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By Lt NS Wickramasinghe Bsc E & E Eng
There are two basic type of electronic communication
COMMUNICATION
Simplex Duplex
One way communication information travels only one direction
Ex : Radio and Television
Two way communicationinformation travel in two direction
Ex : telephone
Electro Magnetic wave propagation in air can be divided in to Two
WAVE PROPERGATION
Longitudinal Transverse
There Are Two different ways which Electro Magnetic wavetravel from a Transmitting antenna to a Receiving antenna
RADIO WAVE
Ground wave Sky wave
Ground wave is radio wave travel along the surface of the earth.
They follows two distinct paths call Direct path and Reflected path
Sky wave often call Ionospheric waves radiated in upward direction and returned to earth at some distinct location due
to refraction
Skip distance is the distance from the transmitter to the point ware the sky wave is first routed to the earth size of skip distance depend on Frequency , Incident angle
and degree of ionisation
Amount of refraction in ionosphere depends on three factors
Density of Layer
Frequency of radio wave
Angle at which wave enter to the Layer
Troposphere- It has large variation
humidity and temperature but has only small effect
on electromagnetic wave at communication
frequencies.
Stratosphere- This has stable temperature
and humidity and has little effect on electromagnetic
wave at communication frequencies.
Ionosphere – This sphere has reasonably stable
temperature but contain Electron and Ionised gas and has major effect
on propagation of MF and HF.
Ionosphere is the uppermost part of theatmosphere it is ionised by the solar power orthe solar radiation. Ionosphere furtherclassified to D,E and F. During the day time Flayer split in to two as F1 and F2
The relationship between refraction index and
free electron density is defines as Maxwell’sequation and it is as follows
n = (1- 81N)f2
n- Refractive index
N- Free electron density
f- Frequency of the electromagnetic wave
As free electron density rise , refraction index falls. Hence refraction index varies with the F layer of Ionosphere
COMSETS
SN TYPE SEQUE NON SEQUE B/S H/H B/S H/H
01 VHF
Motorola XTL
5000
Motorola XTS
5000 Motorola Gm 338
Motorola GP
300
Motorola Astro
Motorola XTS
3000
Motorola Gm 300 ( X
)
Motorola GP
328 Motorola Spectra Cougar FM Q 52 (X ) VX 150 Cougar VX 168 HYT 3600 P 020 GP 2000
02 UHF
Motorola XTL
5000
Motorola XTS
5000 Motorola Astro Motorola Spectra 03 HF Transwold RT 7000 RT 100
Icom 718 (With
H/H) Chinees Transwold 04 DF(Rx) VR 5000 Icom 8500 DDF 6000 DDF6001
Listening and identifying radio frequencies transmitting by other parties.
The DF systems using various techniques such as ; Adcock, Doppler, Quasi-Doppler and associated multiple-element,
commutated (mechanical and electronic) arrays
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