In this circuit, the 40‑meter antenna signal enters through the base of the RF transistor, while the VFO signal is applied at the emitter. Both signals mix at that transistor stage, and the resulting product includes the desired 10.7 MHz IF, which is then passed into the receiver’s IF strip.

This configuration lets the radio receive AM signals on 40 m using its original 10.7 MHz → 455 kHz → detector chain.

For SSB reception, you must add a BFO. Inject a small carrier signal (around 451–455 kHz) into the emitter of one of the last two IF transistors before the detector. This re‑inserts the missing carrier so the 455 kHz IF can be demodulated as USB/LSB.