning capacitor to the desired station whilst the other part of the ganged capacitor tunes the oscillator which is always a constant 455 Khz higher in frequency. Because of the transistor being biased in a non-linear region it also operates as a mixer. The IF load transformer is tuned to the difference frequency of 455 Khz and rejects all others.

Because the emitter is bypassed and the rf is injected into the base, the mixer is a grounded emitter configuration.

I.F. STAGES AND A.G.C.

There is nothing remarkable with the I.F. Amplifier stages. The gain of the first stage Q2 is controlled by an A.G.C. voltage (audio derived). The agc line is the purple (yuk!) line.

Figure 2 - 3

What happens is the signal passes through the if stages and is detected (rectified) by D2. Part of the rectified signal is applied across the volume control and transferred to later audio stages. Another part (purple) is applied back to the input of Q2 as opposing d.c., the strength of which varies in proportion to the received signal. On strong received signals the gain of Q2 is reduced while on weaker signals the gain becomes greater.

In theory, with such a mechanism the recovered audio signal going to our audio amplifier would be a constant level irrespective of the strength of our received signal on the loop antenna. This circuit has a number of limitations so D1 is used as an "extra agc circuit" in that on very high signals some of the signal gets shunted to ground.

On the whole the entire radio circuit has a great many limitations but please remember this is probably the cheapest receiver and definitely the most mass produced receiver produced in history. In 1976 they were available in lots of 10,000 (put your own brand label on) for eighty cents each. - I sold them.

On the other hand a fancier unit I purchased 14 years earlier (1962), cost me a full two weeks pay (about $800 today), it was a Sony and it still works fine to this day! - well ya just had to listen to the top 40 at the beach didnya? - wasn't I just the "wild one" back then. Oh where did it all go?.

Mainly f.m. receivers are of the superhetrodyne variety. Before we go into any depth about f.m. radio receivers let's consider the principal differences between a.m. and f.m. signals. At first glance it might seem I am merely stating the blinding obvious but the differences are indeed quite profound.

BACKGROUND TO FM RECEIVER DESIGN

An a.m. receiver relies upon the original carrier signal (station frequency) having been amplitude modulated. This means the original amplitude (strength) varies at an audio rate. Looking at figure 1 we can see an unmodulated carrier signal as it might be seen on an oscilloscope.

Fig 1. an unmodulated carrier signal

as you can see the amplitude of the carrier signal is unvarying, it remains constant in height looking from the top of the figure to the bottom of the figure. This carrier is common to both a.m. and f.m. signals.

Perhaps the a.m. carrier signal repeats each cycle from point (a) to point (b) - "blue" - in figure 2 below at the rate of 810,000 times a second, this represents a frequency of 810 Khz and would be in the a.m. radio band.

Figure 2. one complete cycle of signal

If the signal were varied at 101,700,000 cycles per second then it would be 101.7 Mhz and located in the f.m. radio band.

Now if the signal of figure 1 is amplitude modulated it looks like the signal in figure 3 below.

Figure 3. - an a.m. modulated signal

Here you will notice that the audio modulating signal which is depicted in red has varied the strength of the carrier signal which is depicted green for purposes of this illustration.

You will note my skills as a graphic artist leave much to be desired (hint: anyone able to contribute oscillograghs in .jpg or .gif formats?) but you should be able to see the carrier sine wave envelope is being varied in strength by the red audio signal. In the receiver circuit a diode detector can convert that envelope above back into the original audio signal for later amplification although some distortion does result.

It was to an extent this distortion property that people sought a better means of transmission. More important it was discovered that noise (either man made QRM or natural noise QRN) was amplitude in its properties.

I have depicted two blue lines in the diagram above, these represent noise impulses caused perhaps by automobile ignition, nearby fluorescent lighting, your computer or atmospheric noise such as a distant storm. Note the blue lines extend beyond the amplitude envelope, they could be many times the magnitude of the received signal.

Nearly everyone has experienced static crashes through an a.m. radio when nearby lightning strikes.

For these reasons frequency modulation evolved. Instead of varying the amplitude of the carrier signal, which remains constant, we vary the carrier frequency more or less by the audio frequency.

If a carrier signal is frequency modulated (fm) it looks like one below in figure 4

Fig 4 frequency modulated carrier

You should immediately note that the carrier frequency is varying yet the amplitude has remained constant.

REQUIREMENTS OF AN FM RECEIVER

This might be a good time to review the schematic circuit of an a.m. radio receiver.

Fig 5 a.m. bcb radio schematic

Unfortunately the diagram is quite congested because I had to fit it in a space 620 pixels wide.

Now the priciple differences between an f.m. radio versus an a.m. radio, and here for the moment we are talking about the entertainment variety, are:

(a) the need for VHF reception capability 88 - 108 MHz as against 0.54 - 1.65 Mhz for a.m. reception.

(b) the need for limiting action in the I.F. stages (see later discussion)

(c) a different means of detection of the audio i.e., recovering the frequency modulation.

(d) if we are talking f.m. stereo reception then some means of recovering left and right channel information.

In part 2 we will discuss these four basic requirements.

If you have got this far and this page proved helpful then please send me an email

Now the priciple differences between an f.m. radio versus an a.m. radio, and here for the moment we are talking about the entertainment variety, are:

(a) the need for VHF reception capability 88 - 108 MHz as against 0.54 - 1.65 Mhz for a.m. reception.

(b) the need for limiting action in the I.F. stages (see later discussion)

(c) a different means of detection of the audio i.e., recovering the frequency modulation.

(d) if we are talking f.m. stereo reception then some means of recovering left and right channel information.

V.H.F. RECEPTION

In most entertainment variety receivers i.e. 88 - 108 Mhz the local oscillator operates at a constant 10.7 Mhz higher or lower than the received signal e.g. 98.7 Mhz to 118.7 Mhz. If you need to know why then go to previous tutorial on a.m. receiver design and learn just why.

LIMITING ACTION

Limiting can be described as the action of overamplification where the signal is overdriven in stages and subsequently "clipped". Looking at figure 5(a) below we can imagine what happens when it is amplified and clipped (5b), amplified once again and clipped again (5c).

Figure 5. - an a.m. modulated signal being clipped

Naturally we don't put a normal a.m. signal through a limiter, this is usually only done with f.m. signals. I simply provided figure 5 above so you could get the general idea. You should notice that all the amplitude modulation information (including noise) is progressively being removed. BTW 5(b) and (c) were simply done graphically by taking (a) resizing the height by 150% and cutting off the excess height (top and bottom) and repeating that exercise for (c). This is exactly what happens in a limiter only to a much greater amplification!.

To give you some idea of the amplification required for proper limiting go back to the old vacuum tube days where a good a.m. - i.f. amplifier might contain three vacuum tubes.

In the same period a good f.m. receiver may have had twelve or more tubes in the i.f./limiter stage.

MEANS OF DETECTION

A number of f.m. detection schemes have evolved over the years. The principal discrete ones were:

(a) F.M. Discriminator (figure 6)

Figure 6. - an f.m. discriminator

This discriminator simply works on the principal that with no modulation applied to the carrier there is no ouput at the detector. Briefly T1 converts the f.m. signal to a.m. and when rectified the output is still zero because they would be equal but opposite in polarity, if modulation is applied then there is a shift in the phase of the input component with a corresponding difference in the signals out of the diodes. The difference between these outputs is the audio.

As an aside, this is somewhat similar to some Automatic Fine Tuning (A.F.T.) schemes in some a.m. receivers, notably early T.V. receivers. With no frequency variation there is no output, with frequency drift there will be an output difference (in either direction) which is amplified and applied to front end tuning diodes for correction.

(b) Ratio Detector

The schematic looks a little similar to figure 6 but has a third (tertiary) winding on the secondary of T1, diode D2 has its polarity reversed and the two divider resistors are replaced by capacitors. This scheme was quite popular in entertainment type receivers. You detect f.m. but NOT a.m. and it placed some relaxation on the severe limiting requirements.

(c) Crystal Discriminator

Once favoured by radio amateurs but superseded by later I.C. designs

(d) Phase Lock Loops

Among the relatively newer designs and PLL's overcome many of the drawbacks and costs associated with building and aligning LC discriminators.

REVIEW SO FAR AND STEREO RECEPTION

Of necessity I have only given you a general overview and background so far and, for very good reasons.

Over the last 20 years developments in the manufacture of dedicated and complete f.m. receivers on a chip have made an in depth review of earlier information presented totally redundent.

These developments include companion devices to handle stereo reception.

In part 3 I will discuss a number of suitable integrated circuits which hopefully are not only readily available but relatively cheap to buy and experiment with.

Source: http://my.integritynet.com.au/purdic/index.html#fm

MW_Regen_5T_2 Transformers with tuning circuit

2010-09-14T21:51:00.000-07:00

R3 controls the Regeneration

The audio amplifier can be replaced by IC audio amplifier.

Germanium transistors are used here.

Source: http://www.roetta.it/ik3hia/transistor/Transistors_diagrams/home_made_jaguaro_II.jpg

Zenith_Superhet_6T_2 IF Transformers

2010-09-14T21:36:00.000-07:00

Zenith mod. Royal 50 - USA 1961. After the Regency TR-1 pocket radio success in 50's half, all the radio industries in the world was looking toward this kind of business. in U.S. the Zenith company got a big sell result with the Royal 50 series, made since 50's end trought the first 60's years in the Illinois plant. The circuit was a superetherodyne with 6 PNP germanium transistors; the tuning capacitor C1 was still an air insulation type, the antenna was a flat ferrite bar working also like support fo the L1 coil. The plastic case was made in different colors and the power requirements was done by a pair of very cheaper 1,5 v AA (LR6) size batteries (that allow a discrete autonomy). The sound was warm like in all the Zenith radios. The dimensions are 11 x 7 x 3.5 cm and the weight is 277 g with the batteries.

Source: http://www.roetta.it/ik3hia/pages/transistors/zenith_royal_50.htm

MW_Reflex_2T_3 Transformers and Tuning Circuit

2010-09-14T20:50:00.000-07:00

It has been interesting analyzing these radios. You have to give the Japanese credit for even making a radio that can drive a speaker with only 2 transistors! Basically, the first transistor (Q1) performs double-duty. It first acts as an RF amplifier, with some of the signal being fed back to the antenna coil to provide some regeneration for better selectivity and sensitivity. (This also results in a non-linear amplification of the signal which results in noticeable distortion.)

The RF (radio frequency) signal is then rectified ("detected") by the diode, and then the resultant audio signal is fed back to the base of the first transistor where it acts as the first AF (audio frequency) amplifier. (This is called a "reflex" circuit.) The audio signal is then fed through an interstage transformer to Q2 (the second transistor). The transformer provides impedance matching.

The second transistor acts as a power amplifier, with the output signal going through an audio output transformer (to provide impedance matching again), and then finally to the speaker. Everything about this circuit is designed to provide maximimum gain; consequently there is no AGC (automatic gain control), and stronger stations come in a lot louder than weaker stations; unlike 6-transistor (or more) radio circuits which have an AGC circuit or function.

Source: http://www.transistor.org/FAQ/two-transistor.html

MW_Regen_3V

2010-09-14T19:46:00.000-07:00

Radio Star, a Selbstbauempfänegr with K - Tubes
of Bastelkarpo "Peter

Hi Jogi !
After I had so now 's already announced several times , I 'm now seriously. So here it is , my Audion receiver in the style of the '20s. (I hope I get any trouble now , because I have no attempt Audion permission. The kingdom telegraph company may forgive me !)

Completion had been delayed several times but still . Time I had no time , then missed the KL one , something was certainly running in between. Moreover, in parallel, I still puttering on other projects and then the thing properly taken time to complete. Now it is finally finished and I 'm actually quite pleased with my work .
My idea was to build a receiver , without being based on an industrial unit , built as it perhaps an ambitious radio hobbyists in the 20s , 30s. In addition I wanted to use from my vast collection of old components as possible , so that 's fairly original style acts .
From the beginning, the question arose as to the appropriate tubes. Unfortunately I could not draw on stocks , and so I researched only once for prices and offers. This turned out to fast, the tubes of the base criteria is Europe RE - had blown my budget range .
I had at that time even Mr. TSV supply store (see company links), because he was still living here in Bln . Zehlendorf , visited and bought some things from him. So I was including in the possession of the beautiful cardboard cover for the battery anode .
Mr. supply is an extremely nice and dedicated contemporary and I could entertain myself for hours with him, his own collection of historic instruments and his lovingly crafted replicas, just great.
In short, he had me put on the tubes of the K - series. These are apparently still present in larger quantities or are in the favor of collectors and hobbyists is not as high , at least they are more often to get in good or even mint condition.

