Sunday, October 7, 2012


A Superregen Receiver for FM broadcast or Aircraft band AM reception

February 2004; Revised October 2006 by Rick Andersen

This is the receiver I was bragging about on the radio index page - the receiver that is so sensitive it can hear the local oscillator inside a small transistor radio 30-50 feet away. Build one of these little gems and you will be Able to hear aircraft pilots many miles away with nothing more than a 24 "whip antenna. The Superregenerative detector was popular, in its vacuum tube version, in the early days of VHF reception up through the late 1950's, early '60s. After that, it was found in its transistorized version in simple kits from Radio Shack, etc. It's also the reason for the noisy hissing sound made by the 27 MHz CB Walkie Talkies many of us had as kids. Though a lot of people have not even heard of it, and others think it's obsolete, the fact is that the superregen is still around in a specialized high-frequency applications. Our use of it here is a throwback to the old days when homebrew 'supergennys' were in vogue - as an extremely simple, yet extremely sensitive, broadband VHF receiver that will demodulate FM broadcast stations as well as AM aircraft band transmissions.
In the circuit below, Q1 serves as the superregen detector. Now this configuration is a strange beast, if you're only Casually acquainted with transistor circuit design. First of all, in the original 2004 Embodiment of this circuit, the signal was coupled into the collector circuit of the 2N3904 NPN transistor; Usually we connect the input to the base or emitter, and the collector is Considered to be an "output". Well it turns out that the high impedance of the LC tuned circuit, at the collector, makes it susceptible to outside influence, if we connect an antenna at that point ...... this circuit Teaches us that you can impress a signal on any lead of a transistor and take the output off any other leads, and the damn thing will still work!
In this revised version of Oct.. 2006, I've moved the antenna to the point between the top of the RF choke and the bottom of the emitter of Q1 - the aircraft picks up radio signals even better now than it did before. Again, there are several places where you could couple the signal in.

