What circuit combines signals from an IF amplifier stage and a beat-frequency oscillator (BFO), to produce an audio signal?

A product detector is a specialized mixer circuit used in receivers to demodulate Single Sideband (SSB) and Continuous Wave (CW) signals. It takes the intermediate frequency (IF) signal and mixes it with an unmodulated signal from the beat-frequency oscillator (BFO). By multiplying (taking the "product" of) these two signals, the circuit creates sum and difference frequencies. The difference frequency falls directly into the baseband audio range, allowing you to hear the transmitted voice or CW tone. The other options serve entirely different functions. A Variable Frequency Oscillator (VFO) is used to tune the radio's operating frequency, an Automatic Gain Control (AGC) circuit regulates audio levels to prevent blasting, and a power supply distributes voltage to the components.