Radio System

BASIC RADIO SYSTEM

Radio System

Typical Radio System

How radio system works..A radio system transmits information to the transmitter. The information is transmitted through an antenna which converts the RF signal into an electromagnetic wave. The transmission medium for electromagnetic wave propagation is free space.The electromagnetic wave is intercepted by the receiving antenna which converts it back to an RF signal. Ideally, this RF signal is the same as that originally generated by the transmitter. The original information is then demodulated back to its original form.

RF Terms & Definitions RF Level

Attenuation (Fading)

Path Loss

Free Space Loss

There are few basic terms that we commonly used in Radio environment4

RF Terms & DefinitionsRF power level at either transmitter output or receiver input is expressed in Watts. It can also be expressed in dBm. The relation between dBm and Watts can be expressed as follows:

P(dBm) = 10 x Log P(mW) For example: 1 Watt = 1000 mW; P(dBm) = 10 x Log 1000 = 30 dBm P(mW) = 100 mW; P(dBm) = 10 x Log 100 = 20 dBm

For link budget calculations, the dBm convention is more convenient than the Watts convention.

RF Power Level

Radio frequency(RF) is a rate of oscillation in the range of around3kHzto300GHz, which corresponds to thefrequencyofradio waves, and thealternating currentswhich carry radio signals.dBThe dB convention is an abbreviation for decibels. It is a mathematical expression showing therelationship between two values.5

RF Terms & DefinitionsAttenuationReduction ofsignalstrength during transmission.Attenuationis the opposite of amplificationAttenuation is measured in dBIt is directly proportional to the frequency and distance of transmission. The general formula is given as:

Where, PR = Signal Power received by the receiver in Watts,PT = Signal power Transmitted by the transmitter in Watts.

RF Terms & DefinitionsPath Loss

RF Terms & DefinitionsPath LossPath loss is the loss of power of an RF signal propagating through space. It is expressed in dB. Path loss depends on:The distance between transmitting and receiving antennas.Line of sight clearance between the receiving and transmitting antennas.Antenna height.

Travelling = propagating8

RF Terms & Definitions

RF Terms & DefinitionsFree Space LossAttenuation of the electromagnetic wave while propagating through space. This attenuation is calculated using the following formula:Free space loss = 32.4 + 20xLog F(MHz) + 20xLog R(Km)where:-F is the RF frequency expressed in MHz.R is the distance between the transmitting and receiving antennas.

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RF Terms & DefinitionsFor exampleF = 2.4GHzR = 8KmTherefore:Free space loss = 32.4 + 20xLog (2.4x 103) + 20xLog (8) = 118dBwith R = 4KmFree space loss = 32.4 + 20Log(2.4x 103) + 20Log4 = 112 dB- Free space loss directly proportional with a distance

Line-of-Sight (LOS)Line-of-Sight whenspeakingof RF means more than just being able to see the receiving antenna from the transmitting antenna. In, order to have true line-of-sight no objects (including trees, houses or the ground) can be in the Fresnel zone. The Fresnel zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or elsesignal strengthwill weaken.