A R I A

HF

The HF Communications Subsystem provides voice and teletype communications through any of three 1000 watt single sideband HF transmitters and receivers. The units are tuneable over 280,000 discrete frequencies in the 2MHz to 29,000 MHz frequency range and are capable of simplex or full-duplex operation. Additional communications capability is available when a satellite terminal is installed in the HF position, allowing voice communication and data retransmission via communications satellites as previously described. The primary purpose of the HF Communications Subsystem during normal operations is to provide liaison with the Aircraft Operations Control Center (AOCC) for flight following and mission updates during aircraft deployments. During Apollo operations, the HF position also served as the interface between ARIA's spacecraft communications equipment and the HF net to the ground. The aircraft received uplinks from Houston through an HF ground station and retransmitted the voice to the spacecraft via UHF and VHF transmitters. Astronaut downlinks were received simultaneously by VHF and UHF receivers, then the best of the two sources were selected for HF "remoting" to the ground.

Credit: NASA
Editor: Randy L. Losey