SuperRegen: AirCraft band receiver

2012/8/20

let me show the image first, built done @2012/9

Two years ago,  I built  a KE3iJ's air craft super regenerative receiver.

For detail information please refer to:  http://www.ke3ij.com/superrgn.htm

In this version my antenna use 1.2 meter folded to 60cm, Q1 use 2SC9018.  Q2 use 9014. I even built it on breadboard, that just work by utilized the parasitic capacitance, but, that's might can not be reproduced.

Rebuilt again and again till today

 2 years later I'm going to make a permanent version. it will be in a box  finally. I build  3 of them in a week to find why it's hard to make it work and repeatable. here is the final schematic,  different transistor different coils.

I revised it a little bit . using different transistor to ke3ij.

1. add C13 to detector's BE junction  for easy start oscillation, the reason refer to  my VFO: ultra-audion LF to VHF

2. add C14  to minimized super-regen/reflex noise.

3. add noise NFB C2  to audio pre-amplifier for prevent oscillation when connect to a high gain audio power amplifier. 

4. R7/R3 added for decouple, this will prevent audio "motor boating" oscillation. then audio signal can extract from R7 also.

5. P1 to fine tune the quench, and the bias.  P2 for only adjustable bias .

Important note:

The C8 is very important to filter out quench oscillation, otherwise you don not  hear anything....

the Audio amplifier

You'd ensure you connect every component correctly, and if it still receive nothing. here is step to debug. I built it again and again i learn 2 things to make it work, the RF  and the quench . the super regenerative receive is a combination of  2 oscillators, the RF and the quench. while RF and quench is ready, the receiver is done.

1.  Make RF oscillator work

you can check is the RF work by check the sawtooth of the quench. once  you get saw tooth at top of P1, indicate the receiver is ready to receive signal.

in case it not oscillate, or there is dead point, try increase C1, or add C13 to BE junction. this ensure in a reasonable tune range without  "dead spots" and "flutter" point.

if you change T1, from 9018 to other type transistor especially high Ft, it often can not start oscillating in the low end of tune range, the reason, check my another experiment: VFO: ultra-audion LF to VHF , the solution is just increase C1 or  add C13.

2. the filter circuit for audio output

when i built the 3rd version,  i try to make quench adjustable. use P1.  At first, i use 5K POT with 0.001uF capacitor. i check it by oscilloscope.  i ensure RF and quench is work well. but you know what,  it can not receive anything, even no hiss noise.

i check the circuit use oscilloscope,   find the sawtooth quench signal is delivered  by T2 instead of the audio,  that's is not hear-able  signal. carefully check found i dos not solder the C8[T2's collector],  C8 is the key to filter out the quench signal. a collector audio output is a option worthy to try,  refer to : 27Mhz: Walkie Talkie Experiment

3. Performance: Quench frequncy and bias

now i hear a little bit hiss noise. but lightly, the receiver is not sensitive,  i doubt the quench frequncy,  then, a 47k POT is soldered,  finally a 22k resistor make the most sensitive receiver. but the bias changed also, i do not know what happens exactly.  [continue this topic in Super Regen: Make it work.] 

the next experimental show if just change the quench frequncy,  there is no performance change.  this show the bias is the key to a good super-regenerative receiver.  this is reasonable, like Regenerative, just oscillating, the most sensitive.[fix me]

Another important thing about self quench is that: while tuning a widely range, i.e from top of 100Mhz to around 150Mhz. the quench frequency is changed along with RF. from around 100Mhz to 150Mhz, quench frequency from 270khz to 300khz.

finally detect the AM and the FM need different bias setting to get clear voice, enjoy!

4. decouple: highly recommended put a resistor to collector of  detector transistor T1, form a decouple network, the value from 1k to 10k. use POT to determined the best value.

there is a way to temporarily  improve the signal strength: connect random wire to GND, near the detector transistor.  connect it when you try to receive something at the first time.  this way make easy to find signal. but some time this lead to "motor boating" oscillation.

and there is a amazing phenomenon, after boxing, it's performance much better than it's out of box, might because:

1) use double side PCB as ground

2) short wire connection

and there is no body effect at all!  voice clear and loud for AM of aircraft. 

Final thought

When change a design, use POT to make adjust easy. the receiver performance is good.   Air Band use super receiver is almost a nightmare. the most time there is no signal, or it's weak,  the loudly noise make you crazy. listen to AM/FM broadcast is acceptable anyway.