I have my " auction in the bay , and the prices are still very fair. These tubes are created for such a historic radio like , look great and are powerful enough for this purpose . They are also very economical with the heating and can eat only a very practical Bleiaccuzelle . My 5- ampere hour Accu lasts forever , until it is loaded once and again. - I have since taken an American - Dryfit Acku of large C, built it into a chic box and that's it !

The anode battery, of which I had already mentioned the cardboard cover , I placed in a plywood enclosure. The sockets are not connected to the grid , because I will not build such a radio again probably . If I may yet need me, I can always upgrade a couple of voltage regulators.

I had been thinking only about the use of 9 volt batteries 6F22, but then I got this nice 12 volt Dryfitaccu given is enough space in the housing and thus I then tinkered a little transverter for 50 , 70 and 90 volts.
This seemed contrary to my profession as an auto electrician. We often fall in the company of defective ballasts for 24 volt 8 watt fluorescent lamps, so I played around a little bit tuned swing , still safe at 12 volts .
So the charred part of the circuit board sawed off , converter transformer on it three new secondary coils , made small circuit board with the three rectifiers and Siebketten , soldered in a copper sheet metal case , laying out capacitors voltages , and, behold, works fine. No interference spectrum to determine .
Among the 90 volt socket , I 've placed a miniature switch that switches the transverter when I plug a plug.

The receiver , I can either run through headphones or my Freischwingerlautsprecher . With headphones, but it is recommended that a reinzustecken KL upkeep and a KC 1, otherwise fly apart one 's ears ! This is easily possible , because even the center pin for the KC 's screen grid at a non-existent.

When building the Laustsprechers I 've long thought about how I make the case. Again, top round, as in my " Volxempfänger "- no thanks , of which I still had enough - too much work and work takes even known to work for you!
So I 've got it done so , as shown in the picture.

auszufiedeln The speaker grille and the two rings blend with the coping saw to me was enough . Some people have a tennis elbow , I have a Laubsägearm !
Inside an old potters DKE chair, has already seen the better times. The time was probably in a damp basement , was completely warped and swollen in the basket until I get back with a neat paint strength. For this purpose, he reaches even the sealed box and denied a look.

Only gewebeisoliertes cable and a few reasonable old German banana plugs for heating, anode and speaker cables I have to get me somewhere. I used the rubber lines just do not fit to do so. Weis someone a reference source? I like the Jan W. I do not really , but would be ever better.

On Audion even I had of course the most work. To the circuit there is really little to say , it is generally known and I have modified according to an old radio hobby book Einkreiserschaltungen for my purposes.

Switching to LW I have omitted, and the Rückkopplungsdrehko waived because I yes to feedback control the coils Schwenker use . The variable capacitor used in place of the capacitor I have calculated so that the adjustment of the pivot coil providing a safe use of feedback.
Schwenker the coils and the honeycomb coil , I myself have made , making the need for a job I certainly do not mention here. The details I have shown increases . The small label to the phone jacks come from the way Mr. supply , they round off the whole thing.

The rotary knob for the vote, I would still replace it with a larger, more beautiful model, when one comes to me sometimes in the fingers. Maybe someone knows so well for a source, a cast of a historical button I would be enough . In the bay are yes and then offered these old knobs, but the prices but then I have mostly put off .

The case I made as before in all my equipment from plywood, stained and painted with satin paint. The small types of labels I have yet elaborately etched on brass plate, for the speaker I have it printed on foil and glued on copper plate , see above the first photo.

The interior used parts I have, of course durchgemessen before use.

Batteries ran, ran headphones and the receiver played from the start. I then wrapped some comb coils with other windings (the copper wire is gewebeisolierte see Oppermann , above) and played around with it. Here in Berlin, so the local station expresses everything , and I 'm curious what makes the receiver on my land , away from the Berlin electro- bell , on a long wire antenna ...

So, I hope you enjoyed it,
many greetings from Peter roaring tube ( Bastelkarpo ).

Source: Main Page

MW_TRF_Audion_3V

2010-09-14T19:28:00.000-07:00

Battery-powered audio receiver ( 0- V -2) for medium

Since I had several Subminiaturröhren 1SH29B I have already used in my " KW- tube Audion with 12 V operating voltage , " Originated the idea of building in a small wooden box (" Asbach- Uralt " brandy praline mixture) an audio receiver for headphone operation . To keep the circuit on the RF side simply , there is only one sound stage , followed by NF- 2 levels.
The anode voltage of 27 V supply 3 pieces of 9 V battery ( 6LR61, 522, 6AM6 ) (alternatively battery possible, however, give the sum of only 25.2 V), the Heizpannung a 1.2V NiCd battery pack - with me - 2200 mAh capacity. After all, the heating current is 186 mA for the three tubes .
The feedback is controlled by changing the screen voltage to the pentode .
When a spooled ferrite inductor was of unknown origin (about 80 turns, then used for medium ). Of thin copper wire about 40 turns of feedback winding as were applied in addition (the old Auskoppelwicklung I have removed).

Click for a larger representation on the circuit diagram !

1SH29B
Some of the data from the Russian 1SH29B Datasheet:
Heizpannung : 1.2 or 2.4 V ( maximum 1.4 or 2.8 V , minimum 0.95 , or 1.9 V)
Heating current : 62 mA or 30
Anode voltage: 60 V (maximum 150 V )
Screen grid voltage: 45 V (maximum 120 V)
Anode current with grid voltage = 0 V : 5.3 mA
Screen grid current with grid voltage = 0 V : 2.5 mA
Slope : 2.5 mA / V ( at 0.95 V heating voltage at least 1.2 mA / V)
Maximum anode current: 8 mA
Maximum anode load: 1.2 W
When heating the center tap is brought out (pin 1 or better wire 1 ), at 1.2 V heating voltage is " + ", then connected to the two ends ( wire 4 and 6) on "-" ( cathode). You can operate the tube as in this case also at 2.4 V filament voltage on the wires 4 and 6, a wire ( center tap ) remains then unconnected.

A heating ( +), marked with colored dot , one is the center tap of the filament !
2 brake grid
3 screen grid
4, 6 heating ( -) and cathode
5 Shield
7 grid
The anode terminal is the wire at the other end of the Subminiaturröhre .

Notes / Experience
The volume potentiometer is not necessary for operation only on the ferrite .
More important would be a fine setting for the variable capacitor - is the little knob in my case directly mounted on the axle , the tuning a filigree .
If the feedback does not work , swap the connections of the feedback winding .
My device shows a marked microphonic .
With the ferrite antenna is especially in the evening / night satisfactory reception possible . The receive performance increases significantly if a (brief , a few meters ) is auxiliary antenna connected.

Last updated 11/02/2003

( c ) L. Höll 2003
Source: Homepage of DK3WI

Valve radio shaped like old telephone

2010-09-14T18:25:00.001-07:00

Guild 556 "Country Belle" Telephone Radio (1956)

1950's, 5-tube radio. Radio resembles an early 1900s wall telephone. Radio on/off switch is the receiver. Tuner is the crank, and knobs are for the tone and volume.

MW_Reflex_2T

2010-09-13T20:30:00.001-07:00

MW_Reflex_2T

2010-09-13T20:28:00.001-07:00

MW_Reflex_2T

2010-09-13T20:20:00.001-07:00

MW_Reflex_2V_Transformerless

2010-09-13T20:18:00.001-07:00

MW_Reflex_1V

2010-09-13T20:15:00.001-07:00

MW_Reflex_1T

2010-09-13T20:13:00.001-07:00

MW_SW_1V_Variometer Tuned

2010-09-13T20:10:00.001-07:00

MW_TRF_1V_2T

2010-09-13T20:07:00.001-07:00

Transistor Stabalization

2010-09-13T20:04:00.000-07:00

Reflex_3V

2010-09-13T19:58:00.000-07:00

80m_Direct Conversion_2T_1IC

2010-09-08T18:17:00.000-07:00

Source: http://home.alphalink.com.au/~parkerp/projects/dcrx.gif

40m_Direct Conversion_3T_1IC

2010-09-08T17:59:00.000-07:00

40 meter Direct Conversion Receiver

Using the circuit of 40-metre band direct-conversion receiver described here, one can listen to amateur radio QSO signals in CW as well as in SSB mode in the 40-metre band. The circuit makes use of three n-channel FETs (BFW10). The first FET (T1) performs the function of ant./RF amplifier-cum-product detector, while the second and third FETs (T2 and T3) together form a VFO (variable frequency oscillator) whose output is injected into the gate of first FET (T1) through 10pF capacitor C16. The VFO is tuned to a frequency which differs from the incoming CW signal frequency by about 1 kHz to produce a beat frequency in the audio range at the output of transformer X1, which is an audio driver transformer of the type used in transistor radios. The audio output from transformer X1 is connected to the input of audio amplifier built around IC1 (TBA820M) via volume control VR1. An audio output from the AF amplifier is connected to an 8-ohm, 1-watt speaker. The receiver can be powered by a 12-volt power-supply, capable of sourcing around 250mA current. Audio-output stage can be substituted with a readymade L-plate audio output circuit used in transistor amplifiers, if desired. The necessary data regarding the coils used in the circuit is given in the circuit diagram itself.

Source :www.electronic-circuits-diagrams.com

http://www.electronic-circuits-diagrams.com/radio_circuits.shtml

SW_Direct Conversion_3IC

2010-09-08T17:47:00.000-07:00

Direct Conversion Receiver.

Description.

Direct Conversion receivers are the most popular QRP receivers for the reception of SSB or CW modes. The availability of IC's, improves their performance, and reduces parts count, making them simple to build, and easy to use. With a product detector, the input signal is mixed with a VFO signal close to the input signal, the result is an audible beat tone, which is processed. In this popular, and widely adopted DCRX an NE/SA602 is used as the product detector. The resulting audio is filtered, and then amplified to a comfortable level for headphone use. In this design from W1FB, Q1, which could be a MPF102 or 2N4416, is the VBFO, Q2 provides audio pre-amp, IC2 audio band pass filtering with a center of 700Hz, IC3 gives audio gain for headphones. Jumper J1 should be removed to provide muting for transmit periods. This can be done using a relay or external PNP switch. The receiver can run from a 9V, or 12V DC source. This design can be improved by adding a RF gain control, substituting the SA/NE602 with a SA/NE612, improving the audio amplification, and filtering, adding a digital frequency readout, a RF filter with sharper roll-out, and using varicap tuning rather than air-variable tuning(C16 is an air-variable, while C18, and C3 can be trimmers. C3 should be an air-variable at 80M) This particular design has a low parts count, and can be reproduced on a breadboard, or perf-board. Note that the audio isolation transformer may be hard to find, but can be substituted with an audio interstage transformer with a 10K Primary, and 2K Secondary. Far Circuits makes a PCB(Universal Direct Conversion Receiver) board for this design.

Modified implemenation of above Direct Conversion RX.

Below is the schematic and Eagle(CADSOFT) board(2.25" x 1.95") file of a modified implementation of the above DCRX!

5Z4FT DCRX Board File

Source: http://www.qsl.net/5z4ft/dcrx.html

MW_Direct Conversion Reciever_2T_3GeD

2010-09-06T10:47:00.000-07:00

Two versions of the same thing. It shows the simple and powerful theory of Zero-IF Receiver.

Read the note in red ... it clarifies the secret behind this beautiful design. This design is simple 2 transistors one. 3 Ge Diodes are used. The two designs differ mainly by the coil. Anyway, the high impedance earphone can be overcomed by OP-AMP amplifier. The main purpose of this article is to clarify the Zero-IF theory = Direct Conversion = Homodyne :)

Special thanks to Mike for his effort and kind posting of his work.

The Iraqi Bourgois!

----------

My Homodyne Receiver by Mike Tuggle

The Art Photo

Description. My 2007 1-AD Contest set was the “Modern Homodyne,”
designed and described by G.W. Short in a highly recommended article:

http://www.vintageradio.me.uk/radconnav/transtrf/

I made several modifications to, and omissions from,
Short's original circuit:

1. ferrite rod coil L1 replaced by basketwound 660/46 litz coil

2. no gimmick capacitor across gate resistor R1
-- not necessary at BCB frequencies

3. no shunt detector diode D3 in the half-wave doubler
– simple, single diode detector D4 only

4. no low-pass audio filter -- it eliminates highs,
but it is a real detriment to DX listening

5. no final audio amp stage -- not necessary
when using sound powered phones

6. no ground plane under circuit board or other shielding
(actually, I forgot these, and the circuit seems
to work just fine without them).

