TM  1-1520-240-10 3-2-12            c.  Frequency Range. The frequency range is 30 to 87.975 MHz channelized in tuning increments of 25 kHz. In addition a frequency offset tuning capability of -10 kHz, -5kHz, +1kHz is provided in both receive and transmit mode; this frequency is not used in the ECCM mode. d.  Homing. (1) Mode select switch — HOM. (2) Operating frequency — Set. NOTE Any strong single channel signal within the frequency range of the radio set can be used for homing. (3) FM button on HSI MODE SELECT PANEL — press. Check that SEL lamp is lit. (4) Homing procedures. The course deviation bar on the HSI provides the primary navigation indication when the set is in homing mode. The bar only provides information  on  whether  the  helicopter  is  left,  right,  on heading to a signal source, or over the signal source. The TO-FROM ambiguity arrows will not function and selec- tive source feature is not available. Ambiguity is solved using either of the following methods: (a) Directional method. When the helicop- ter is heading inbound to the signal source with the bar centered, the indications are directional in that a change in heading to the right will cause the bar to drift to the left. Conversely, a change in heading to the left will cause the bar to drift to the right. When the helicopter is heading outbound from the signal source with the vertical pointer centered, the indications are nondirectional in terms of steering. A change in heading to the right will cause the bar to drift to the right. A change in heading to the left will cause the bar to drift to the left. (b) Build  and  fade  method.  If  the  signal source is transmitting a 150-Hz tone-modulated signal and the helicopter is inbound to the signal source, the tone will increase in intensity. The tone will decrease in intensity on an outbound heading. (5) Additional homing characteristics. The fol- lowing additional characteristics may be observed when homing. The glideslope deviation pointer will rise from the horizontal mark when the aircraft is inbound (increas- ing signal strength) to a transmitter. The pointer will fall to the horizontal mark when outbound. The glidescope failure and navigation failure warning flags will be in view if there is inadequate homing signal strength. A dip in the horizontal pointer may or may not occur when passing over the station, depending on the signal source, helicop- ter speed, and altitude. 3-2-17.  Controls    and    Functions    VHF/FM    Radio Set.  (fig.3-2-6) CONTROLS/ INDICATOR FUNCTION Function Selector OFF Primary power OFF. Memory battery power ON. TEST RT and ECCM modules are tested. Results; GOOD or FAIL. SQ ON RT on with squelch. SQ OFF RT with no squelch. RXMT RT in RECEIVE mode. Used as a radio relay link. LD Keyboard loading of preset fre- quencies. LD-V TRANSEC variable loading is enabled. Z-A Not an operational position. Used to clear the TRANSEC variable. STOW All power removed. Used dur- ing extended storage. Mode Selector HOM Homing antennas are active; communication antenna is dis- connected. Provides pilot steering, station approach, and signal strength indicators. SC Single channel mode of opera- tion. Operating frequency se- lected by PRESET selector keyboard entry. FH Frequency hopping mode se- lected. PRESET selector posi- tions 1-6 select frequency hop- ping net parameters. FM-M Frequency hopping-master position selects control station as the time standard for com- municating equipment. Preset Selector MAN Used in a single mode to se- lect any operating frequency in 25 kHz increments.