I built this superregenerative FM broadcast band receiver today.
Here is a list of parts values I used:
ANT – 12 cm insulated wire connected through 10 pF capacitor to FET source.
C4 – two 2.2 nF MLCCs from + to ground plane ( I built this on a small piece of copper circuit board.)
C5 – 18 pF silver mica capacitor
C6 – not used – shorted.
C7 (A and B) – two 0.2 to 5 pF plastic variable capacitors
C3 – 10 pF silver mica capacitor
R3 – 2.7 M 5% carbon film resistor
R4 – 22k 5% carbon film resistor
Q1 – 2N3819 VHF JFET
Q2 – C9018 high gain low noise NPN BJT
L1 – 6 turns 20 AWG bare copper wire wound on drill bit shank, appx 6mm ID. Coil stretched so it measured appx 120 nH.
L2 – 6 turns 24 AWG solid insulated wire on a FT37-43 toroid core, measured 14 uH
(Following copied from FB post)
My Superregen won’t quench. I built the circuit found here, with a few changes.
I used a 2N3819 for Q1, and a FT37-43 for L2, measuring 14 uH. At the end in his notes he gave some limits to the values of some parts, and the values I used seem to be within the limits.
For an antenna I connected a short 12 cm length of wire to the FET’s source, as he recommended. The coil is 6 turns of 20 AWG bare copper wire, wound on a drill bit shank, and spread out untl it measured about 120 nanohenrys. I used an 18 pF silver mica capacitor and two 0.2 to 5 pF variable capacitors in parallel with the coil.
I used a dip meter to tune the coil and capacitors to a point within the FM broadcast band. I measure a little over 2 volts at the source, so the JFET is conducting in the linear region.
I used a scope to check the R1 – C1 point and I see no oscillations. I’m using 9VDC regulated for the supply. I connected the Q2 output to an amplifier and I get noise like a hiss but no stations. I can hear my cell phone burps loudly, and hum if I touch points in the circuit. So I’m fairly confident that I have the circuit set up properly – no major malfunctions.
I just thought of one thing I can do. I can put the circuit on a variable supply and try various supply voltages. I’ll try that and update this.
Update evening until 1:30 AM – I experimented with several different parts. I put it on a variable supply and it seemed to do a little bit better at 6 volts. At the beginning of this session I could receive only a single FM station, one that’s very close and powerful. This was with the 12 cm wire connected through a 10 pF capacitor to the source. I couldn’t hear any other stations.
I removed the L2 and rewound it, so it has 9 turns on the FT37-43 core and measured 33 uH. The audio seemed to be louder. But as I tune, the audio is garbled, seems that the level is too high for the audio amplifier I’m using. Still only one station.
I moved ‘center tap’ one turn closer to the positive end of the tank coil. I also spread the turns a bit, and adjusted the variable capacitors a lot. I think the coil could be longer and lower inductance so it will cover the high end of the FM band.