High frequency (HF) Communication system

High frequency (HF) Communication system

The HF Communication system provide amplitude nodulation & single side band voice communication between aircrafts and ground or other carets The frequency range of this system is from 2 to 3C MHZ but nest communication stations are in the range from 2 to I8 MHZ system id used for long distance communication (sky wave propagator) The O/P from HF system is also directed to sacral decoders for Air traffic control signals. 

 

Each HF system consists of transceiver, antenna, antenna coupler, heightening arrestor, control panel & necessary relays.

1- Transceiver:-

The transmitter, section operates in a frequency range of 2 to 30 MHZ by me are of frequency selector witches on control panel. Amplification & nodulation (AM or SSB as required) are made on the mice audio.

The receiver operates at the sane channels. The receiver is a crystal- controlled superheat dyne.

2- Antenna coupler:-

Antenna tuning for all transmission frequencies is accomplished automatically by means of an antenna coupler system.

The complete antenna coupler system consists of a lightening arrestor remote coupler unit, coupler controller.       

Initial adjustment of the antenna coupler unit begins when ever a new frequency is selected for the transceiver, during the transceiver tuning cycle; a signal is seat to the antenna – coupler control which focuses Tuning circuits in the antenna coupler to drive to a home position. 

When the transmitter is tuned for transmitting, a sensing coupler to operate & adjust the impedance latch between the antenna & the transmission line so that the amount of reflect power is at a minimum. the sensing & tuning circuits operate  at all times that the transmitter is  operating & therefore continuously  provides  optimum  match between antenna & line, The tuning unit will match any combination of antenna resistance & reactance  to  the characteristic impudence -transmission line  at any  carrier frequency from2 to 30 MHZ

3-Control Panel:

Control panel of HF system consists of frequency selection, selector, and volume control.

4-HF antenna: -

The design of HF antenna varies with the size & shape of the aircraft. Aircraft cruise below 300 M.P.H. generally uses   a long wire antenna. Higher speed aircraft have specially designed antenna probes impelled the vertical Stabilizer.  Regardless of the Typo of antenna, a tuner is used to match the impedance of the transceiver to antenna.