✔️📘✏️HF communication system is a long-distance communication system and is used where the flight is out of the VHF service range i.e. (en-route phase of flight).
✔️📘✏️Long-range is achieved by using the sky waves which are refracted by the ionosphere to such an extent that they are bent sufficiently to return to earth.
✔️📘✏️The frequency range is 3-30Mhz.
✔️📘✏️ The narrow bandwidth of HF is overcome by SSB (Single Side Band) and reduced channel spacing which can be 1 kHz or even as less as 100 Hz.
✔️📘✏️HF communication system consists of a transceiver, RMP/RTP, antenna coupler unit and antenna.
✔️📘✏️The antenna coupler system is necessary to maintain an efficient match between the antenna and the transmitter at a wide range of frequencies.
✔️📘✏️The advantage of using the HF communication system over the VHF communication system is that it can transmit information over a long distance.
✔️📘✏️The antenna depends on the type of aircraft,
1. Light aircraft with low powered HF systems may have whip antenna.
2. Low-speed aircraft may have a long wire antenna.
3. Large aircraft have notch antenna which is a slot cut into the aircraft structure, often at the base of the vertical stabilizer, or a probe antenna which is fitted on the top of the vertical stabilizer.