Performance.

Antenna. The Homodyne uses no outside antenna. Its tuning coil
serves as the antenna -- in this case it's the 6" diameter
(that's right, 6 INCH) litz basketwound coil L1, mounted as
a rotatable, tuned loop on top of the set. This coil is all
the antenna there is. I'm reasonably sure of no coupling
going on to my disconnected outside antenna. The lead-in is
several feet away; the set works well in other rooms far
away; and the loop exhibits nice directionality. But, larger
coils tried, including a 1-meter diameter loop antenna,
tended to overload the set and ruin its selectivity.

Selectivity. Feedback works like none I've ever experienced.
There is no popping in and out of regeneration. As feedback
is increased, the squeal-free tuning range about the desired
station narrows, and the volume increases. Further increasing
feedback, the squeal-free region closes out, and tuning the
station is very touchy -- just like a BFO’ed exalted-carrier
set which is always in oscillation. In essence, feedback
control R7 can vary the selectivity from broad as a barn
to razor sharp, depending upon one’s need..

Noise. One drawback to the Homodyne is it is very sensitive
to line noise – perhaps because it is so sensitive to
everything else as well. During evening listening sessions
I can hear the ambient line noise level steadily increase
as neighbors switch on SCR light dimmers, cable TV’s,
fluorescents, etc. This din usually increases to a point
when some idiot switches on something defective, and the
noise becomes as loud as an SCR operating in my own house.
Unfortunately, the power conduit to the house is right
outside the radio room wall. Switching off the main power
provides little relief. By then, the noise has been induced
into the phone lines, and the cat’s out of the bag. I get a
good measure of relief by retreating with the set to an
outpost on the electrically quiet lanai (enclosed sun porch)
in back. Having only a 6-inch loop antenna makes this feasible.

Wave-Trapping. The directional pattern of the rotatable loop
antenna reduces the need for wave traps for all but the strongest
interfering signals. I got by in the contest fairly nicely
without using any wave traps. Since the loop antenna pattern
has sharp nulls off the faces and broad peaks off the ends,
directing the antenna to exactly null an interfering station
usually leaves enough gain for the weak DX station, whatever
direction it may lie in. One really weird effect I haven’t had
time to investigate is, on strong local stations and in-house
line noise, the loop antenna shows a sharp null off only one
face but not the other. This means the loop is showing a
cardiod (heart-shaped) pattern instead of the usual figure-eight.
One of the real beauties of a loop antenna is that, unlike
other traps, it lets you ‘trap’ interfering signals on the
same frequency as the desired DX signal.

Without a doubt, the Homodyne is the finest broadcast band
DX set I’ve ever operated -- bar none. That includes the likes
of the Hammarlund HQ-180A, Collins 51S-1, and others.

How It Works. Drawing extensively from G.W. Short’s
article, here is how the set works:
Amplifier. The set is basically a two-stage RF
amplifier using a “direct-coupled, complementary-cascade”
transistor pair TR1-TR2. All tuning is done by L1-C2,
the 6-inch basket coil-variable capacitor tank. Little
amplification is done by the 2N3819 JFET TR1 – it serves
mainly to match the high impedance input from the tuning
tank, preserving the tank’s high Q. Most of the actual
gain comes from the PNP germanium
AF 239 UHF-type transistor TR2.

Oscillator. Positive feedback* derived at the collector of the
AF 239 (‘collector follower’) is applied to the 2N3819 gate
(input) to generate strong oscillation at approximately the
same frequency as the incoming carrier**. The 10 k-ohm
pot R7 controls feedback level.

(* In going from 2N3819 gate to AF 239 collector, the phase
is inverted twice, for a 360 degree ‘total phase shift,’ thus
leaving the feedback in-phase with the input. At least,
that’s true at the lower frequencies including the broadcast
band. At short waves, phase shift creeps in
and must be compensated for.)

Locking. An important feature of this local oscillation is
that it will lock onto the frequency of the incoming signal’s
carrier, even if the tank is not tuned exactly to that carrier.
Ideally when the oscillator tank is tuned to the ‘vicinity’
of a weak signal, it will lock on that signal and not on much
stronger signals that may lie in adjacent channels.

Limiter. The front-to-back diode pair D1-D2 serves as a limiter
that suppresses the modulation of the fed-back carrier and
prevents the level of oscillation from becoming too large.
Ideally the feedback consists of un-modulated carrier of fixed
amplitude. The 10 k-ohm fixed resistor R6 feeding the limiter
allows good clipping and at the same time prevents the limiter
from loading down the detector input.

Demodulator / Mixer / Detector. Demodulation (detection) occurs
at diode D4 that goes to the output. Incoming signal
(carrier-plus-sidebands = RF input) is mixed with the
locally-generated oscillation (LO) at the carrier’s frequency.
The difference frequency product of the two mixed signals
emerges as the so-called ‘intermediate frequency’ (IF) which
in our case is simply the audio frequency. Any mixing products
of the LO with adjacent channel signals are much higher in
frequency and thus out of the audible range. This is how
‘direct conversion’ receivers of this type
get their excellent selectivity.

Acknowledgments: Special thanks to Macrohenry for originally
recommending the Homodyne circuit to me, and to Brian Hawes for
tracking down the special AF 239 transistor
as well as the 2N3819 FET for me.

-------------
The original sources ofinformation are for those sites: My comments are in red and blue

Source: http://www.crystalradio.us/1adradios/1ad-2007-2.htm#tuggle
**Note: This is why it is called Zero-IF (Direct-Conversion Receiver).

Theory_Direct Conversion Receiver

2010-09-06T10:45:00.000-07:00

Direct-conversion receiver

From Wikipedia, the free encyclopedia

Jump to: navigation, search

In telecommunication, a direct-conversion receiver (DCR), also known as homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design that demodulates the incoming signal by mixing it with a local oscillator signal synchronized in frequency to the carrier of the wanted signal. The wanted modulation signal is obtained immediately by low-pass filtering the mixer output, without requiring further detection. Thus a direct-conversion receiver requires only a single stage of detection and filtering, as opposed to the more common superheterodyne receiver design, which converts the carrier frequency to an intermediate frequency first before extracting the modulation, and thus requires two stages of detection and filtering.

[hide]

[edit] Properties

Unwanted signals are left on carriers of the frequency difference between their original carrier and that of the wanted signal. There is no detection of the unwanted signals since the whole signal path is kept free of non-linearity. Unwanted signals can be completely rejected by use of a low-pass filter on the audio output. The receiver consequently has the advantage of high selectivity, and is inherently a precision demodulator. The principles can be extended to permit separation of signals whose sidebands overlap, and they also lead to improved detection of pulse-modulated signals.

[edit] History and applications

The homodyne was developed in 1932 by a team of British scientists searching for a method to surpass the superheterodyne. This new type of receiver was later renamed the synchrodyne, and not only proved to have superior performance, but the single conversion stage also had lower complexity and power consumption. But the circuit after a period of time became unstable due to slight drift in frequency of the local oscillator. To counteract this drift, the frequency of the local oscillator was compared with the input by a phase detector so that a correction voltage would be generated and fed back to the local oscillator, thus keeping it on lock. This type of feedback circuit evolved into what is now known as a phase-locked loop. While the method has existed for several decades, it had been difficult to implement due largely to component tolerances, which must be very tight for this type of circuit to operate well.

The circuit was not without other problems. Reverse-transmission paths can occur in the receiver. Local-oscillator energy can leak through the mixer to the antenna input and then re-enter the mixer. The overall effect is that the local oscillator energy would self-mix and create a DC offset. The offset could be large enough to swamp the baseband amplifiers and destroy signal reception. There were several work arounds to deal with this issue but these too added to the complexity of the receiver. Ultimately the higher costs were found to outweigh the benefits.

The modern usage of direct conversion technique started with publication of 'Direct Conversion - A Neglected Technique QST, Nov, 1968' in 1968 November's QST by Wes Hayward and Dick Bingham.

The widespread use of this principle did not begin until the development of the integrated circuit and incorporation of complete phase-locked loop devices in low-cost IC packages. These are no longer limited to the reception of AM radio, now being able to process more complex modulation schemes. Since then, direct-conversion receivers have been incorporated into many receiver applications, including cellphones, televisions, avionics, medical imaging apparatus and Software-defined radio systems.

[edit] See also

[edit] External links

Wikimedia Commons has media related to: Radio electronic diagrams

The History of the Homodyne and Syncrodyne The Journal of the British Institution of Radio Engineers, April 1954

Heterodyne

From Wikipedia, the free encyclopedia

Jump to: navigation, search

This article is about waveform manipulation. For the use of the term in poetry, see Heterodyne (poetry). For the webcomic characters, see Girl Genius.

In radio and signal processing, heterodyning is the generation of new frequencies by mixing (multiplying), two oscillating waveforms. It is useful for placing information of interest into a useful frequency range following modulation or prior to demodulation. The two frequencies are mixed in a vacuum tube, transistor, diode, or other signal processing device. Mixing two frequencies creates two new frequencies, according to the properties of the sine function; one is the sum of the two frequencies mixed, the other is their difference. These new frequencies are called heterodynes. Typically only one of the new frequencies is desired—the higher one after modulation and the lower one after demodulation. The other signal is filtered out of the output of the mixer.

[hide]

[edit] Origin and use of term

The word heterodyne is derived from the Greek roots hetero- "different", and dyn- "power" (cf. dynamis). The original heterodyne technique was pioneered by Canadian inventor-engineer Reginald Fessenden in 1901, but was not pursued very far because local oscillators were not very stable at the time.^[1] Heterodyning was invented by Fessenden as a technique to make the Morse code radiotelegraph (CW) signals used during the wireless telegraphy era audible.^[2] A "heterodyne" receiver had an oscillator circuit, called a local oscillator, that produced a radio signal that was adjusted to be close in frequency to the signal being received, so that when the two signals were mixed the difference or "beat" frequency was in the audible range. This produced a musical tone in the speaker, so the "dots" and "dashes" of Morse code were audible as beeping sounds. This technique is still used in radio telegraphy; the oscillator is now called a beat frequency oscillator.

Later, the superheterodyne receiver (superhet) was invented by Edwin Howard Armstrong in 1918, converting the incoming Radio Frequency (RF) to a fixed Intermediate Frequency (IF), using the heterodyne technique. The difference between the superhet and the original heterodyne is the use of a "sloppy" but tunable RF filter on the front end, a mixer circuit, a stable local oscillator (LO) and a fixed frequency high-gain band-pass amplifier.^[3] The original heterodyne technique tried to accomplish all of this in one stage thus producing an unstable amplifier.

[edit] How it works

In a superheterodyne receiver, the incoming radio signal of interest at frequency f_IN is mixed (that is, multiplied) with a second signal f_LO produced by an oscillator circuit in the receiver, called the local oscillator (LO). This mixing produces two new frequencies, at the sum (f_IN + f_LO) and difference (f_IN - f_LO) of the original frequencies. One of these two new frequencies is discarded, usually the higher one (f_IN + f_LO), by filtering it out of the mixer output. The remaining difference frequency is called the intermediate frequency (IF), and it is passed to a high gain amplifier, and signal processing that eventually extracts the desired modulation carried by the signal. Common choices for the IF frequency are 455 kHz in some AM radios and 10.7 MHz in FM radios. This process of shifting the RF signal down to a lower IF frequency is called "down conversion".

[edit] Mathematical principle

Heterodyning is based on the trigonometric identity:

The product on the left hand side represents the multiplication ("mixing") of a sine wave with another sine wave. The right hand side shows that the resulting signal is the difference of two sinusoidal terms, one at the sum of the two original frequencies, and one at the difference, which can be considered to be separate signals.

