How do we communicate in aircraft?
There is fundamental need for communication between :
(1) air crew and ground controllers
(2)among the air crew
(3)between air crew and passenger
The current situation is the VHF is used for short range communication while HF , is used for long range communication.
VHF-very high frequency
HF- high frquency
A large airlines, such as a boeing 747, carries three vhf and dual hf. in addition in such aircraft ,selective calling(selcal) facilities are provided. such that ground station can call aircraft either single or ingroups without the need for constant monitoring by the crew.and also use audio integrating system.
VHF COMM.- an aircraft vhf comm. tranceiver is comprised of either a single or double conversion superhet receiver and an AM transmitter . a modern set provided 720 channels at 25 khz spacingbetween 118 mhz to 135.975 mhz. unill recently the spacing was 50 khz giving only 360 channles.the mode of operation is simplex(s.c.s),one frequency and one antennafor both receiver and transmitter.
A single vhf installation consist of three parts namely-
1.controll unit,2.transceiver, 3.antenna. communication by vhf is essentially line of sight by direct space wave.
HF COMM.-the long range comm. is acheaved by use sky wave which are refracted by the ionosphere to such an extent thant they are bent sufficiently to return earth.
a typical large aircraft hf instalation consist of two system ,each of which comprise a tranceiver, contriller, tunning unit and antenna . each of the tranceiver are connected to the AIS for mic.
to be cont.......in Aircraft comm. -2