Reference: NAVSHIPS 91875(A), para 2h(3)
In the AN/SRR-11 the TUNING meter M251 is connected to indicate the current in the diode detector, V1005. In the AN/SRR-12 and AN/SRR-13 the output of the third amplifier, V1003, is applied to a 200-kilocycle tuned circuit in Z1009 and rectified by a crystal rectifier CR1001 to actuate the movement of the TUNING meter M451 or M651 mounted on the front panel. When the desired signal is detuned, the rectified signal voltage applied to the TUNING meter is low, and the meter reads down scale. As the desired signal is tuned, the rectified voltage increases and the TUNING meter reads up scale. The HIGH-LOW switch, S254, S454, S654 (depending on the receiver type) mounted below the TUNING meter on the front panel, attenuates the meter reading when the switch is in the LOW position by connecting a shunt resistor R253, across the meter for AN/SRR-11 or adding a series resistor R453 or R653 for the AN/SRR-12 and -13. This resistor is removed when the switch is in the HIGH position.