Figure 3-4. VHF Communications Transceiver Control Unit

TM 1-1510-223-10 Figure 3-4. VHF Communications Transceiver Control Unit the channel numbers without changing the preset display. Push the STO switch a second time to commit the preset frequency to memory in the selected location. After approximately 5 seconds, the control will return to normal operation. (4) Tuning knobs. Two concentric tuning knobs control the preset or active frequency displays. The larger knob changes the three digits to the left of the decimal point in 1-MHz steps. The smaller knob changes the two digits to the right of the decimal point in 50-IkH steps (or in 25-kHz steps for the first two steps after the direction of rotation has been reversed). The numbers will roll over at the upper and lower frequency limits. (5) Active switch. The active switch, placarded ACT, enables the tuning knobs to directly tune the VHF transceiver, when depressed and held for two seconds. The bottom window will display dashes and the upper window will continue to display the active frequency. Pushing the ACT switch a second time will return the control unit to the normal two-display mode. (6) Test switch. This switch placarded TEST initiates the transceiver self-test diagnostic routine. (Self-test is active only when the TEST switch is pressed.) (7) Light sensor. This built-in light sensor automatically controls display brightness. (8) Volume control. The volume control is con- centric with the power and mode switch (9) Power and mode switch. The power and mode switch contains three detented positions. The ON and OFF positions switch system power. The SQ OFF position disables the receiver squelch circuits. (10) Annunciators. The transceiver control unit contains a MEM (memory) and a TX (transmit) annunciator. The MEM annunciator illuminates whenever a preset frequency is being displayed in the lower window. The TX annunciator illuminates whenever the transceiver is transmitting. (11) Preset frequency display. Displays the pre- set (inactive) frequency and diagnostic messages. (12) Compare annunciator. An annunciator placarded ACT momentarily illuminates when frequencies are being changed. The ACT annunciator flashes if the actual radio frequency to which the transceiver is tuned is not identical to the frequency shown in the active frequency display. c. Operating Procedures. The frequencies displayed on the transceiver control unit show only five of the six digits. The sixth digit is always a zero (when the fifth digit 3-8