TM  1-1520-240-10 3-2-10            NOTE The antenna select system has no effect on the FM homing antenna. The homing antenna (towel bar) is on the bottom of the fuselage aft of the cockpit (fig. 3-2-3) and is connected to the FM set only. 3-2-14.  Controls  and  Function,  VHF  AM/FM  Radio Set.   (fig. 3-2-5) CONTROLS/ INDICATOR FUNCTION Mode Select Switch Three position rotary switch used to select radio operating mode. Power is applied to ra- dio in all positions except OFF. OFF Power to set is disabled, radio is inoperative. TR Radio operates in the transmit- receive mode. DF Radio operates in the direction finder mode. Frequency Control/ Emergency Select Switch Four position rotary used to select radio frequency tuning mode. EMER AM Radio is tuned to AM Guard channel frequency. EMER FM Radio is tuned to FM Guard channel frequency. MAN Allows manual tuning of radio operating frequency. PRE Allows selection of any 20 pre- set operating frequencies. VOL Rotary control adjusts radio output volume. SQ DIS/TONE Switch Three position toggle switch used to select radio squelch operations. Normal (center position) Preset squelch level is se- lected. SQ DIS Squelch operation is disabled. TONE Not used - maintenance opera- tion only. Preset Channel Se- lector Twenty position rotary control used to select any 20 preset channel frequencies. CHAN Display selected radio operat- ing preset channel. CONTROLS/ INDICATOR FUNCTION Frequency Controls Four rotary controls used to manually select radio operat- ing frequency. 10 MHz Control Thirteen position (03 through 17) rotary control used to se- lect first and second digits of operating frequency. 1 MHz Control Ten position (0 through 9) rotary control used to select third digit of operating frequen- cy. 0.1 MHz Control Ten position (0 through 9) rotary control used to select fourth digit of operating fre- quency 0.025 MHz Control Four position rotary control used to select fifth and sixth digits (00 through 75) of oper- ating frequency in 0.025 MHz increments. Frequency Display Display selected radio operat- ing frequency. WB/NB/MEM LOAD Switch (under chan- nel card) Three position toggle switch used to select radio operating band, and during preset chan- nel frequency loading. NB Places radio in NB (narrow band) operation. WB Places radio in WB (wide band) operation. NOTE Switch  will  remain  in  WB  position  unless otherwise instructed by radio set controller. MEM LOAD Momentary contact position used with frequency controls and channel selector to load preset channels. 3-2-15.  Normal Operation – AM/FM Radio Set. The following steps provide operating procedures. a.  Starting. (1) Interphone control panel -— Set switches as follows: (a) Receiver 3 switch — ON (b) Selector switch — 3. (2) VHF ANT SEL switch — SYS 2 – SYS 1.