HF Communication PDF

HF COMMUNICATION  INTRODUCTION The HF communication system is used for long distance communication. HF communication systems are installed on many long distance aircraft for worldwide communication.  In modern aircraft types the SATCOM system replaces the HF system because it guarantees a...

HF COMMUNICATION  INTRODUCTION The HF communication system is used for long distance communication. HF communication systems are installed on many long distance aircraft for worldwide communication.  In modern aircraft types the SATCOM system replaces the HF system because it guarantees a reliable long distance communication.  HF SYSTEM COMPONENTS Usually 2 independent HF communication systems are installed in long distance aircraft. Each system has a transceiver which is located in the avionics compartment and an antenna which is usually located in the leading edge of the vertical stabilizer. An antenna coupler is needed to tune the antenna to the selected HF frequency. HF SYSTEM COMPONENTS LOCATION The HF transceiver has a transmitter and receiver that functions in the same way as the VHF transceiver. Transmission happens with an output power of 200W – 400W. The frequency and system selection on the RMP is done in the same way as for the VHF system. With the AM pb on the RMP you can select 2 different operational modes for HF When the pb is pressed the first time, the AM mode is selected. this mode transmits the modulated signal via a carrier.  When the pb is pressed again, the default SSB mode is selected. SSB stands for single side band. This mode transmits the modulated signal without a carrier giving better transmission efficiency. With the HF sensitivity selector knob on the RMP you can adjust the sensitivity of the reception. Note that some RMP types have a SQL knob instead. Here you can select the squelch level which is the level for noise suppression. On older aircraft types you can find a separate HF control panel with the same control functions as described for the RMP  The antenna coupler must tune the antenna to the selected HF frequency before you can start any transmission. Reception is always possible without a new coupler tuning. Pressing briefly one of the PTT switches for the first time will start the tuning.  You can hear a 1 KHz tone as long as the tuning lasts. You can monitor the correct transmission with the sidetone when normal transmitting power is available. HF SYSTEM OPERATION (STEPS TO ESTABLISH HF COMMUNICATION)  With the 1st step the audio equipment had to be connected to the transmission and reception channel of HF no.1  HF system no.1 has to be selected to AM mode on the RMP  The selected frequency is now shown in the standby frequency window. When the frequency is activated, you must first check if this frequency is busy before you start a transmission Let us assume that no communication is in progress, so that you can start tuning the antenna coupler Pressing the radio transmission or PTT sw the first time after a new frequency selection, tunes the transmitter and the coupler to the new frequency When the tuning tone has stopped, you can start your communication with the selected ground station.