The tuning is a 15pF variable cap I happened to have lying around in my Junque box; the inductor "L" is nothing but a 2 "piece of # 20 stiff copper wire, bent into a" U "shape. If you squeeze that U into a near-bobby-pin shape, you will have eliminated most of the inductance, raising the frequency of the tuned circuit. You will have to experiment with the amount of "squeezing" you do to the wire; FM broadcast stations (88 - 108 MHz) will need more inductance, and the lower half of the Aircraft band (109-130 MHz approx.) will need less, since it's above the FM broadcast band.
The antenna has been changed from the February 2004 original of this article. Originally I had a 24 "whip, made of # 8 or # 10 solid copper wire, soldered to the ground plane and coupled to the L1 / C-tuning circuit through a 1 pF cap. My prototype was plagued with a lot of" dead spots "and" flutter "as I tuned across the dial. Adding a buffered input stage helped, but I later discovered the present method of making an antenna that worked even better, and allowed me to get rid of that extra input stage, with little change in sensitivity. The antenna is a 24-inch piece of plastic-coated # 20 or # 22 hookup wire, bent in the middle and folded back on itself, then twisted so that we now have a 12-inch "whip" with two connections at the bottom, roomates are soldered between (in series with) the emitter of Q1 and the little 6-turn RF choke that was made by winding # 22 enamelled wire on a BIC pen (the pen is used as a coil form and later removed.) Since very little inductance is wanted at VHF, my folding the antenna wire back on itself and then twisting its two halves together, gives it a "non-inductive" characteristic that Allows me to get 12 "of length without so much inductance as to spoil the circuit's operation around 110-130 MHz. This unusual antenna seems to work very well (plenty of sensitivity) and most of the dead spots and flutter are gone.
Just the make sure you build everything nice and tight - long, floppy leads are a disaster at VHF. I usually use 2 pieces of Radio Shack's 5x7 "copper clad board, connected together perpendicularly so as to make a bottom piece and a vertical front panel - an L-shaped chassis. Then I construct the circuit above this ground plane, using 10 megohm resistors as "standoff insulators" or posts, on top of the roomates I wire the circuit.
Positive feedback required for Oscillation is provided by the small 7PF cap from collector to emitter. You may need to increase of as much as this to the 10-15pF - or, try another transistor, if your detector will not oscillate. The way to tell that your detector is oscillating is to listen for a loud white-noise "rushing" sound from your amplified speakers, connected to the audio output of this radio. If all you hear is "quiet", it is not workin!
Q1's emitter has a 6 turn RF choke connected to it; below that chokes are a 10k resistor to ground and a .001 uf cap across that resistor. These three components form a subcircuit that makes the superregen unique: the Quench Oscillator. (The 10k resistor is also the emitter load across roomates we take roomates audio is sent to the second transistor, Q2, for amplification).
Here's how it works - and I'm giving all this detail Because so many people have no clue about the mysterious goings-on inside this circuit:
The 330K + resistor provides bias to turn Q1 on. The .001 uF cap on the base provides an RF ground at the base. Like a normal regenerative detector, if there is enough positive feedback, the transistor will oscillate. However, in a normal regen, we find that the most sensitive reception Occurs at the point just before Oscillation sets in; after that, we get a heterodyne squeal if there is a carrier present in the signal being received. In a superregen, we interrupt the buildup of feedback, between about 20.000 to 30.000 times per second, with a lower-frequency Sawtooth waveform that is automatically produced in that three-component Mentioned Earlier subcircuit. The .001 uF cap across the 10K resistor forms an RC time-constant circuit that sets the "quenching frequency". It turns out that if we alternately "quench" (interrupt) and then buildup the feedback, at> 20 kHz (above the range of human hearing), we can Effectively drive the transistor much farther into the range where positive feedback would have resulted in self-Oscillation. Ie, by delaying the onset of Oscillation, or chopping it up, we Effectively operate in a much more sensitive region of the transistor's bias. We hear practically down to the "noise floor", and we get fantastic sensitivity.
The drawbacks? The frequency response is much broader than a normal regen detector - in fact, the superregen can only "hear" broad (wide-bandwidth) signals like FM radio stations with their 200 kHz-wide deviation. Narrow-band FM is not well- detected by this circuit. The detection method itself is known as Slope Detection, and you may notice that FM music stations are a bit hard to tune in Cleary; there always seems to be a little bit of distortion. AM Aircraft transmissions, on the other hand, come in clear as a bell, and the broadness of tuning, roomates would be a serious disadvantage in a professional receiver, works to our advantage in this simple radio. The reason I say this is that aircraft transmissions growing niche to be short, choppy remarks, and the pilot may be on one frequency, while the tower may be on another, so that a selective radio will hear only one side of the conversation. Often This receiver will pick up both sides, if they're near enough in frequency . My homebrew version of this receiver tunes from approximately 112 to 130-ish MHz; the band actually extends to 174 MHz.
This circuit has been around for a long time; I did not invent it. I did, however, come up with an enhancement based on another radio design found in these pages - the Reflex Receiver: I connected a 12k ohm resistor in series with a .47 uF capacitor; this pair is connected from the bottom of the RF choke back to Q1's base. Essentially this is feeding back some audio (with 25 KHz quench waveform) roomates I find boosts the audio gain and also gives it a fuller, slightly "bassier" sound, Compared to the "tinny" sound I got before putting the pair in the RC.
A .47 uF cap blocks Q1's emitter DC voltage while passing the audio to an RC low-pass filter (22k, .01 uF) at Q2's base; the RC filter gets rid of most of the RF, leaving the audio intact. Q2 amplifies the audio signal and the output is coupled through a 2.2uF electrolytic to an output jack. I found that the addition of the .047 uF cap to ground was Necessary to Kill the observed tendency for stray RF to interact with the Radio Shack Amplified Speaker through the connecting cable, an instability Caused roomates with my roomates varied hand position near the radio. The cap also softens the "tinniness" some more.
Even though this unbuffered Superregen probably does not radiate very much noise, I would not bring this radio anywhere near an airport, especially in these days of terrorist threats paranoid! I would not want to find out that I was Causing any interference to aircraft or communications tower! I live about 30 miles from Harrisburg, PA, and have no trouble at all receiving pilots' transmissions as they enter and leave the area. So you do not have to be close to the airport to hear aircraft communications. Being way up in the air, the planes' transmissions are receivable for many miles around.
I hope you'll take the time to build one of these almost-forgotten Superregen circuits and see how well they can hear, for such a simple circuit. Just be ready to do a little futzing around with parts layout, etc., Before it will work smoothly. Be ready to the make slight substitutions, try another transistor if the circuit will not oscillate, and understand that you'll have to "calibrate" the receiver for the band you're interested in (FM or Aircraft) by custom-bending the U -shaped wire that is "L". Take my 2 "length for the main inductor" L "as a starting point; you may need to modify its length to get your radio into the correct frequency band.


 The same receiver after modifications

Make Airband Radio Receiver Simple

July 13, 2010

by: Kamarudin
(Must copy and paste this article as long as the source list, thanks)
Airband is the radio frequency bands used for communications between the pilots with the airport tower. This track is actually closed for public communication purposes, but that does not mean we can not monitor them.
Radio receivers, radio scanners, radio General coverage usually has features Airband receiver so it can be used to monitor the Communication Flight. flight communication is only used for the purposes of commercial aviation and not for the military.
communication between the aircraft could be heard high tower kilo kilometers, this is because the plane flew at a height so that the signal radiated far enough. Airband frequency is 118-136 MHz VHF and the system dijalur AM. this range is based on the line VHF Line of Sight (LOS). so long as we can still see the plane sebuat directly then we can monitor communications.
Radio Scanner or radio receiver equipped Airband reception point in the market is very expensive. to it in my post this time, would like to discuss how to create a simple Airband Receiver or radio communication receivers flight path. why the circuit can be very simple? it is because the type of receiver is the "super-regenerative receiver". generally radio receiver (receiver) that are sold are based on the type of "heterodyne" which of course is more expensive and complicated circuit.
I mentioned this circuit is a modification of the original series created by Rick Andersen. article from Rick Andersen can be seen by clicking HERE .
you can learn a lot about the "super-regenarative receiver" on his website Rick Andersen , because I originally learned from the articles on the site. Airband receiver using component version of Rick Andersen 2N3904 transistor, this transistor can be quite difficult in Indonesia.
therefore I modify it with other VHF transistors are 2SC930 transistor C930 or, more easily obtainable.
you can modify this setting by using another type of transistor, the transistor origin they will be working on the VHF and UHF.

