23-12-00  DUAL HIGH FREQUENCY SYSTEM Back

A. System Function

The Dual High Frequency (HF 1 and HF 2) system (the system) permits long-range voice communication with ground stations or other aircraft that have HF equipment. The system operates in the 2.0000 MHz to 29.9999 MHz frequency range. The dual system includes two HF radio controllers – HF 1 and HF 2. HF 1 is located in the flight compartment and HF 2 is installed in the mission console.

The HF 1 controller and the HF 2 controller can receive at the same time, but the two controllers cannot transmit at the same time. The HF controller being used to transmit has the priority.

A Selective Calling (SELCAL) (Ref. 23-21-00) decoder unit is installed with the Dual High Frequency system.

B. System Components of HF 1 and HF 2 system

The primary components on each HF system (Ref. Figures 1-6) are:

• HF controller (Ref. Fig. 1 and Fig. 4)
• Bus adapter (Ref. Fig. 2)
• Receiver/ exciter (Ref. Fig. 2)
• HF power amplifier/ antenna coupler (Ref. Fig. 2)
• HF Antenna (HF 1 and 2 systems use the same HF antenna) (Ref. Fig. 3 and Fig. 5)
• Bridging amplifier
• Dual external capacitor (only used on HF 1 system) (Ref. Fig. 2)
• HF transmitter (Tx)/ SELCAL switch indicator (only used on HF 1 system) (Ref. Fig. 1)
• HF transmitter (Tx) indicator (only used on HF 2 system)

C. System Operation (Ref. Fig. 6)The system changes audio input signals from the flight crew, the mission console operator, the forward and aft observers microphones, and transmits them at preset HF Radio Frequency (RF). The system changes the received HF RF signals to give audio outputs to the flight crew.