NOTE: WWV transmits on 5, 10, and 15 MHz. The RF signals are modulated by pulses at 1 Hz and also by standard audio frequencies alternating between 440 and 600 Hz. WWV transmissions are continuous except for a 4-minute interruption beginning approximately 45 minutes after the hour.
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(3)
Perform an approximate frequency check on the transceivers by listening to WWV with the mode selector switches in the USB and AM positions. Reception shall be satisfactory in all positions.
(4)
Using HF-1 system, select an authorized test frequency and press a microphone push-to-talk button. A 1000-cycle tone shall be heard during system tuning. WWV reception on HF-2 shall be interrupted and subsequent HF-1 tone or transmissions heard at first officer's station. WWV reception shall return when HF-1 system keying is released
(5)
Adjust RF SENS (RF gain) control on HF control panel to maximum. If subsequent tests reveal RF overloading is occurring, back off control to point where overload condition just disappears.
(6)
Tune HF system to several active channels and establish communication. Compare receiver sensitivity. Reception should be approximately equal on all channels. Check operation with mode selector switch in AM and USB positions. Communication shall be satisfactory in all positions.
(7)
Tune system to several different channels and ensure operation is good by channeling from both above and below the selected frequency.
NOTE: The tuner duty cycle is 5 minutes on and 5 minutes off on frequencies between 2 to 3 MHz. Excessive keying of system on low frequencies may cause 100°C overheat switch in tuner to fault system; wait 5 minutes and rechannel to reset system. Above 3 MHz the duty cycle is continuous.
(8)
Tune HF-1 system to an authorized test frequency. Key the system and establish communication. Check that the R/T FAULT lamp and KEY INTERLOCK lamp do not come on. Transmission and reception should be loud and clear. Sidetone should be clearly audible when transmitting. The retune cycle shall go to completion with the push-to-talk switch closed.
NOTE: If the R/T FAULT lamp or KEY INTERLOCK lamp comes on or flickers, a defective transceiver or coupler is indicated.
WARNING: DO NOT OPERATE THE HF COMMUNICATION SYSTEM WHILE THE AIRPLANE IS REFUELED OR DEFUELED. AN EXPLOSION CAN CAUSE INJURIES TO PERSONS AND DAMAGE TO THE AIRPLANE.
WARNING: MAKE SURE PERSONNEL STAY A MINIMUM OF 10 FEET (3 METERS) AWAY FROM THE HF COMMUNICATION ANTENNA WHEN THE HF SYSTEM TRANSMITS. RF ENERGY FROM THE HF COMMUNICATION ANTENNA CAN CAUSE INJURIES TO PERSONNEL.
(9)
Repeat steps (4) thru (8) using HF-2 system.
(10)
Secure HF systems.
(11)
Determine whether there is any further need for electrical power on the airplane; if not, remove external power.
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HF ANTENNA AND COUPLER - REMOVAL/INSTALLATION
EFFECTIVITY
AIRPLANES WITH FLUSH ANTENNA
1. HF Antenna - Removal/Installation (Fig. 401)
A. Removal
(1)
On P18 circuit breaker panel, open circuit breakers HF AC and DC.
(2)
Remove screws from antenna access door on leading edge of vertical fin and remove door.
(3)
Remove nut, securing electrical feedline tube to antenna conductor.
(4)
Remove bolts securing antenna (vertical fin leading edge) to aircraft structure, and remove antenna.
B. Installation
(1) Verify that circuit breakers opened in Step A(1) are open.
NOTE: The HF flush antenna includes a fiberglass section on the fin leading edge which is covered with a rain erosion coating. This coating will require replacement, with the frequency of replacement dependent upon the operator's erosion environment.
CAUTION: THE METAL LEADING PORTION OF THE FIN SHOULD NOT BE COATED WITH RAIN EROSION COATING BECAUSE OF LIKELY DETRIMENTAL EFFECTS ON THE HF SYSTEM PERFORMANCE.
(2)
Place antenna into mounting position. Guide antenna conductor into place between electrical straps as antenna is positioned (Fig. 401).
(3)
Align holes in antenna conductor and electrical straps and secure with bolt, washer, and nut.
(4)
Secure antenna to aircraft structure with bolts.
(5)
Install antenna access door.
2. HF Antenna Coupler - Removal/Installation (Fig. 401)
A. Removal
(1)
On P18 circuit breaker panels, open circuit breakers HF AC and DC.
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