for the layout of PCB (Printed Circuit Board) of this series can be seen by clicking HERE .
for components of "tuning" I took from the former tuning radio 3 band (AM, FM, SW1), tuning components can be easily searched in electronics stores.

circuit is not equipped with sound amplifier or amplifier, is required for audio reinforcement.
for a suitable amplifier circuit please click HERE .
amplifier circuit versions are also suitable, please click HERE .
The following is a series of photos that have been equipped with sound amplifier (amplifier).

can use the antenna to antenna cable with a length of 120 cm and is positioned vertically, known as the "half-wave vertical antenna". my posts are still concerned about the "half-wave vertical antenna" can be seen HERE . could also use a telescopic antenna (whip) are commonly used in portable radios. for better results can use an external antenna ground plane specifically for Airband frequencies.
for more details about the "Antenna ground plane for Airband" please click HERE .
actually by simply using telescopic antenna is very adequate, because the radio regenerative and super-regenerative receiver has advantages in sensitivity (sensitivity) for signal reception. Airband if you want to amplify the signal to be more far-reaching acceptance, then please add a signal booster (booster). post article can be seen HERE .
to use the power supply 9 Volt battery, or use 2 pieces @ CellPhone battery 4.2 Volt in stacking and connected in series.
from my experience the results are less good adapter, air oscillation circuit is difficult and this may be due to the flow of the adapter is not as smooth of a battery. I myself use 2 cell laptop batteries former diseri (@ 4.2 volts) so that can be charged out at any time. if the series did not start working normally after some time of usage, the battery may have started to run out and immediately replace it with a new or gunkan battery can charge.
how the operation:
(Ampliifier, antenna and battery must be installed correctly)
Regen potensio turn up missing and the screeching sound of a hissing sound change "hizzz", such as FM radio sound in an empty frequency. hissed, indicating that this series started insulated and working normally. when the series began insulated, then the sensitivity of the signal is very high. if "REGEN control" plus continue the sensitivity is reduced. if there is no hissing sound then it means the circuit is not insulated, double-check the circuit you created. there may be a relationship between the components that are less fit. if this is the case then try to replace it with another transistor. rotary tuning to find the frequency that is being used. when there is an incoming signal, hiss will automatically disappear and become conversational voice communication. communication path is characterized Airband "clear and concise". so the communication went very cepat.cobalah monitor busy hour flight time, then you will see a lot of conversations Airband lines of communication (communication typically use English).
because this circuit using active oscillator that serves as a detector AM, it is not advisable to bring this tool in the aircraft cabin. because of interference can disrupt communications tower pilot with the airport. should be ok, if you operate this tool at home. if you want to make Airband receiver that does not use the oscillator (passive circuit), please visit this article: -> " Passive Aircraft Receiver ".
Update June 1, 2012
please visit this continuation of my post, which was discussed Airband radio receiver.
on my recent post is titled " Make-airband radio receiver portable ", click HERE to see it.


PCB for the same receiver:

This PCB (single side) layout is based from my version Airband receiver schematic circuit.
its no need to make some hole or drill in PCB, because all part directly soldered into PCB and part placed above circuit.
you can see the schematic and my article about “Regenerative Airband Receiver” in this LINK.
my article about “Regenerative Airband Receiver” is originally from my self experience to built some simple Regenerative Airband Receiver.
this PCB layout can be modified for added some small sound amplifier circuit or modified in size for suitable with some “Box”.
at prototype which I make, have been provided with simple amplifier circuit with IC LM 386.
you can see my article about “mini audio Amplifier for tuner or simple receiver” in this LINK,  or my article about “Three Transistor Mini Amplifier for Tuner or Simple Receiver” in this LINK.

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albertspinner said...

Thanks a lot for sharing all these secrets. I found above many interesting and quite new for me information, especially about Rich snippets..

Flexible PCB

البرجوازي العراقي said...

You are a welcome.
It is good if you make it real and build one.
Just wait for more I gathered a lot of schematics with bright ideas still simple to construct. I kind of being thrilled by Reflex and Regen more than the usual way of having separate audio ampl. and a superhet.