Understanding this 8Mhz on-off keyed reception circuit
Enable Rx has 2 cascaded inverting (Q6/Q4) NPN's so Hi input gives open circuit high output, not low and also Q1 NPN/PNP to enable power for U7

C33 shunts the RF on one side to make it a single ended input.

C31,32 makes a tank circuit and impedance/voltage divider ratio to keep the input impedance of the SA612 from lowering the Q of the tank circuit.

The RFin =1.5k of the SA612.

470pF is around 50 ohms so the Q is around 30.

To get 128kHz, the mixer clk has to be 128kHz higher (or lower) than the 8MHz RF input or 8.128MHz