TM  1-1520-240-10            3-3-3 CONTROLS/ INDICATOR FUNCTION AUDIO Control Adjusts audio level in COMP position. Used as RF gain control in LOOP or ANT position. LOOP Switch When function switch is set to LOOP, LOOP switch enables manual rotation of ADF loop an- tenna and bearing indi- cator pointer left or right for manual direction finding, or when homing to a radio station. Re- turning LOOP switch to center position stops rotation of bearing indi- cator pointer at any de- sired position. Figure  3-3-2.  Direction Finder Control CONTROLS/ INDICATOR FUNCTION Coarse Tune Control Tunes receiver in 100 kHz steps as indicated by first two digits of KI- LOHERTZ indicator. Fine Tune Control Provides selection of 10 kHz digits (continuous tuning) as indicated by last two digits of KI- LOHERTZ indicator. CONTROLS/ INDICATOR FUNCTION KILOHERTZ Indicator Displays operating fre- quency to which receiv- er is tuned. TUNE Meter Provides indication of relative signal strength while tuning receiver to specific radio signal. CW-VOICE-TEST Switch Three position toggle switch. Spring-loaded from TEST. CW Enables the beat fre- quency oscillator (BFO) to permit tuning to con- tinuous wave stations. VOICE Enables the set to oper- ate as an AM receiver. TEST Rotates the bearing indi- cator approximately 180_ to check operation of the set. The TEST switch functions when the function switch is at COMP only. 3-3-7.  Normal Operation — Direction Finder Set.  The following paragraphs discuss ADF set opera- tion. a.  Starting. (1) Interphone control panel - Receivers NAV switch — ON. (2) Mode switch — ON. (3) CW-VOICE-TEST — CW or VOICE. (4) Tune  controls  —  Set  frequency.  Tune  for maximum signal strength on the tuning meter. (5) AUDIO control — Adjust. b.  ADF Operation. (1) VOR ADF switch on HSI MODE SELECT panel — Press, if ADF segment is not lit. (2) Check for the correct bearing indication, on HSI No. 2 bearing pointer. c.  Radio Receiver Operation. (1) Function switch — ANT (2) Tune control — Set frequency; then tune for maximum signal strength on the tuning meter. d.  Aural Null. (1) CW-VOICE-TEST switch — CW. (2) Function switch — LOOP. (3) Loop switch — Rotate for audio and tune indicator null. Release switch. Observe bearing to station on  indicators.  Two  null  positions,  180_  apart,  may  be obtained.