TM  1-1520-240-10 3-2-16            3-2-21.  HF Radio Set (AN/ARC-220). WARNING ANTENNA DANGERS The HF Radio Liaison Facility AN/ARC-220 in the ALE mode sounds (transmits short tone bursts) and replies to ALE calls auto- matically without operator action. Anytime local flight directives forbid HF emissions, such as during ordinance loading and re- fueling,  or  when  personnel  are  working near the aircraft, ensure the radio set con- trol function switch is set to SILENT, STBY, or OFF. The HF radio set (AN/ARC-220) provides communica- tions in a 28 MHz high frequency band between 2.0 and 29.9999  MHz.  Channels  are  spaced  at  100-Hz  incre- ments, giving 280,00 possible frequencies. Preset chan- nels can be manually programmed or preprogrammed as part of the communications mission load information. A total of 72 channels can be programmed: 20 manual simplex or half-duplex, 20 programmable simplex or half- duplex,  20  programmable  ALE  scan  lists  and  12  pro- grammable ECCM hop-sets (with ALE capability). Oper- ating modes of the HF radio set using either simplex or half-duplex  operation  are  Upper  and  Lower  sideband (USB,  LSB),  amplitude  modulation  equivalent  (AME), and continuous wave (CW). Data may be transmitted or received in USB or LSB modes. Both standard and ad- vanced narrow-band digital voice terminal (ANDVT) are supported. DC power to operate the HF radio set is sup- plied by the No. 2 DC bus through the COMM ARC-220 HF circuit breaker on the No. 2 PDP. 3-2-22.  Controls  and  Function,  HF  Radio  Set  (AN/ ARC-220).   (fig. 3-2-8) CONTROLS/ INDICATOR FUNCTION Cursor (1) Four pushbutton switches position the cursor verticallyor horizontally. Line-Select (3) Pushbutton switches to select options displayed to left of each switch. Brightness (4) Pushbutton switches to vary display brightness. Channel/Net Selec- tor (5) Seven-position rotary switch used to select programmed operating channels or nets. CONTROLS/ INDICATOR FUNCTION Data Connector (6) Interfaces ARC-220 system to data transfer device for datafill. Key Connector (7) Interfaces ARC-220 system to data transfer device for keyfill. Mode Switch (8) Five position rotary switch se- lects mode of operation. MAN Selects HF conventional com- munications. Operating fre- quency and emission mode are selected manually. Se- lected information can be stored in preset channels for future recall. PRE Selects conventional HF com- munications. Channel/net se- lector is used to select prepro- grammed preset channel. Fre- quency and emission mode cannot be changed during pre- set operation. ALE Selects automatic link estab- lishment mode of operation. ECCM Selects electronic counter- countermeasure mode of op- eration. EMER Used during emergency to place a distress call. The mode, frequency, net, etc., is determined by the datafill. SQL (9) Two pushbutton switches which controls squelch and au- dio muting. VOL (10) Eight-position rotary switch varies the receive audio output level. Function Switch (11) Five-position rotary switch se- lects system operation func- tion. OFF Turns the ARC-220 off. STBY Selects the standby function where built-in test (BIT), setup, or fill operations can be per- formed. SILENT Used in ALE or ALE ECCM modes to prevent the ARC-220 from automatically responding to incoming calls.