Using this trigonometric identity, the result of multiplying two sine wave signals, and can be calculated:

The result is the sum of two sinusoidal signals, one at the sum f₁ + f₂ and one at the difference f₁ - f₂ of the original frequencies

[edit] Mixer

The two signals are multiplied in a device called a mixer. In order to multiply the signals, the mixer must be a nonlinear component, that is, its output current or voltage must be a nonlinear function of its input. Most circuit elements in communications circuits are designed to be linear. This means they obey the superposition principle; if F(v) is the output of a linear element with an input of v:

So if two sine wave signals are applied to a linear device, the output is simply the sum of the outputs when the two signals are applied separately, with no product terms. So the function F must be nonlinear. Examples of nonlinear components that are used as mixers are vacuum tubes and transistors biased near cutoff (class C), and diodes. For lower frequencies, IC analog multipliers can be used which multiply signals precisely. Ferromagnetic core inductors driven into saturation can also be used. In nonlinear optics, crystals that have nonlinear characteristics are used to mix laser light beams to create heterodynes at optical frequencies.

[edit] Output of a mixer

To demonstrate mathematically how a nonlinear component can multiply signals and generate heterodyne frequencies, the nonlinear function F can be expanded in a power series (MacLaurin series):

To simplify the math, the higher order terms above α₂ will be indicated by an ellipsis (". . .") and only the first terms will be shown. Applying the two sine waves at frequencies ω₁ = 2πf₁ and ω₂ = 2πf₂ to this device:

It can be seen that the second term above contains a product of the two sine waves. Simplifying with trigonometric identities:

So the output contains sinusoidal terms with frequencies at the sum ω₁ + ω₂ and difference ω₁ - ω₂ of the two original frequencies. It also contains terms at the original frequencies and at multiples of the original frequencies 2ω₁, 2ω₂, 3ω₁, 3ω₂, etc.; the latter are called harmonics. These unwanted frequencies, along with the unwanted heterodyne frequency, must be filtered out of the mixer output to leave the desired heterodyne.

[edit] Applications

Heterodyning is used very widely in communications engineering to generate new frequencies and move information from one frequency channel to another. Besides its use in the superheterodyne circuit which is found in almost all radio and television receivers, it is used in radio transmitters, modems, satellite communications and set-top boxes, radar, telemetry systems, cell phones, cable television converter boxes and headends, microwave relays, metal detectors, atomic clocks, and military electronic countermeasures (jamming) systems.

[edit] Up and down converters

In digital communications signals can be transmitted in baseband or passband. On receiver side usually a downconverter is used to transform the signal from the passband back to the baseband for further processing. The local oscillator frequency is , with $f c$ being the carrier frequency. This results in a scaling of the received signal by and a phase shifting by $f c$ to the left, so that the resulting signal is located in the baseband.

A radio frequency upconverter is a device that takes an input of radio frequency energy of a specific frequency range and outputs it on a higher frequency. Likewise, downconverters take an input frequency and reduce it to a lower output frequency. Both converters are commonly used in transverters and satellite communications. Upconverters achieve this frequency conversion via heterodyning, the same principle as modern receivers and transmitters to offset the frequency.

[edit] Analog videotape recording

Many analog videotape systems rely on a downconverted color subcarrier in order to record color information in their limited bandwidth. These systems are referred to as "heterodyne systems" or "color-under systems". For instance, for NTSC video systems, the VHS (and S-VHS) recording system converts the color subcarrier from the NTSC standard 3.58 MHz to ~629 kHz.^[4] PAL VHS color subcarrier is similarly downconverted (but from 4.43 MHz). The now-obsolete 3/4" U-matic systems use a heterodyned ~688 kHz subcarrier for NTSC recordings (as does Sony's Betamax, which is at its basis a 1/2" consumer version of U-matic), while PAL U-matic decks came in two mutually incompatible varieties, with different subcarrier frequencies, known as Hi-Band and Low-Band. Other videotape formats with heterodyne color systems include Video-8 and Hi8.^[5]

The heterodyne system in these cases is used to convert quadrature phase-encoded and amplitude modulated sine waves from the broadcast frequencies to frequencies recordable in less than 1 MHz bandwidth. On playback, the recorded color information is heterodyned back to the standard subcarrier frequencies for display on televisions and for interchange with other standard video equipment.

Some U-matic (3/4") decks feature 7-pin mini-DIN connectors to allow dubbing of tapes without a heterodyne up-conversion and down-conversion, as do some industrial VHS, S-VHS, and Hi8 recorders.

[edit] Music synthesis

The theremin, an electronic musical instrument, uses the heterodyne principle to produce a variable audio frequency in response to the movement of the musician's hands in the vicinity of some antennas. The output of a fixed radio frequency oscillator is mixed with that of an oscillator whose frequency is affected by the variable capacitance between the antenna and the thereminist as that person moves her or his hand near the pitch control antenna. The difference between the two oscillator frequencies produces a tone in the audio range.

The Ring modulator is a type of heterodyne incorporated into some synthesizers or used as a stand-alone audio effect.

[edit] Optical heterodyning

A current active area of research is extension of the heterodyning technique to higher frequencies, particularly to light frequencies, which are above radio frequencies in the electromagnetic spectrum. This technique could greatly improve optical modulators, increasing the density of information carried by optical fibers. It is also being applied in the creation of more accurate atomic clocks based on directly measuring the frequency of a laser beam^[6].

Since optical frequencies are far beyond any feasible electronic circuit all photon detectors are inherently energy detectors not oscillating electric field detectors. However since energy detection is inherently "square-law" detection, it intrinsically mixes any optical frequencies present on the detector. Thus sensitive detection of specific optical frequencies is possible by optical heterodyne detection when two different (close-by) wavelengths of light illuminate the detector so that the oscillating electrical output corresponds to their difference frequency. This allows extremely narrow band detection (much narrower band than any possible color filter can achieve) as well as precision measurements of phase and frequency of a signal light relative to a reference light source, as in Laser Doppler Vibrometry.

This phase sensitive detection has been applied for Doppler measurements of wind speed, and imaging through dense media. The high sensitivity against background light is especially useful for LIDAR.

[edit] See also

[edit] References

[edit] Notations

Glinsky, Albert. Theremin: Ether Music and Espionage. Urbana: University of Illinois Press, 2000. ISBN 0-252-02582-2.
Nahin, Paul J. The Science of Radio. New York: Springer-Verlag, AIP Press, 2001. ISBN 0-387-95150-4.

[edit] Footnotes

^ Nahin, Paul. The Science of Radio. Page 91. Figure 7.10. Chapter 7. ISBN 0-387-95150-4.
^ Ashley, Charles Grinnell; Charles Brian Heyward (1912). Wireless Telegraphy and Wireless Telephony. Chicago: American School of Correspondence. pp. 15–16. http://books.google.com/books?id=pK-EAAAAIAAJ&pg=RA1-PA15.
^ Nahin, Paul. The Science of Radio. Page 285. Chapter 21. ISBN 0-387-95150-4.
^ Videotape formats using ¹⁄₂-inch-wide (13 mm) tape ; Retrieved 2007-01-01
^ Poynton, Charles. Digital Video and HDTV: Algorithms and Interfaces San Francisco: Morgan Kaufmann Publishers, 2003 PP 582, 583 ISBN 1-55860-792-7
^ http://tsapps.nist.gov/ts_sbir/abstracts/08abst1.htm see NIST subtopic 9.07.9-4.R for a description of research on one system to do this.

Retrieved from "http://en.wikipedia.org/wiki/Heterodyne"

Homodyne detection

From Wikipedia, the free encyclopedia

Jump to: navigation, search

Optical Homodyne Detection.

Homodyne detection is a method of detecting frequency-modulated radiation by non-linear mixing with radiation of a reference frequency, the same principle as for heterodyne detection.

In optical interferometry, homodyne signifies that the reference radiation (i.e. the local oscillator) is derived from the same source as the signal before the modulating process. For example, in a laser scattering measurement, the laser beam is split into two parts. One is the local oscillator and the other is sent to the system to be probed. The scattered light is then mixed with the local oscillator on the detector. This arrangement has the advantage of being insensitive to fluctuations in the frequency of the laser. Usually the scattered beam will be weak, in which case the (nearly) steady component of the detector output is a good measure of the instantaneous local oscillator intensity and therefore can be used to compensate for any fluctuations in the intensity of the laser.

[hide]

[edit] Radio Technology

In radio technology, the distinction is not the source of the local oscillator, but the frequency used. In heterodyne detection, the local oscillator is frequency-shifted, while in homodyne detection it has the same frequency as the radiation to be detected. See direct conversion receiver.

[edit] See also

[edit]

Source: Wikipedia

Reflex_1T_Basic Theory by Sir Douglas

2010-09-06T10:33:00.000-07:00

Source: http://www.retinascope.co.uk/reflextransistor.html

Antenna_CB Radio_105 inch 4 wires

2010-09-06T09:42:00.000-07:00

HOME MADE CB RADIO ANTENNA
HOW TO MAKE A CHEAP CB RADIO BASE STATION ANTENNA

How to make a Cheap and Easy Home Made CB Radio Antenna. This homemade cb radio antenna can be used for base station or portable operation. Just hang it and talk. This antenna is a "Quarter Wave Dipole" with Ground Radials. You may find this homemade cb antenna performs rather well if you do not have access to a typical base station antenna.

Step One: Get some 50 ohm coaxial cable to run from the cb radio to the wire antenna.

Step Two: Connect the center lead of coaxial cable to 105 inch piece of wire as seen in diagram above. Make sure the braided outer shield is not touching the center wire.

Step 3: Connect braided shield of coaxial cable to 1,2,3, or 4 pieces of 105 inch wire. These are the 4 wires pointing downward in the diagram above.

Tape the wires and cable so the wire that points straight up does NOT make contact with the four wires on the bottom. The 4 wires pointing down are all connected to each other and the shield braided outer part of the coaxial cable. The wire you use for the vertical antenna section and the ground plane wires is not important. Plastic coated speaker wire or salvaged extension cords wire will work fine.

Mounting tip: Put a plastic clothes hanger at the top of the wire antenna. Now scotch tape the hanger to a long wooden pole. Use pole to reach a tree branch and hang antenna in tree. As the plastic clothes hanger hangs on tree, scotch tape will come off to release pole. Let the 4 ground radial wires dangle.

Warning: Never install antenna near power lines. Always calculate distance of feed line so it snaps 20 feet before the antenna could make contact with a power line, should the antenna and coaxial cable become air born. i.e. the coaxial cable and antenna length combined should be at least 20 feet shorter than the nearest power line. More people die installing antennas every year than most people realize. In the 80's over 50 people a year gave their lives to put up antennas. Most of them were dead before the antenna even touched the wire. You don't have to touch it, you just have to be close enough to arc.

Source: http://www.livecbradio.com/home-made-cb-radio-antenna.htm

CB Radio_3T_Super-regen

2010-09-04T23:18:00.000-07:00

Sophisticated Low Tech: Three-Transistor Toy Walkie-Talkie
Although vacuum-tube “toy” walkie-talkies had appeared as hobby projects in the years following the second World War, they were too expensive for anyone to consider manufacturing them in volume as actual toys for children. The development of the transistor made such a toy a practical possibility. Jerry Norris, an engineer at Texas Instruments, was the first to act on this insight, and in so doing developed in 1962 the ancestor of all toy walkie-talkies [22]. This widely copied and ingenious circuit uses a single-transistor superregenerative amplifier/detector (yet another Armstrong invention), followed by two stages of audio amplification in receive mode (see Figure 16). When transmitting, the superregenerative stage becomes a stable crystal-controlled 27MHz oscillator, amplitude-modulated by an audio amplifier built out of the other two transistors. The speaker doubles as a microphone in this mode.

Transistor Q1 does all the RF work in this circuit. In receive mode, Q1 is configured as a Colpitts oscillator with unstable bias. An incoming RF signal establishes an initial condition from which oscillations build up exponentially, providing remarkable sensitivity. The bias is arranged to cut off (“quench”) the oscillations periodically at a rate high enough to sample the modulation at a super-Nyquist rate (this periodically quenched oscillation distinguishes superregeneration from regeneration). Thanks to ever-present nonlinearities, the transistor also amplifies the modulated RF signal asymmetrically. Hence, the collector current contains a component roughly proportional to the modulation itself. A low-pass filter consisting of C₉, L₄ and C₁₀ removes the RF component, passing only the modulation to the two-transistor audio amplifier made of Q2 and Q3.Figure 16: Jerry Norris’ superregenerative CB walkie-talkie [22]

While Q1 acts as a self-quenched LC oscillator in the receive mode, a quartz crystal is used to control the frequency of oscillation during transmit. Resistor R₆ is shorted out during transmit to prevent quenching.

