(2)
The HF communication transceiver contains a transmitter and a receiver. The transmitter output is 125W in the AM mode and 400W pep in the USB mode.
(3)
Program pins on the transceiver determine the operating characteristics of the HF system. A program pin is provided to select an operating range from 2.000 MHz to 29.999 MHz or from 2.800 MHz to 23.999 MHz. A program pin is provided to select internal blower motor operation during transmit only or all the time electrical power is applied to the transceiver.
(4)
The transceiver front panel contains the following:
(a)
LRU FAIL light which comes on as a result of transceiver faults such as: 1) Low transmitter output power. 2) Low power supply voltages. 3) Frequency control board microcomputer failure. 4) Frequency synthesizer out-of-lock.
(b)
KEY INTERLOCK light which comes on as a result of HF comm antenna coupler faults such as: 1) HF comm antenna coupler internal power failure. 2) Excessive tuning time. 3) Extreme tuning reactance.
(c)
The HF transmitter is disabled when the KEY INTERLOCK light is on.
(d)
CONTROL INPUT FAIL light which comes on as a result of improper inputs from the control panel such as: 1) Lack of HF label code for the 32-bit control word input. 2) Invalid serial data input. 3) Insufficient repetition rate of HF data.
(e)
SQL/LAMP TEST switch, when pushed, provides a test condition where the following occurs: 1) LRU FAIL light comes on. 2) KEY INTERLOCK light comes on. 3) CONTROL INPUT FAIL light comes on. 4) Receiver audio squelch is disabled.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757 MAINTENANCE MANUAL
5) Radio frequency (rf) sensitivity line is grounded.
(f)
PHONE jack provides a receptacle for utilizing a headphone.
(g)
MIC jack provides a receptacle for utilizing a hand microphone.
(5) Each HF transceiver uses 115v ac 3-phase power from its respective HF COMM circuit breaker on the overhead circuit breaker panel, P11.
C. HF Communication Antenna Coupler________________________________
(1)
The left and right (if installed) HF communication antenna couplers (referred to as the antenna couplers) are located in the antenna coupler bay of the vertical stabilizer. The antenna couplers are rack-mounted, pressurized units weighing 17 pounds each. Each antenna coupler is pressurized with dry air at 5-7 psig.
(2)
The antenna coupler consists of rf tuning elements and control circuits which comprise a closed tuning loop. The antenna coupler is tunable over the frequency range from 2 to 30 MHz. Typical tuning time required is 2 to 7 seconds. The antenna coupler constantly monitors the rf transmissions to automatically adjust the tuning elements.
(3)
In dual HF installations, the antenna couplers are electrically interlocked so that only one HF system transmits at any time. Faults within the antenna coupler cause the KEY INTERLOCK light on the transceiver to come on. The following situations are considered faults:
(a)
Antenna coupler fails to home within 15 seconds of rechannel pulse.
(b)
Antenna coupler fails to tune within 15 seconds of RF application.
(c)
Internal arcing is detected.
(4)
Access to the antenna couplers is via access panel 322 CL on the left side of the vertical stabilizer. The panel is between the front and auxiliary spar and uses approximately 60 retaining screws.
D. HF Communication Antenna________________________
(1)
The HF communication antenna (referred to as the antenna) is built into the leading edge of the vertical stabilizer. The antenna is a shunt-fed slot-type antenna which is approximately eight feet long. An inverted U shaped insulative portion of the leading edge structure surrounds the antenna element on three sides.
(2)
The single antenna functions as the transmit and receive antennas for the HF system(s). The feedline connections from the antenna coupler mounting racks are at the lower edge of the insulative portion at the top of the antenna element.
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