1st IF Amp/2nd Mixer

Reference:    NAVSHIPS 91875(A), para 2g(3)

See figure 2-2 for similarity of circuit connections.  As determined by the mixer output, V551, the first i-f frequency is 1600 kilocycles on all bands.

The first i-f input signal goes to a band pass filter Z902 which passes signal frequencies within a band wide enough for intelligibility, while suppressing extraneous frequency components.  After passing through Z902 the 1600-kilocycle signal is applied to the third grid (pin 4) of V901.  This tube V901 also operates as a 1400-kilocycle crystal-controlled oscillator connected as a Pierce-type circuit, the tube elements involved being the cathode (pin 2), first grid (pin 1) and second grid (pin 7), and the feedback relations being obtained through capacitors C912, C913, and the interelectrode capacitance of the tube elements.  The 1400-kc signal thus produced and the 1600-kc signal applied to the grid (pin 4) combine to produce a 200-kc signal in the plate (pin 5) circuit of V901 which is then fed through S902 to the primary tuned circuit T901. The signal from the secondary of T901 goes through J902B to the second i-f input J1001B.

Josh Rovero,
Aug 3, 2011, 6:18 PM