The oscillator amplitude is roughly proportional to the collector supply voltage, so varying the supply voltage with an audio signal from Q2/Q3 amplitude-modulates the carrier. Although the distortion from this process hardly meets the standards of high fidelity audio, it is certainly adequate for voice communications, and most definitely adequate for a toy.

Because this simple circuit provides such large gain with so few transistors, it continues to dominate the toy walkie-talkie market, having been copied and modified countless times by manufacturers. The influence of Norris’ circuit it evident from having traced over twenty superregenerative walkie-talkie circuits over the years. In all of them, just one transistor does all of the RF work, with the remaining two (sometimes three) transistors serving as audio amplifiers. As with the All-American Five, variations among different manufacturers are relatively minor.

Source:

http://www.ieee.org/portal/site/sscs/menuitem.f07ee9e3b2a01d06bb9305765bac26c8/index.jsp?&pName=sscs_level1_article&TheCat=2171&path=sscs/07Fall&file=Lee.xml

Jerry Norris, “Three-Transistor CB Transceiver,” Electronics World, Nov. 1962, pp. 38-39.

Crystal Radio_SW

2010-09-01T21:49:00.000-07:00

Experimental Short-wave "Mystery"

Crystal Radio

by Ken Harthun

Copyright January 2001

This is not the typical crystal set construction article to which you may be accustomed; rather, it is a description of a few workable circuits that leaves plenty of room for experimentation if you are so inclined. You can build a fine working short-wave crystal set based on what I give you here. These circuits perform very well. However, I’m still experimenting with them and I challenge you to do the same, to discover what works best for you. Tinkering with a circuit, trying different things to see what works – and what doesn’t – is the essence of our hobby and is what keeps this particular rock head interested!

Because this set is experimental, I make no claims that this design – or any particular hookup that results from this article - is the ne plus ultra in short-wave crystal radios. We all know that the perfect crystal set does not exist. The "perfect" crystal set for my location is something that may or may not work for you (I have to deal with a 50Kw blowtorch that is located virtually in my backyard – you may be more fortunate).

My antenna is about 150 feet of wire in an inverted V with the apex at about 35 feet. Some of it runs every-which-way across my roof and into my radio room. Though at BCB frequencies my antenna is much too short, it is actually much too long an antenna at short-wave frequencies. You can probably get by with a lot less, depending on your location.

With these things in mind, let’s begin and take a look at a project that I believe will give you plenty of enjoyment – and will probably raise many questions. In fact, I hope that this article will generate enough interest in short-wave crystal set reception that we see some real innovation in future designs.

The radio is based on the Mystery Crystal Set designed by a fellow who called himself "Proton" and who first published details of the set in the Sunday Mail newspaper in Brisbane, Australia in 1932. I won’t rehash any of the details because the set is well covered in the articles posted at http://www.clarion.org.au/crystalset/mystery.html by Ray Creighton. I have simply adapted the circuit and modified it a bit for my set. Fig. 1 is the basic schematic.

In this configuration, L1 is used as a coupling coil for the antenna and one end is attached to either A or B on the primary. This is a very interesting hookup, more selective than the basic circuit in Fig. 1, but not quite as sensitive. With L1 hooked up to point A, the selectivity is quite sharp. When hooked to point B, the set is so selective that tuning can be tedious. Again, the ground is optional, but I find a little better sensitivity in this hookup with the ground connected and the selectivity hardly suffers at all. One thing to try would be to decrease the spacing between L1 and L2/L3. I think that the current spacing may result in coupling that is a bit too loose for this set.
The configuration detailed in Figure 4 shows some promise for daytime reception in the upper short-wave bands and for further development as a set with variable coupling. With the existing design, the coupling between L1 and L2/L3 is somewhat loose at the ½ inch spacing. Making L1 moveable and possibly large enough to fit over L2/L3 are some things I am considering.

Construction

The coil form is a 2.5 inch long piece of 2" white PVC plumbing pipe with an outside diameter of 2 3/8 inches. This is the kind that has a thickness of about 3/16 inches and is known as "Schedule 40". Construction details are shown in Figure 2.

L1 – 20 turns #22 close wound, approx. 35 uH

L2 – 13 turns #18 or #20 wound at 20 tpi, approx. 12 uH

L3 – 6 turns #22 bifilar wound in the center of L2

C1 – I’ve been using a 20 – 56 pF air variable for coverage of approx. 6 – 10 MHz and a 13 – 250 pF air variable for approx. 2.9 – 12.7 MHz coverage with the coils shown.

Diode – 1N34A or crystal detector.

(You may find as I did that a piece of pyrite and a cats whisker work much better than a diode. For some reason, I find that the pyrite detector is more sensitive and gives me much better volume than the diode. Also, with pyrite, you can eliminate the resistor across the crystal earplug.)

Resistor – 47K (*Note: you can eliminate this resistor if you are using high impedance magnetic headphones)

Phones – crystal earplug or high impedance magnetic phones

I have been using alligator leads to connect it up so I can rapidly change configurations. The photo shown at the beginning of this article is a completed homebrew version of the set that uses mostly non-electronic parts (except for one Fahnestock clip hat was used to hold the detector rod). The capacitor is made from a plastic tube and some aluminum tape that you can find at auto parts stores.

In the original coil I wound, I used hot-melt glue to hold the windings in place. About six beads or "ribs" across each of the windings works very well. Also looks pretty good – better than tape!

In the basic "mystery" circuit shown in Fig. 1, L1 is not used. The tuned primary (L2) has two antenna connection points, A and B. A is the least selective, but gives a louder signal. B is more selective, but the sensitivity drops notably. While I show a ground connection, I noticed that results vary. In most cases, I find that the set works better in this configuration without a ground and is very sensitive. Selectivity is enhanced with the ground connected, but some signals drop out while others get louder. I’m not sure why this is and I’m still experimenting. I have tried putting a small trimmer capacitor in the ground connection to vary the coupling to ground, but my results are inconclusive at this point.

Overall, the basic configuration works very well and is a fine set in its own right. I easily pick up WWCR at 5070 kHz, WEWM on 9975 kHz, have heard Radio Havana (Cuba), the BBC and many other German, Chinese, French and Spanish language broadcasts. My first night, I picked up a station that was running a program called "Let’s Learn Chinese". Bear in mind that propagation conditions vary considerably. You may or may not hear this much at first. Then again, you may hear even more. Some evenings I hear very little but I’m listening as I work on this article in late February and there seems to be stations everywhere as I tune. The audible stations fade in and out and back again, so I get a good variety without having to touch the tuning dial!

As I mentioned earlier, in my location near Cincinnati, Ohio, I have a 50 kW blowtorch, WSAI on 1530 kHz, virtually in my backyard. I have to use a wave trap to tune this station out or it’s all I hear. As a matter of fact, I can hook a diode up to a crystal earplug, hold the diode in my hand and still hear this station loudly! My point is that your conditions will certainly be different than mine, so there is no way I can tell you what to expect to hear. But I can almost guarantee that you will hear something.

Figure 3 shows another configuration I have tried.

In this configuration, L1 is used as a coupling coil for the antenna and one end is attached to either A or B on the primary. This is a very interesting hookup, more selective than the basic circuit in Fig. 1, but not quite as sensitive. With L1 hooked up to point A, the selectivity is quite sharp. When hooked to point B, the set is so selective that tuning can be tedious. Again, the ground is optional, but I find a little better sensitivity in this hookup with the ground connected and the selectivity hardly suffers at all. One thing to try would be to decrease the spacing between L1 and L2/L3. I think that the current spacing may result in coupling that is a bit too loose for this set.

The configuration detailed in Figure 4 shows some promise for daytime reception in the upper short-wave bands and for further development as a set with variable coupling. With the existing design, the coupling between L1 and L2/L3 is somewhat loose at the ½ inch spacing. Making L1 moveable and possibly large enough to fit over L2/L3 are some things I am considering.

Here are some ideas for further experimentation.

Grounding connections A and B to see how this affects reception. (This would actually be defeating the mystery circuit and using L3 as just a detector-coupling coil)
Hook up a variable capacitor in series with the antenna.
Hook up a variable capacitor in parallel across L1 to tune the antenna.
Try the "Tuggle" circuit across L2. This would involve using a 2-gang variable capacitor and hooking one of the sections in parallel with L2 and the other section in series with the ground.
Try the Tuggle circuit across L1.
Use Tuggle tuning with main variable section across L1 and the second capacitor section in series with A/B connection.
Make L1 moveable to vary coupling.
Band switching and band spreading using various fixed and variable caps.
Use a smaller coil form to approximate a 1:1 length-diameter ratio.
Use a smaller inductance value (same as L2?) for L1.
This is by no means a complete list of the things that can be tried with this circuit. In fact, I even redesigned the coil to the following dimensions:

L2 – 18 turns #20 space wound to 1.3" long, 2.375" diameter for approx. 20 uH.

L3 – 7 turns 7/30* bunched cable bifilar wound in center of L2

L1 is not present in this configuration.

*7/30 cable is 7 strands #30 enameled wire twisted into a cable of approx. size of #20. Individual wires are stripped at the ends then twisted together and tinned.

I hope I have given you some food for thought and inspired you to try your hand at making this interesting circuit work. I intend to continue my own experiments and perhaps write another article at some future time. If you want to contact me, you can post a message on Rap-n-Tap, the Yahoo Crystal Set Radio Club, or email me at kc4iwt@yahoo.com. I welcome all comments and suggestions.

Good luck and Happy Experimenting!

3/18/2001 Notes on further modifications

L1 is now present again on the redesigned coil. It comprises 8 turns of # 22 AWG close wound, spaced ¼" from the bottom end of L2. The antenna and ground connections are made to this coil.

L2 is now 14 turns instead of 18 turns to bring the coil more in range of the most active SW bands.

L3 is unchanged.

Experiments with a Perikon detector are very interesting. My Perikon detector consists of a piece of chalcopyrite in contact with a small cone-shaped piece of zincite. It is equally as sensitive as my pyrite detector – maybe more so under some conditions – and has an interesting property in that it appears to be somewhat "tunable". I’m not sure if this is due to signal strength or has more to do with the frequency to which the set is tuned, but I observe a distinct ability to peak signals differently as I tune across the bands. I seem to recall some mention of this property in early radio literature.

One big advantage of the Perikon is that it is not as touchy as the typical catswhisker-and-mineral detector. It is easy to begin detecting a signal and once detection begins, it is a simple matter to peak the signal. I also observe that the Perikon requires a bit of pressure to work properly. It doesn’t require the light touch like other point contact detectors and adjustment is non-critical. Unlike the catswhisker detector, the Perikon doesn’t mind being bumped and tends to keep its setting. It is very stable. I like this detector a lot.

I tried a zincite/pyrite combination, but you can forget that one. Just doesn’t work. Likewise, chalcopyrite with a catswhisker just isn’t very sensitive. It works, but it seems to been just a couple of steps up from a rusty razor blade. Yes, the razor blade detector actually works on this set on some of the stronger signals. And I have to say again that a 1N34 germanium diode just lacks sensitivity in this set. It doesn’t work as well as either the Perikon or the pyrite detectors.

Source: http://www.qsl.net/kc4iwt/xtal/SWMystery.htm

Zenith K731

2010-06-17T22:38:00.000-07:00

Made up of 8 valves

Medium Wave/FM

Magnetic Loop Antenna

Induction Coupled Antenna ((One the right with white and blue wires))

Model of 1950

Tactical Antennas

2010-05-19T22:07:00.000-07:00

Critical Tasks: 01-5705.07-0003
01-5879.07.9001

OVERVIEW

LESSON DESCRIPTION:

In this lesson, you will learn about the types of tactical antennas and their radiation patterns. In addition, you will learn about fabricating field expedient antennas using various repair techniques.

TERMINAL LEARNING OBJECTIVE

ACTION:	Explain basic antenna theory.
CONDITION:	Given this lesson.
STANDARD:	To demonstrate competence, you must achieve a minimum of 70 percent on the subcourse examination.
REFERENCES:	The material in this lesson was derived from FM 11-32, FM 11-64, FM 24-18, FM 24-19, and TC 24-24.

INTRODUCTION

Tactical antennas are designed for efficiency and ease-of-use, and are ruggedized to take the abuse they receive in the field. Some antennas are easy to use, such as a whip antenna that is used in high mobility operations. Others, like directional antennas, require a working knowledge of antenna engineering. All antennas either release or capture electromagnetic radiation.

