Avionics bending: HF comm radio head

The HF (high frequency) communication system (referred to as the HF system) provides long-range air-to-ground or air-to-air communications. The HF system operates in the 2.800 to 23.999 MHz frequency range on 21,200 channels in either AM (amplitude modulated) or USB (upper side band) modes.

Two HF (high frequency) communication systems are installed on the airplane.

The left and right HF systems consist of two HF comm transceivers, two HF comm control panels, two HF comm antenna couplers and a single slot-type shunt-fed HF comm antenna. The audio, microphone and PTT functions of each HF system interface with the audio selector panels (ASP's) of the flight interphone system.

The left HF system utilizes 115v ac 400 Hz 3-phase power from the left bus. The right HF system utilizes 115v ac 400 Hz 3-phase power from the right bus. The LEFT HF COMM and RIGHT HF COMM circuit breakers are located on the overhead circuit breaker panel P11.

HF Comm Control Panel:

The left and right HF comm control panels (referred to as the control panels) are located on their respective side of the pilots' overhead panel P5. The control panels weigh approximately pounds and are self-contained, including power supply. Each control panel is dedicated to providing mode control, frequency selection, and RF sensitivity adjustment for its respective HF comm transceiver.

The front panel of the control panel contains a mode selector switch, two concentric frequency control knobs, LCD frequency display, and a RF sensitivity adjustment control. The function selector provides on/off control and the selection of the AM (amplitude modulated) or USB (upper side band) modes. The left frequency control selects the MHz and 100 kHz digits displayed on the frequency counters. The right frequency control selects the 10 kHz and 1.0 kHz digits on the frequency counter. The RF SENS control adjusts the signal sensitivity of the receiver circuits of the HF comm transceiver.

The control panel contains circuits which convert the mode and frequency selections into digital form. The control panel provides a 32-bit word to the HF comm transceiver in the ARINC-429 format.