Regenerative RX

Regenerative receiver schematic

This simple design is based on a 'Regenerative' tuned radio freqeuncy-type receiver. The antenna signal enters RF amplifier Q1 and coupled via LI. This induces a small signal into winding L2 which is brought to resonant frequency by the 365pF variable capacitor.
The signal is then rectified and amplified by FET Q2. A small portion of this signal is taken from the Drain of Q2 and fed back to the signal input via L3. In thoery this greatly increase the 'Q' of the circuit and also the selectivity. The 60pF variable capacitor adjusts the amount of feedback in the circuit. The supply for this part of the circuit is taken via the 6V8 zener diode for better stability.

After Q2 the rectified Af signal is amplified by IC1 - a small audio power amplifier which is sufficient to drive a small loudspeaker or headphones. Switch S1 connects the 22nF capacitor across the audio input and is just a very simple low-pass filter.

Using the set:
Connect an antenna and 9v - 12v DC supply. Adjust the feedback capacitor for minimum capacitance and the AF control to approx. mid travel.
When you find a signal adjust the feedback until just before the point of oscillation. Too much feedback will result in howling and other unwanted noise on the output. Too litle and the receiver will appear to be dead. When set correctly the sensitivity and selectivity will greatly improve the performance of the receiver.

When receiving broadcast or SSB signals it's best to have 22nF capacitor (S1) out of circuit. Try this in circuit when resolving CW signals.

For more details of wire thicknesses, see Wire Guages on the Index page.

Scrolling line

Best Regards... Pete

http://www.keirle.fsnet.co.uk