HF LIAISON FACILITY OPERATIONAL CHECK (CONTINUED)

TM 55-1520-240-T 18-4.3 HF LIAISON FACILITY OPERATIONAL CHECK (CONTINUED) 18-4.3 TASK RESULT 12. Turn HF Control (4) Function Switch (7) to T/R, Mode Switch (11) to MAN, Channel/Net Selector (14) to 1, and press the Edit line- select switch (3). Using the cursor keys (23), move cursor to beginning of RCV field and use the Value switches (12) to enter frequency of 2.5 MHz, AM mode. Press RTN line-select switch (3). 13. While still tuned to 2.5MHz, AM, set SQUELCH to minimum by depressing SQL pushbuttons (16). Adjust VOL control (15) to a comfortable listening level. Note pitch of audio tone received. Then change to USB then to LSB mode. Also, vary squelch setting by depressing SQL pushbuttons (16) to verify audio can be muted and unmuted. This tests reception of a distant station which broadcasts time and frequency primary standards. If reception is not clear, go to task 18-4.10. If the pitch of the audio tone received changes significantly, go to next task. If squelch does not vary while depressing SQL pushbuttons (16) or audio cannot be muted or unmuted, replace HF Control C-12436/URC. 14. Repeat steps 12 and 13 for the following frequencies: 3.334, 5.0, 7.335, 10.0, 15.0 and 20.0 MHz. 15. Using either a preset or manually entered authorized test frequency establish communications with a known properly functioning ground station (NOTE: If ground station is on the same field, set the output power to LOW so communications will not be distorted). NOTE Ensure Keys and Data are loaded into ARC-220 (steps 10 and 11) before performing step 16. 16. Set HF Control (4) Function Switch (7) to T/R, and Mode Switch (11) to ALE. Establish communication with a known properly functioning ground station with a compatible ALE fill. Set Channel/Net selector (14) of aircraft radio to call address of ground station. Place a call from aircraft HF radio to ground station. After a link Is established and a call made to the ground station, allow the link to be broken by not using the radio for a period of time (normally around 30 seconds, but the exact time Is programmed in the fill). Set the Channel/Net selector of ground station to called address of the aircraft radio under test and place a call to aircraft radio. Results should be the same as steps 12 and 13. Ensure selected channel is heard loud and clear without undesirable chirps, squeals, or hums, thru both aircraft and ground station radios. If not refer to task 18-4.10. The radio the call is being generated from should display CALLING on HF Control Display line 3. After an appropriate delay a short gong tone is heard in the headset and LINKED is displayed on display line 3. If CALL FAIL is displayed on display line 3, go to task 18-4.11. Communication can begin after link is established. Headset audio is muted until a link is established. If headset audio is not muted or communications cannot be established or is not clear, go to task 18-4.10. After a period of inactivity the link should be broken. If link does not break, replace HF Receiver-Transmitter RT-1749/URC. The radio receiving an ALE call, will have INCOMING CALL displayed on HF Control display line 3 and the address fields will change to the caller’s. TASK RESULT ALE address. When a link is established, a short gong tone is heard in the headset and LINKED is displayed on display line 3. Communication should then be generated by the calling station. If reception is not clear, go to task 18-4.10. NOTE Ensure Keys and Data are loaded into ARC-220 (steps 10 and 11) before performing step 17. 17. Set HF Control (4) Function Switch (7) to T/R, and Mode Switch (7) to ECCM. Establish communication with a known functional ground station with a compatible ECCM fill. Set Channel/Net selector (14) of aircraft radio to ECCM net of ground station. Place a call from aircraft HF radio to ground station. After a link is established and a call made to the ground station, allow the link to be broken by not using the radio for a period of time (normally around 30 seconds, the exact time is programmed in the fill). Set the Channel/Net selector of ground station to ECCM net of the aircraft radio under test and place a call to aircraft radio. NOTE Perform the following step after all checks are complete and just before shutdown. 18. Gently pull and turn HF Control (4) Function Switch (7) to ZERO position. If the HF Control displays UNTUNED or UNSYNCH after an ECCM net is chosen, either press TUNE line-select switch or microphone PTT switch. HF Control (4) will display TUNING followed by SYNCHING while the process is occurring. When SYNCHING is no longer displayed, the system is ready for ECCM operation. If system cannot be tuned or synched, go to task 18-4.12. The radio from which a call is initiated the following will occur: preamble tones will be heard, wait until they cease before communicating; when link is established a short gong tone sounds in headset, LINKED is displayed and headset audio is restored. If this calling sequence does not occur, go to tasks 18-4.13 and 18- .14. If after a period of inactivity the link is not broken, go to task 18-15. When a call is being received RCVING PREAMBLE is displayed before communications from the calling station is heard. If RCVING PREAMBLE is not displayed go to task 18-4.16. If communications is not received from calling station, go to task 18-4.10. All preprogrammed information, including datafill and keyfill data, will be erased. The HF Control (4) will display ZEROIZED. If ZEROIZED is not displayed, go to task 18-4.17. GO TO THE NEXT PAGE 18-104 Change 21