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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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(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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23-11-01 Page 502 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/03
HF COMMUNICATION SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY
Airplanes with Collins 628T-2A Transceivers
1. General
A. Two high frequency (HF) communication systems are installed in the airplane. The HF communication system provides amplitude modulated and single sideband voice communication between airplane and ground or other airplanes. Communication is in the 2- to 30-MHz frequency range on any of 28,000 channels at 1 kHz spacing. Propagation characteristics of the HF band are most suitable for long distance communications.
B. Each HF communication system is composed of one transceiver, antenna coupler, and a single antenna. The HF control panel is installed in the forward electronic section of the control stand. A single flush-mounted antenna is located in the vertical fin leading edge. The antenna coupler is installed inside the vertical fin leading edge approximately under the antenna. The transceiver is installed on electronic equipment rack E2. The component locations are shown in Fig. 1.
C. The HF communication system control panel enables the desired communication channel to be selected and the system to be turned on or off. Sidetone is connected to the HF system audio switches in the flight interphone system. The antenna coupler unit matches the characteristic antenna line impedance to the impedance of the transceiver at the particular frequency on which the system is operating. Communication on the HF systems is completed through use of microphones and headphones of the flight interphone system (23-52-0).
D. The HF communication system uses 3-phase, 115-volt, 400-Hz ac and 28-volt dc power obtained from load control center P18. AC power is obtained through a single 3-phase circuit breaker.
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