K54279 K54281
HF Communication System Component Location 5C8
23-11-01 Figure 1 (Sheet 1) Jun 20/85
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
5C8 HF Communication System Component Location
Jun 20/85 Figure 1 (Sheet 2) 23-11-01
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
3. HF Transceiver (628T-1)
A. The transceiver is used for airborne, narrow-band upper sideband (USB), voice and data communications. It is capable of transmitting (200 watts pep [peak envelope power] output in USB and 100 watts carrier) and receiving at 2.800 to 26.999 MHz on 24,200 channels with 1-kHz spacing. The transceiver consists of modules, subassemblies and a chassis assembly housed in a 3/4 ATR case. The function of the major modules and assemblies is as described below.
B. The frequency synthesizer generates 19.8 kHz, 69.3-MHz, and 72.6- to 96.799-MHz signals that are derived from a 9.9-MHz frequency standard. The 19.8-kHz signal is produced by a divide-by-500 circuit and is supplied to the power supply as a switching signal. The 500-kHz signal is produced by a phase-locked loop and is supplied as a carrier to the modulator and product detector in the receiver/exciter. A harmonic generator produces the 69.3-MHz signal that is used as a mixer injection signal in the receiver/exciter. The 72.6- to 96.799-MHz signal is produced by dual phase-locked loops and is also used as a mixer injection signal in the receiver/exciter.
C. The frequency module converts reentrant coded frequency data into bcd frequency data. Logic gates are used as decade decoders for the 1-, 10- and 100-kHz digits. A programmable read-only memory (PROM) is used as a decoder for the 1-and 10-MHz digits. The module also contains a frequency error detector and a frequency band decoder.
D. The receiver section of the receiver/exciter module is a completely solid-state, dual-conversion receiver that receives, amplifies, and detects incoming AM and/or USB signals from 2.800 to 26.999 MHz. The front end consists of a fixed tuned RF bandpass filter and an AGC-controlled RF amplifier. Frequency translation is accomplished using 72.6- to 96.799-MHz balanced mixers. Separate AGC-controlled IF sections are used for the AM and USB signals. The receiver has both receiver and SELCAL audio amplifiers. The exciter section is a completely solid state, dual conversion exciter that produces either USB or AME (full sideband) 2.800- to 26.999-MHz signals. The initial stages are a balanced modulator and 500-kHz if amplifiers. Frequency translation is accomplished using the same mixers that are used in the receiver section. A low-pass LC filter reduces spurious signals from being amplified in the ALC (automatic load control) controlled output RF amplifier.
E. The power amplifier amplifies the RF input from the exciter to a 200-watt pep level. Four stages of amplification are used, with both the driver and final amplifiers operated in push-pull configurations. Protective circuits produce the ALC signal, which is used to control the RF drive level to the input of the power amplifier. The final amplifier transistors are secured to conical-shaped mounts that fit into finned heat sinks. An internal blower provides cooling air for the power amplifier.
F. The low-pass filter module consists of six filters, directional wattmeter, motor control, a tune-in-progress attenuator, and the transmit-receive relay. A 3-deck motor-driven bandswitch selects the filter required for the selected operating frequency. The directional wattmeter consists of a forward power detector and a reflected power detector. These detectors produce dc analog signals that are representative of the measured RF power levels. The motor control contains transistor switches that control dc voltage applied to the motor.
5C8
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