1. General. Most practical transmitting antennas are divided into two basic classifications-half-wave antennas and quarter-wave antennas. An antenna operates some distance above the ground and may be polarized either vertically or horizontally. A quarter-wave antenna operates with one end grounded. Quarter-wave antennas are used both below and above 2 MHz. Half-wave antennas are used at the higher frequencies (above 2 MHz).

2. Half-wave antenna. The half-wave antenna operates on the principle that the wavelength to which any wire will electrically tune depends upon its physical length. It is center-fed. Its total wire length equals a half of the wavelength of the signal to be transmitted. The maximum radiation emanates perpendicular from the axis to the half-wave antenna. The half-wave antenna is also known as a doublet, a dipole, or a Hertz antenna. It can be erected in a vertical, horizontal, or slanting position between trees or with upright supports from a kit. The half-wave antenna is used for voice or RATT messages when the tactical situation permit stationary operation. It is used for operating in the 2-to 30-MHz frequency range, and it extends the signal range to 300 miles and beyond by using sky wave propagation. The half-wave antenna operates at high frequencies when used on an aircraft or vehicle. In such cases the aircraft or vehicle chassis becomes the effective ground for the antenna. The AN/GRA-50 antenna group that is used in erecting a half-wave system is shown in Figure 2-1. Two configurations for the AN/GRA-50 half-wave antenna are shown in Figures 2-2 and 2-3.

Figure 2-1. AN/GRA-50 antenna group

Figure 2-2. Half-wave doublet antenna with two upright supports

Figure 2-3. Half-wave doublet antenna supported by trees

3. Whip antenna. The efficient half-wave antenna is not practical for use in mobile operations, particularly with vehicular-mounted radio set. The whip is the most common antenna used for both manpack and mobile vehicle operations. It is electrically short and vertically positioned. To achieve an efficiency comparable to that of a half-wave antenna, the height of the vertical radiator should be a quarter wavelength. To attain this, a loaded whip is used. This loading increases the electrical length of the vertical radiator to a quarter wavelength. The other quarter wavelength of the antenna is supplied by the ground, a counterpoise, or any conducting surface that is large enough. Some common whip antenna applications are shown in Figure 2-4.

Figure 2-4. Whip antennas

a. Whip antennas used with HF tactical radio sets can be as long as 15 feet, such as the whip used on a RATT rig. The whip antenna provides an omnidirectional pattern during mobile operations. When the RATT rig arrives at its destination, its crew switches to the half-wave antenna.

b. The whip antenna used with lightweight portable FM radios is 3 ft long for the semi-rigid steel tape antenna and 10 ft long for the multisection whip antenna. It is shorter than a quarter wavelength to keep it at a practical length. (A quarter wavelength antenna for 5 MHz would be over 46 feet long.) An antenna tuning unit, built into the radio set or supplied with it, compensates for the missing antenna length. The tuning unit (called a matching unit when mounted on the antenna) varies the electrical length of the antenna to accommodate a range of frequencies.

c. The whip antennas used with tactical radio sets radiate an omnidirectional pattern in the horizontal plane. This radiation pattern is ideal for tactical operations because the stations in a radio net will lie in random directions and will frequently change their positions.

d. When a whip antenna is mounted on a vehicle, the metal of the vehicle affects antenna's operation. As a result, the direction in which the vehicle is facing may affect transmission and reception, particularly of distant or weak signals. A vehicle with a whip antenna mounted on the left rear side transmits its strongest signal in a line running from the antenna through the right front side of the vehicle. Likewise, an antenna mounted on the right rear side of the vehicle transmits its strongest signal in a direction toward the left front side. The best reception is obtained from signals traveling in the direction shown by the dashed arrows in Figure 2-5.

Figure 2-5. Best directivity of whip antenna mounted on vehicle

e. The best direction for transmission can often be determined by driving the vehicle in a small circle until the best position is located. Normally, the best reception and transmission are achieved in the same direction.

4. Ground-plane antenna. This antenna is a vertical quarter-wave antenna that is used to increase the transmission and reception range of tactical FM radio sets. It uses radial elements (acting as a counterpoise) that serve as the ground. The coaxial cable is connected with the inner conductor feeding the vertical element, and the braid of the coaxial cable is connected to the radials (the ground-plane) to keep them at ground potential. The ground-plane antenna is a broad-tuned type that radiates efficiently over a wide range of frequencies. The two tactical ground-plane antennas in wide use throughout the US Army are the RC-292 and the OE-254.

a. The RC-292 is a stationary, general-purpose, ground-plane antenna. The vertical radiating element and the ground-plane elements must be changed to the proper length for different operating frequencies. Its frequency range is between 20 and 76 MHz, and its planning range is about twice that of a radio set using a quarter-wave whip antenna. The RC-292 antenna can be erected at various heights up to 41 feet, depending on the number of mast sections used. Figure 2-6 shows an erected RC-292 antenna.

Figure 2-6. RC-292 ground-plane antenna

b. The OE-254 broadband, omnidirectional VHF antenna system is replacing the RC-292. The OE-254 antenna operates in the 30-to 88-MHz frequency range without the need to manually drop and change out antenna elements. Its planning range is about 36 miles for average terrain. Like the RC-292, the OE-254 can be erected at different heights, depending on the number of mast section used. An erected OE-254 is depicted in Figure 2-7.

Figure 2-7. OE-254 ground-plane antenna

5. Directional VHF log-periodic antenna.

a. This broadband, omnidirectional antenna provides an extended range and directivity for tactical radios. It is used to communicate in the 30-to 88-MHz frequency range and does not require any mechanical or electrical adjustments.

b. The log-periodic antenna can operate with either horizontal or vertical polarization. It has the capability of changing polarization in less than one minute.

c. The highly directional radiation pattern of the log-periodic antenna provides very effective electronic counter-countermeasures (ECCM) in a hostile electronic warfare (EW) environment. Since its radiated energy is focused in one direction, less transmitter power is needed, further enhancing ECCM.

d. This antenna can be erected in a geographical area no greater than 60 feet in diameter by two soldiers in 20 minutes. Its mechanical azimuth can be changed within one minute. This antenna can be mounted on a quick-erect mast either on a vehicle or a shelter, and transported by manpack or tactical vehicle when fitted into two packages (one for the antenna and one for the mast).

e. The log-periodic antenna is organic to battalion and higher level units for special applications. It is primarily used by forward units in command and intelligence nets to a higher headquarters. Because it is a directional antenna, its use is usually restricted to point-to-point communications.

f. Figure 2-8 illustrates the log-periodic antenna in three configurations.

Figure 2-8. Log-periodic antenna

6. VHF half-rhombic antenna OE-303.

a. The half-rhombic antenna is used mostly for special purposes by forward units over extended distances on command and control and intelligence nets. The OE-303 antenna is a vertically polarized antenna which, when used with the current VHF-FM tactical radios, considerably extends the transmission range. It provides some degree of ECCM protection not offered by the current VHF-FM omnidirectional antenna. When properly employed, the half-rhombic antenna decreases VHF-FM radio susceptibility to hostile EW operations and enhances the communications ranges of the deployed radio set. This effect is realized by directing the maximum signal strength in the direction of the desired friendly unit.

b. This high-gain, lightweight, directional antenna is capable of operating in the 30-to 88-MHz frequency range without having to be physically tuned by the operator. Its highly directional pattern makes it especially suited in providing point-to-point communications. It is oriented in the direction of the desired transmission by using a compass and the appropriate map sheet.

c. The OE-303 antenna is rugged enough to withstand moving (erection and teardown) every four to six hours. It can operate in harsh climatic conditions. It can be erected by two soldiers in 20 minutes or less in a geographical area 175 ft in diameter or less, depending on the frequency used. This antenna can be mounted on any structure about 50 feet in height, and is capable of azimuth directional change within one minute. Mast assembly AB-1244 is the primary antenna support structure used with the half-rhombic VHF antenna. Using its mast assembly, this antenna is 30 feet high.

d. The antenna and all the ancillary equipment (guys, stakes, tools, mast sections) are contained in two carrying bags for manpack or vehicular transportation. Figure 2-9 depicts the half-rhombic antenna.

Figure 2-9. Half-rhombic VHF antenna

7. Near vertical incidence sky wave (NVIS). NVIS antenna AS-2259/GR is a lightweight sloping dipole, omnidirectional antenna used with AM radios (AN/GRC-106) and improved high frequency radios (IHFR)(AN/PRC-104A and AN/GRC-213/193A) that operate in the HF range of 2 to 30 MHz. Like the doublet antenna, the NVIS is used when the tactical situation allows stationary operations. The NVIS extends radio range up to 300 miles by using sky wave propagation. Polarized horizontally and vertically at the same time, it can be erected by two soldiers in about five minuets. Figure 2-10 shows an operator using an NVIS antenna wit an AN/PRC-104A portable radio.

Figure 2-10. NVIS antenna

8. Combat net radio (CNR). CNR is designed around three separate radio systems--IHFR, Single-Channel Ground and Airborne Radio System (SINCGARS), and single-channel tactical satellite (TACSAT) radios.

a. The IHFR is replacing the older HF manpack (AN/PRC-70/74) and vehicular (AN/GRC-106) radios. User-owned and operated, it employs both ground and sky wave propagation for short and medium-range communications to pass voice and data signals. The IHFR uses the manpacked whip antenna, the vehicle-mounted whip antenna, the AN/GRA-50 doublet antenna, and the AS-2259 NVIS antenna.

(1) The AT-271A/PRC, one type of collapsible whip antenna for manpack operation, is depicted in Figure 2-11. This antenna is easily assembled and broken down. The cord running through the sections provides the tension needed to keep them together.

Figure 2-11. Collapsible whip antenna AT-271A/PRC with antenna base

(2) The AS-3683/PRC, another whip antenna used with the AN/PRC-104A and the SINCGARS radios, is shown in Figure 2-12. This is a very flexible antenna especially suited for use in thick brush or jungle. Its flexible goose-neck antenna base allows the operator to orient it to obtain optimum reception. However, using the goose neck antenna base is optional.

Figure 2-12. Flexible whip antenna AS-3683/PRC

(3) A whip antenna used with the AN/GRC-213 in a vehicle-mounted configuration is shown in Fig 2-13. When installed with the vehicle installation kit, this antenna is the most convenient to use because it allows communications while the vehicle is moving and it has a omnidirectional (360°) radiation pattern. It also requires no support except for the vehicle mount. A disadvantage is that its propagation range is shorter than either the doublet or NVIS antennas.

Figure 2-13. Vehicle-mounted whip antenna

b. SINCGARS operates in the VHF range.

(1) SINCGARS uses broadband antennas that do not have to be changed when frequencies are changed, such as the OE-254 ground-plane and the AS-3900 and AS-3684 vehicular whip antennas. The output frequency can change in a wide range between hops due to the frequency hopping nature of SINCGARS. The narrow band RC-292 ground-plane antenna cannot be used.

(2) Like the IHFR, SINCGARS uses the manpack whip antenna (AS-3683/PRC) for communicating in heavy vegetation or when the transmitting range is deliberately limited. It also operates using the AS-3684/VRC whip antenna, a 10-foot long antenna that consists of two antenna elements and a matching unit base (Figure 2-14). The base spring allows the antenna to bend when it strikes an obstruction

Figure 2-14. AS-3684/VRC vehicular antenna

c. TACSAT operates in the UHF range. The AN/PSC-3 and AN/VSC-7 communications systems are lightweight, highly compact, and deployable in quick-reaction situations where extended communication range is essential to mission effectiveness. They can operate on-the-move/line-of-sight (LOS) at 2 watts or in the at-halt/satellite mode at 35 watts. They can transmit or receive in voice or data formats in both modes. Figure 2-15shows the AN/PSC-3 radio set. This medium gain, collapsible parabolic antenna can be set up in minutes and is highly reliable. The AN/VSC-7 TACSAT radio set (Figure 2-16) used as a net control station and is mounted in a tactical truck or an S-280 communications shelter. It can serve up to 15 AN/PSC-3 terminals in a communications net with the selection of conference or individual call-codes. Its low-gain omnidirectional whip antenna provides LOS. The AN/VSC-7's high-gain antenna enhances transmission and reception.

