SSB Demodulator Circuit

Demodulating mixers are used to to demodulate single-sideband (SSB) signals. The circuit diagram of balanced SSB demodulator is shown in Figure 1. It has an advantage it almost doesn't detect AM signals, therefore it reduces AM interference to SSB reception at the receiver output. Moreover, this balanced demodulator has improved selectivity.

SSB Demodulator Circuit

Fig. 1.
Balanced SSB demodulator

C1 - 180pF, C2 - 300pF;
C3, C4 - 5.5pF, C5 - 2nF, C6 - 0.02μF;
R1, R2 - 10k, R3 - 10k (trimming potentiometer);
D1, D2 - D2J (1N41);
L1, L2 - see the text.

Any standard intermediate frequency (IF) coils can be used for L1, L2, but it takes to change the second winding of L2. Wound it with two wires in parallel, then connect the end of one wire to the beginning of the other wire, and connect this node to the ground. L2 having 0.4T+0.4T turns of original wounding, where T - the original number of turns.

To adjust the demodulator, tune the L1L2 resonant tank to get maximum volume of reception, match the local oscillator voltage to get best reception. Turn off the local oscillator, then balance the demodulator using potentiometer R3 to minimize the audio signal. Turn local oscillator on, and if the audio volume increases sharply, it means that the demodulator is properly balanced.

I. Shkultetskiy (UC2WQ), Polotsk.
"Radio" magazine, November 1964.