Reference: NAVSHIPS 91875(A), para 2h(4)
Output from the third i-f amplifier, V1003, is fed to the first grid of the BFO-mixer, pin 1 of V1004. Signals from the beat frequency oscillator V1301 are applied to the third grid, pin 4, of V1004 through capacitor C1306. The 200-kilocycle i-f signal and the signal from the BFO are heterodyned in V1004 to produce a difference frequency in the audio range. This difference frequency component is fed to the audio amplifier V1102 through S1003, J1002N, J110D, and S1101A, when the RECEPTION control is set at A1 BROAD, A1 SHARP (and A1 MEDIUM for AN/SRR-13A). When this control is set at FSK, the signal goes through V1102 through S1003, J1002N, the center arm of the OUTPUT control R257B, R457B, or R657B (depending on receiver type), J1101J, and S1101A.