Figure 2-15. AN/PSC-3 TACSAT radio set

Figure 2-16. AN/VSC-7 TACSAT radio set

9. UHF antennas. These highly directional antennas are used with mobile subscriber equipment (MSE) and the older multichannel systems. They concentrate radiation in a given direction and minimize radiation in other directions. Their high directivity also aids in obtaining a slight degree of transmission security, making enemy direction finding more difficult, and reducing noise and interference.

a. The corner-reflector (flyswatter) antenna consists of an adjustable reflector and an antenna element. It is used in multichannel systems with radios that operate in the 200-to 1000-MHz range. Highly directional, its reflector angle can be adjusted to operate on any frequency within its range. This antenna is usually used with radio sets that have RF duplexing capabilities. The RF duplexer permits the radio set to transmit and receive, using one coaxial cable between the antenna and the radio set. The corner-reflector is shown is both vertical and horizontal polarization positions in Figure 2-17.

Figure 2-17. Typical corner reflector antenna

b. The horn-type antenna is a directional antenna with a modified dipole element mounted in a ridge-loaded horn. The horn-type antenna used in multichannel systems are pyramidal (rectangular and flared in both planes). The horn is designed to get the flare, length, and aperture that will give the best performance throughout the horn's entire frequency range. This combination of flare, length, and aperture emits a narrow beam of high-intensity RF energy in the forward direction. Horn antennas can be vertically or horizontally polarized, and can be mounted in pairs on the same mast or singularly on separate masts. When used with a radio set having an RF duplex, a single horn can be used to transmit and receive radio signals. Horn-type antennas are used with some radio sets that operate on frequencies from 601.5 to 1849.5 MHz. The horn antenna is broadband and no adjustments are made when changing frequencies. Elevation or depression angles may be made at the antenna's rear, as needed. A rear view of a pair of horn-type antennas mounted in a vertical polarization is shown in Figure 2-18.

Figure 2-18. Typical horn-type antenna

c. The parabolic reflector antenna consists of a saucer-like reflecting surface (parabola) and a dipole (feed device) placed at its focal point. There are numerous types of reflector antennas used, depending on the frequency. The MSE LOS radios use parabolic reflector antennas mounted on 15-meter masts. Figure 2-19 shows two examples of parabolic antennas.

Figure 2-19. Parabolic reflector antennas

10. Field repair and expedients. Antennas are sometimes broken or damaged, resulting in failed or poor communications. In the days before cable television, viewers at home received a TV signal through an antenna, either strapped to the chimney or sitting on top of the set. If the antenna was missing or broken, an expedient loop antenna could be fashioned from a simple coat hanger. Reception was not the best, but it was tolerable. Remember, as a signal officer, your job is to get the message through. Knowing how to do a field expedient repair job may come in handy some day. The following antenna repair techniques have been proven to work.

a. Metallic whip antennas.

(1) Should a whip antenna break into two sections, you can lash the two sections together to provide a good mechanical connection. To ensure essential electrical conductivity, scrape the paint off of each section's end and tie them together with stripped field wire (WD-1). Solder the connection if you have the time and equipment. Place a stick, pole, or branch on each side of the break and wrap the splint tightly with field wire, rope, or tape, as shown in Figure 2-20.

Figure 2-20. Spliced metallic whip antenna

(2) If you lose your antenna and are left with just a stub, you can use another repair method to get back on the air. If the missing section is about 6 feet long, just find a pole the same length and lash it to the stub. Scrape off the paint from the top 2 inches of the whip's stub and wrap about 12 inches of bare wire around the stub's scraped portion. Wrap it tight and tape it securely. Attach a length of WD-1 along the pole's length with tape. The total length of the upright WD-1 and antenna stub should be the same length as the length of the original antenna. This antenna will not take much abuse, but it will send and receive signals. Figure 2-21 illustrates this technique.

Figure 2-21. Spliced metallic whip antenna using WD-1 as part of the antenna

b. Vertical antennas transmit and receive omnidirectionally. Most tactical antennas used for vehicular and manpack radios are vertical. A vertical antenna can be improvised by using a metal pipe or rod of the correct length, held erect by guy lines. The antenna's lower end is insulated from ground by placing it on insulating material. Figure 2-22 shows vertical antennas made of wire and supported by a tree and a wooden pole. If the vertical mast is not long enough to support the wire upright, the connection can be modified at the antenna's top, as shown in Figure 2-23.

Figure 2-22. Field substitutes for support of vertical wire antennas

Figure 2-23. Additional means of supporting vertical wire antennas

c. The electrical length of an end-fed, half-wave antenna is measured from the antenna terminal on the radio set to the antenna's far end. For optimum performance, the antenna should be constructed longer than necessary, and shortened as required until the best results are achieved. The ground terminal of the radio set should be connected to a good Earth ground for this antenna to operate efficiently. This antenna is depicted in Figure 2-24.

Figure 2-24. End-fed half-wave antenna

d. The center-fed doublet antenna is a half-wave antenna consisting of two quarter-wavelength sections on each side of the center (Figure 2-25). Doublet antennas are directional broadside to their length; this makes the vertical doublet antenna essentially omnidirectional. The horizontal doublet antenna is bidirectional. A center-fed half-wave FM antenna can be supported by a wooden frame, shown in Figure 2-26. View A shows a horizontal antenna, and view B shows a vertical antenna. These antennas can be rotated to any position to obtain the best performance. If the antenna is erected vertically, the transmission line should be brought out horizontally from the antenna for a distance equal to at least one-half of the antenna's length before it is dropped down to the radio set.

Figure 2-25. Half-wave doublet antenna

Figure 2-26. Center-fed half-wave antenna

e. Two field-expedient directional antennas are the vertical half-rhombic antenna (Figure 2-27) and the long-wire antenna (Figure 2-28). These antennas consist of a single wire, preferably two or more wavelengths long, supported on poles at a height of 3 to 7 meters (10 to 20 feet) above the ground. If needed, the antennas will operate satisfactorily as low as 1 meter (about 3 feet) above the ground. The wire's far end is connected to ground through a noninductive 500-to 600-ohm resistor. To ensure that the transmitter's output power will not burn out the resistor, a resistor rated at least one-half of the transmitter's wattage output should be used. A reasonably good ground, such as a number of ground rods or a counterpoise, should be used at both ends of the antenna. The radiation pattern is directional. These antennas are used primarily for transmitting or receiving HF signals.

Figure 2-27. Vertical half-rhombic antenna

Figure 2-28. Long-wire antenna

f.The V antenna

(1) This antenna consists of two wires forming a V, with the open area of the V pointing toward the desired direction of transmission or reception (Figure 2-29). An easier way of constructing this antenna is to slope the legs downward from the apex of the V; this is called a sloping-V antenna (Figure 2-30).

Figure 2-29. V antenna

Figure 2-30. Sloping-V antenna

(2) The angle between the legs varies with the length of the legs in order to achieve minimum performance. Table 2-1 can be used to determine the angle and the length of the legs.

Table 2-1. Leg angle for V antennas

(3) When this antenna is used with more than one frequency or wavelength, an apex angle is used that is midway between the extreme angles determined by the chart.

(4) To make the V antenna radiate in only one direction, noninductive terminating resistors are added from the end of each leg (not at the apex) to ground. The resistors should be approximately 500 ohms and have a power rating at least half that of the output power of the transmitter being used. The antenna will radiate bidirectionally, both front and back without the resistors.

11. Safety. Soldiers are still occasionally killed or seriously injured a result of antenna accident, in spite of repeated safety warnings tough briefings, publications, and messages. As a signal officer, you should develop a keen sense of field safety, especially as it relates to signal operations. If you know an antenna is too close to a power line, insist that it be dropped and moved. Safety tips and warnings that are found in many signal-related publications are shown in Figures 2-31 and 2-32, respectively. Study these safety tips and warnings and think back to experiences you have had during previous operations. Have you violated any of these warnings? If the answer is no, you are to be commended for your good approach to safety. If the answer is yes, then resolve to heed the warnings henceforth.

Figure 2-31. Safety tips

Figure 2-32. Safety warning

12. Summary. In this lesson, you learned about the types of tactical antennas, their radiation patterns, and how to fabricate field-expedient antennas using various repair techniques.

a. The half-wave antenna is also called a doublet, a dipole, or a Hertz antenna. It is center-fed. Its total wire length is one half of the wavelength of the signal to be transmitted.

b. The whip antenna provides an omnidirectional radiation pattern. It is a quarter-wave antenna used for manpack and vehicular operations.

c. The ground-plane antenna is a vertical quarter-wave antenna that increases the range of tactical FM radio sets. Its radial elements provide a counterpoise that simulates a ground. The older RC-292 has radial elements that must be changed accordingly with frequency changes. The OE-254 does not require any changes in elements when frequencies change.

d. The log-periodic antenna is very directional and is usually used in point-to-point communications.

e. The half-rhombic antenna OE-303 provides an extended range and affords some ECCM protection (not omnidirectional).

f. The NVIS is a sloping dipole that gives an omnidirectional pattern for AM radios. It can extend the range up to 300 miles.

g. The two CNR antennas are the AT-271A/PRC, a collapsible whip for manpack operations, and the AS-3683/PRC, a flexible antenna used in areas of heavy vegetation.

h. The three SINCGARS antennas are the OE-254, the AS-3684/VRC (vehicular mounted), and the AS-3683/PRC.

i. The two TACSAT antennas are the collapsible parabolic reflector for the AN/PSC-3 and the omnidirectional whip antenna for the AN/VSC-7.

j. There are several UHF antennas.

(1) The corner-reflector (flyswatter) antenna is highly directional and is used with multichannel systems.

(2) The horn-type antenna is another antenna used in multichannel systems. The flared design serves to direct the RF energy in a highly directional pattern.

(3) The parabolic reflector antenna has a reflecting surface and a dipole at its center. The reflector is used to capture or release signals.

k. There are several field expedient antennas.

(1) Metallic whip. Broken whips can be lashed together using WD-1, rope, and tape. If part of the antennas is missing, field wire can be used as the radiating element.

(2) Directional antennas. The vertical half-rhombic and the long-wire antennas are used for transmitting and receiving HF signals.

(3) V antenna. It is made of two wires forming a V with the open end pointing toward the direction of transmission. Using a resistor changes the V antenna from bidirectional to unidirectional.

Source: http://www.globalsecurity.org/military/library/policy/army/accp/ss0131/lsn2.htm

SW Receiver_Superegen_3T_SSB

2010-03-08T18:12:00.000-08:00

Jurjen Kranenborg, January 2003 (revised December 2003)

http://www.kranenborg.org/ee

{Please contact me via my website if you find this page interesting and have built the receiver yourself: I am interested in your experiences. I gratefully thank Tor Gjerde for his support in publishing this document on the Internet}

Summary

This article describes a small
I made to the EE2003 Short Wave (SW) receiver that turns it into a simple but sensitive and user-friendly world receiver. This so-called regenerative receiver can be used for both general short wave listening on the 49m, 41m and 31m AM-type broadcast bands, as well as for SSB (Single Side-Band) reception of amateur and marine/aircraft stations. The major change is the addition of regeneration control which allows the receiver to be tuned for optimal sensitivity/selectivity for the complete frequency range (5.8 – 10MHz) as well as the addition (for SSB reception) or removal (for broadcast reception) of the regeneration “beat-note” frequency. With this design, I have received - from my home location in the Netherlands - several distant broadcast stations like All India Radio, Radio Yerevan (Armenia), Radio Bangkok, Radio Tokyo, Australia etc. and various European SSB amateur stations without using an external antenna.

Background

About two years ago I re-discovered my Philips kits (the set now consists of the complete EE2000 and EE2001 series) and revived the electronics hobby after a period of almost twenty years. Since I am particularly interested in receiver designs, I built most of them again, and so I came across the EE2003 SW receiver (nr. 5.03). The manual mentions that it is a so-called superregenerative or “superreg” design (although seemingly a very simple circuit it is actually quite difficult to understand, see Ref.1 for a thorough explanation). A key feature of superregs is the very high amplification factor (over 100,000), which causes the typical noise or “hiss” that can be heard when the receiver is not tuned in to a particular station, the noise being caused by thermal fluctuations generated in the receiver front-end components.

Although the original receiver did work it had two pecularities: a) the receiver was “deaf” at higher frequencies while oscillations associated with radio stations abounded in the lower frequency region, b) the receiver did not produce the “hiss” that is typical of superreg designs (for example, the FM receivers of EE2010/EE2013 clearly do). The oscillations that can be heard while tuning in to stations are typical of regenerative receivers, where part of the amplified RF signal is fed back into the RF stage, which leads to the oscillations mentioned before if the amount of feedback is relatively large.

