TM  1-1520-240-10 3-2-18            3-2-24.  Operating  Modes/Functions,  HF  Radio  Set (AN/ARC-220).   (fig. 3-2-8) CONTROLS/ INDICATOR FUNCTION Power ON/OFF On function Switch. CRT Brightness Two pushbuttons switches used to vary brightness. The (up arrow) increases inten- sity while the (down arrow) decreases intensity. System Turn-On Turning the Function Switch clock-wise from OFF to STBY turns system on and selects standby function. SYSTEM TESTING is dis- played while power-up BIT (P-BIT) is in process. SYS- TEM -GO will be displayed if all tests good, SYSTEM- NOGO if not. Audio Volume Eight-position rotary switch varies output level. Setting is displayed on line 6 (bottom) of display for 5 seconds when system first turned on or when VOL setting is chan- ged. The display level are 1, 2, 3 thru 8. Channel Selection Channel number may be changed using the Channel Selector seven-position rotary switch. The + position of the greater to be selected using the VALUE switch. Modulation Mode Four modes are available: USB, LSB, AME, and CW. To change modes, depress the EDIT line select switch. While in the Edit screen use the CURSOR switches to position cursor under the ap- propriate emission mode (RCV or XMT). Use the VAL- UE switches to change mode. (Note: The XMT mode will automatically change with RCV mode, but the reverse is not true). Depress RTN line select switch to enter the edited data and return to op- erational mode. CONTROLS/ INDICATOR FUNCTION Receive/Transmit Frequency 2.0 - 29.9999 MHz, program- mable in 100 HZ steps. To change frequencies, depress the EDIT line select switch. While in the Edit screen use the Cursor switches to posi- tion cursor under the ap- propriate frequency. Use the VALUE switches to change frequency. (Note: The XMT frequency will automatically change with the RCV fre- quency, but the reverse is not true). Squelch Level/ Audio Muting Two pushbutton switches -SQL +, when pressed dis- plays the squelch status on line 6 of display for 5 se- conds. Settings are TONE and 0 through 5. TONE pro- vides no muting and no squelch. Position 0 provides muting but no squelch. Posi- tions 1 through 5 provide muting and increasing levels of squelch. Muting is normal- ly enabled during ALE and ALE ECCM operation. Output Power Level Three output levels are se- lectable for the display screen by using the EDIT line-select switch, which brings up the edit mode, moving the cursor under the power character field and us- ing the VALUE switches to change the field. Depress the RTN line-select switch which stores the change and re- turns to normal operating mode. There are two Built-in- Test (BIT) features which concerns the operator, P-BIT and C-BIT. The Power-UP Bit (P-BIT) test the ARC-220 when initially turned on. P-Bit exercise basic radio control functions which must be op- erational prior to entering a system operational mode. A GO/NO/-GO status appears on the display and defaults to standby mode upon comple- tion. When NO-GO status ap- pears, depressing the