Reference: NAVSHIPS 91875(A), para 2n
The crystal calibrator circuit provides accurate frequency check points for calibrating the main tuning dial. These check points occur at every 10 kc throughout the tuning range of the AN/SRR-11 receiver, at every 50 kilocycles of the AN/SRR-12, and every 200 kilocycles of the AN/SRR-13. The calibrator circuits are described separately for the three receiver types.
(3) 200-KC CRYSTAL CALIBRATOR (AN/SRR-13).-- Refer to figure 2-7. The crystal calibrator circuit used in the AN/SRR-13 receiver is a cathode coupled multivibrator, V1201 and V1202, which is locked to 200 kilocycles by Y1201. Resistor R1206 is a parasitic suppressor and capacitor C1208 aids the grid-to-plate capacity of V1201 to increase its feedback. One output, rich in harmonics of 200 kc, is taken from the plate of V1202 and applied to the grid pin 1 of the r-f amplifier V526 through C1205, J1201-C, J501-M, C502, J501-L, J526-B, S526-A. After passing through V526, the signal is combined in the mixer V551 with the signal from the local oscillator V601. The combination-frequency signal output of V551 then goes through switches S1001, S1002 and associated networks through V1001, to the input circuit of V1002. In this last circuit, it combines with a second output from V1201/V1202.
The second output is taken from the common cathodes of V1201 and V1202, and its fourth harmonic is applied to V1002 of the second i-f assembly as just mentioned. The combination of the two signals gives a beat note at every 200-kilocycle interval throughout the tuning range of the receiver. The main tuning dial can thereby be calibrated independently of external signals if the CAL switch is turned to the ON position.
The CAL switch, S562, is connected so that in the OFF position B+ voltage is not applied to the crystal calibrator. In the ON position, B+ voltage is applied to the calibrator, and is removed from the antenna preamplifier, V501, and BFO, V1301. This prevents interference with the crystal calibrator from either externally applied signals or the BFO.