To investigate the behaviour of the receiver I decided to replace the fixed 22K resistor (R4) with a 47K trimming potentiometer in series with a protective 4,7K resistor, expecting that this would allow to a superreg type of behaviour. Instead, it appeared that this new configuration controlled the amount of feedback (by controlling the T1 emitter-collector voltage difference), and allowed for a setting just below the onset of oscillation. In that case the regenerative receiver has maximum sensitivity and selectivity for AM type (broadcast) stations. When in the oscillating mode (i.e. strong feedback), the receiver itself provides for the carrier signal that is needed to demodulate stations of the so-called SSB (Single Side-Band) type, which encompasses most of the amateur, marine and aircraft stations. Since the amount of feedback (and thus the boundary between the oscillating and non-oscillating regimes) depends on the frequency, both the tuning capacitor and the regeneration trimmer have to be adjusted when one travels the frequency band. After some experimentation and the addition of a few components, I derived appropriate values for some components that allow for listening to both AM and SSB signals over the complete frequency range of the receiver. Note that with this regenerative receiver design the Philips EE2000 series now covers all receiver concepts: diode, reflex, regenerative, superregenerative, and superheterodyne.

In the section below this design is presented, with clear indications of the diferences between the original design. Subsequently, I describe some tuning practices as well as the kinds of stations that can be received within the frequency range. I conclude with some examples and design issues which became apparent in my design.

Design

The figure above shows a schematic diagram of the receiver. A red color denotes a newly added component, a green one indicates a change of value for an existing component. The latter has been done to allow the three shortwave broadcast bands to be in the tuning range without the need for bandswitching. The extra components can be easily added to the original construction diagram in the EE2003 manual.

The following changes and additions have been made (with refs to the original component numbers):

1. The main coil: Used to be 8 windings in the center of the ferrite rod; now becomes 9 turns near the edge (see the photographs at the end of this document). This change was made to allow for the desired tuning range.

2. C1 (at the base of T1): used to be 0.1uF (Polyester), now changed to at least 10uF to prevent slow oscillation of the system that prevents proper functioning.

3. C2: Used to be 47 pF, now increased to 100pF, to allow for sufficient regeneration at low frequencies (T1 is used as a common-base amplifier with fixed regeneration feedback through C2 !).

4. C4: Used to be 10 pF, now lowered to 2.7 pF or even smaller to allow reception of the full 31m band. This value is not standard in the EE-series, so you may well remove C4 if you dont have such a small valued capacitor.

5. R4: Used to be 22K, now becomes 150K. This resistor influences the “spread” in regeneration control.

6. C6: Used to be 4,7uF, now becomes 0.22uF (Polyester).

7. NEW: I added a 100uF (or even larger) capacitor for undisturbed reception of stronger stations. Without this capacitor the receiver tends to “motorboat” even at average volume levels.

8. NEW: In series with the main tuning capacitor I added a 150p capacitor (or using 100pF + 47pF in parallel) for a proper tuning range (without this change the regeneration level remains to low at low frequencies).

9. NEW: In parallel to the main tuning capacitor I added a second, fine-tuning capacitor (I used the EE2005 double variable capacitor in series with a small 10pF capacitor). This greatly increases tuning satisfaction and therefore is strongly recommended! In case you don’t have a second variable capacitor but do have the BB110 varactor (from EE2010/2013), you may use the latter in series with a 10p of 22p capacitor as well.

10. NEW: A 47K regeneration control potmeter has been added for regeneration control. Since the regeneration control should be quite accurate, use a high-quality potmeter (I bought a new one and mounted it into the console). I added a 1uF capacitor also to have real smooth control; its value is not critical, but should probably not be larger than 4,7uF and at least amount to 0.1uF.

11. NEW: A parallel combination of a 100K and 47K resistor in series with the regeneration potmeter provided for a proper regeneration range.

Note that the regeneration control part is outside the RF part of the circuit (as opposed to most other regenerative designs) because the RF choke coil separates them. Practically, this implies that long leads may be used to connect to the regen potmeter, and allows it to be part of the console (in my case, but you may also use the 47K trimming pots of for example EE2004/2010/2014 etc.).

Since the regeneration level depends on the T1 collector-emitter voltage difference, the regeneration level depends on the battery voltage as well. When the batteries get somewhat exhausted you will arrive at a point where you have to replace the 100K-47K combination with a 33K or even 22K resistor.

An alternative design (appropriate for owners of one the EE2001 series kits) uses a more modern LF part which consists of two operational amplifiers; it is almost identical to the LF part of the EE2010/2013 FM receiver. The circuit diagram is printed below. This is the version I implemented, several photographs of the construction are given at the end of this document.

Based on this design I built the receiver several times; in total it was "alive" for more than a year because it performed so well!

Construction Diagrams

The construction diagrams for both receiver versions are given below and were generated by Tor Gjerde. On my website links to PDF versions of the constructions are given, which can be printed and used directly on the breadboard (it should be printed in exactly the same size, no scaling to fit the paper).

Practical Use

Tuning frequency range overview

The tuning range of the regenerative receiver covers three important short wave broadcast bands (49m, 41m and 31m) as well as some SSB amateur (40m) and maritime/aircraft (35m, 45m) bands. For the broadcast bands the best reception conditions are met at a few hours before sunset till a few hours after sunset. However, during spring and summer excellent conditions may sometimes persist until or after midnight for the higher frequencies. During daytime generally only relatively local broadcast stations can be received, as the reflective atmospheric layers are destroyed under influence of the sun. SSB reception is best during daytime, because then these weak stations are not overruled by strong international broadcast stations (of which Russian and Middle-East stations are notorious examples).

An overview of the receiver frequency range is presented in the figure at the left, which depicts the main tuning capacitor dial. At the right side the 49m broadcast band can be found, which contains many strong European stations, as well as stations from the Americas. In the 41m band I located many strong stations which are apparently from the Middle East, in addition to several other interesting stations (like All India Radio, Radio Albania, several Russian stations, some weak unidentified Chinese (?) stations). Late in the evening some Middle-East stations may become very strong and tend to “overrule” the others. The 31m band is very interesting because it contains various distant stations (like Bangkok, Vietnam, Radio Cairo) as well as more near stations, (Yerevan (Armenia), Turkey) but these are also quite difficult to pin down whithout fine-tuning.

The red areas in the dial indicate regions which contain interesting SSB stations, mainly amateurs, although they possibly also contain aircraft and/or maritime stations (35m band). Particularly the 7.0-7.1 MHz interval is filled with several amateur stations from various European countries (Based on my location in the south of the Netherland the German amateurs are particularly strong, but I have also received Dutch, Belgian, French, English and even Italian stations). A fine tuning capacitor is definitely needed to tune to the proper sideband (generally but not exclusively the upper sideband). The SSB signals are very weak, you need maximum volume and your ear in close proximity to the speaker to understand their messages. Best receiving conditions are during daylight; in the late evening and during the night strong (Middle East) broadcast stations overrule the weak SSB signals. Nevertheless, I have received several of them clearly despite their low audio volume (some of them are involved in quite uninteresting discussions about their station equipment, probably in the same way that some men talk about their fancy cars …).

The other two SSB bands are very weak regarding my location (especially the 35m band at 8.5-9 Mhz), I generally had great difficulties with listening to stations. This may however turn out differently on your location.

I want to note that I never have used an external antenna since it did not significantly increase the capabilities of the receiver (in many cases an antenna caused overloading of the receiver by strong broadcast stations and added a lot of background noise). Maybe an antenna helps for SSB stations, but I have no experience in that matter.

Tuning guidelines

If you operate the receiver for the first time, you should check whether you can tune the regeneration level to both AM and SSB reception for the complete frequency range. To do so, take the following steps:

· Turn the main tuning dial (variable capacitor) to the right, tuning in a station on the 49m band, which corresponds to a low frequency. Set the regeneration level at maximum by setting the regeneration potentiometer at the lowest level (R=0). You should hear a loud tone (the beat note) in addition to the station itself. Now decrease the regeneration level (R becomes larger) until you note that the tone dissapears. This should happen at a relatively low regeneration level (R relatively large). In case it happens at a high regeneration level or the beat note cannot be heard at all, decrease the 100K resistor near the trimming potmeter. If the beat note remains at all regeneration levels, the regeneration must be decreased by inreasing the 100K or the 47K resistor in value.

· Set the regeneration level to a maximum (R=0) again. Now turn the tuning dial from the right to the left (highest frequency). As you turn you should hear the oscillations that correspond to the received radio stations. In particular you should note that most of the stations are clustered in three groups, each of the groups corresponding with one of the three broadcast bands. When you arrive at 10MHz, you should still hear the beat notes associated with each station. If the beat note cannot be heard anymore, the regeneration level is still to low even at R=0, and you must decrease the value of the 100K resistor.

· At 10 MHz reduce the regeneration level by increasing the potentiometer resistance. At some point you should note a sudden decrease in noise level (in case you are noted tuned to a station) or the regeneration tone suddenly dissapears (in case you are tuned to a station).

Tuning on a regenerative receiver is a two-handed affair; some experimentation will provide for the best strategy. An appropriate approach is the following:

· Always search from low to high frequency.

· Set the regeneration level at such a level that regeneration occurs, i.e. the beat note can be heard. This will allow you to identify even very weak stations, including SSB and various morsecode stations, and it helps to identify the start of the broadcast bands

· If you have arrived roughly at the appropriate location. reduce the regeneration level to just below the onset of oscillation. With this setting the receiver has maximum sensitivity and selectivity for broadcast (AM) reception. Use fine tuning to tune in to the station of interest. If you change the frequency, also change the regeneration level in order to retain maximum sensitivity.

· In case you want to receive SSB stations, keep the regeneration level high.

The best place to operate this receiver is at the first or second floor of your house.

Station info

Although I will provide for a simple tuning guide in a later update of this document, Ref. 2 provides very useful information on broadcast schemes in the English language (sorted in various ways, for example: time, frequency, country etc.etc.) and various issues and numerous links on shortwave listening. Highly recommended!

An example: my construction

I took some photographs of my receiver to give an impression of the measures I took to secure stable operation.

The picture at the left shows the complete construction. Note that I actually built the design with the opamp amplifier, although the original transistor design should work as well. The two large knobs are for the main frequency tuning and for fine tuning, while the silver knobs are for regeneration control (using a 47K linear potentiometer) and volume control (the original 10K log potentiometer). Note that especially the regeneration potentiometer should be of high quality, since the regeneration level must be adjusted quite accurately for optimal receiver sensitivity and selectivity. To this end I bought a new one, but you may also try the 47K trimming pot of EE2004/2010/2013 etc.

This picture shows the RF part of the receiver. The coil consists of 9 turns which need to be very carefully and closely wound. The red coil is for the antenna and should be immediately adjacent to the main coil. Both coils should be near the end of the ferrite coil. In practice, I never used an antenna. For optimal contact the transistor is mounted upon the components (as is suggested by the Philips manual for the EE2010/13 FM receiver). This is good practice for all designs.

The LF part of the receiver is shown here. It appeared to be good practice to always mount the transistors and ICs upon the components and wires, since this provides for much better contact. Isolated wire is used to fix them. In this way you can even walk around with your receiver without hearing any disturbances.

References

1. E. Insam; Designing Super-Regens, in: Electronics World, April 2002

2. Prime Time Shortwave Guide (www.primetimeshortwave.com)

Source: http://www.kranenborg.org/ee/documents/SWreceiver.doc

THE RADIO BUILDER

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Meter_Voltmeter

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SW_2T_Reflexive

Meter_Bipolar Beta Meter

MW_2T_1D

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Equivalents of Russian Transistors

1. Bipolar transistors

2. Field-effect transistors

3. Analog and digital integrated circuits

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What is a tuned radio frequency TRF receiver?

Reflex Theory

Superhet Theory AM & FM

BACKGROUND TO FM RECEIVER DESIGN

REQUIREMENTS OF AN FM RECEIVER

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V.H.F. RECEPTION

LIMITING ACTION

MEANS OF DETECTION

REVIEW SO FAR AND STEREO RECEPTION

MW_Regen_5T_2 Transformers with tuning circuit

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Transistor Stabalization

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SW_Direct Conversion_3IC

MW_Direct Conversion Reciever_2T_3GeD

The Art Photo

Theory_Direct Conversion Receiver

Direct-conversion receiver

Contents

[edit] Properties

[edit] History and applications

[edit] See also

[edit] External links

Heterodyne

Contents

[edit] Origin and use of term

[edit] How it works