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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