Super Regen: Make it work

@8/23/1012

i always want to discuss this topic for my 27Mhz: Walkie Talkie Experiment  but there is not enough experience or things  to talk about. i did built SuperRegen: AirCraft band receiver  one year ago, and built it again and again these days,  this teach me something.

This the  27Mhz receiver for experimental walkie talkie.  the problem is this receiver is far away to achieve sensitivity. i didn't know why , a month ago.

I capture the waveform use Oscilloscope

The quench waveform seems not good.  We will talk about this receiver later.

this project make me learn much about super regenerative receiver.

after connect every component correctly, the next task is check the RF oscillation and then the quench. 

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 are dead points, try increase C1, or add C13 to BE junction.  most super-regenerative receiver use 2N2222, 2N3906 transistor, which Ft around 100Mhz to 300Mhz. but, if you use 2SC9018 or other type transistor,  especially high Ft, 1G or even more,   this oscillator often can not start oscillating in the low end of tune range, I try to figure out the reason moths ago in another project,  refer to  VFO: ultra-audion LF to VHF , the solution is just increase C1 or  add C13.

2. the filter circuit for audio output

for a adjustable quench, POT P1 was solded.  At first, i use 5K POT with 0.001uF capacitor and check it by oscilloscope, the RF and quench is work well. but  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 hearable  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 an option worthy to try,  refer to : 27Mhz: Walkie Talkie Experiment

3. Performance: Quench frequency and bias

now i hear a little bit hiss noise. but the receiver is not sensitive,  i suspect the quench frequency is not right,  by soldering a 47k POT,  i find  22k resistor could  make it most sensitive. at same time the bias also changed, i do not know what happens exactly at that time.

the following experiment show if we  change only the quench frequency,  there is no performance change at all.  this indicating the bias is the key to a good super-regenerative receiver like Regenerative, if we get the detector just begin oscillating, we get the most sensitivity.[fix me]

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

detect the AM and the FM need different bias setting to get best voice, enjoy that!

1.  check whether the oscillator is work

2.  check whether the quench work, and  frequency is acceptable

3.  check whether the quench signal is filtered out from audio signal

4.  change the bias to get best performance