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An Easy Guide to Understanding Classification Transmitters
According to this method of classification transmitters can be classifies as Long wave, Medium wave, Short wave, Very high Frequency , Ultra high frequency and Micro wave transmitters.
Long wave transmitters operate on long waves that are on frequencies below three hundred kilohertz. Such long wave radio transmitters are used for broadcast in temperate countries, where atmosphere disturbances on the long wave are not severe. Since long wave radio signals travel along the surface of earth and are rapidly attenuated, for reasonably high signal strength at the distant receiving aerial, the carrier power radiated from the transmitted aerial must be very large typically hundred kilowatt and more.
Medium wave transmitters operate on frequencies in the range of five fifty to sixteen fifty kilo hertz and are usually used for broadcast. Hence the band of frequency extending this is referred to as broadcast band.
Short wave transmitters operate on the frequency in the short wave range of three to thirty megahertz. In practice, frequencies beyond twenty four megahertz are not used. Ionosphere propagation of electromagnetic waves takes place at such short waves. The attenuation of radio waves traveling from the transmitting aerial to the distant receiving aerial though the ionosphere is small. Hence carrier power required to be radiated from the transmitting aerial is small. For national broadcast the carrier power used may vary from about one to ten kilo watts. For overseas broadcast certain amount of beaming of power is required to be done but in spite of such a beaming of energy because of the large distance involved, the carrier power generally used is ten to hundred kilo watts. For radio telephone working over long distances on short waves, highly directive transmitting and receiving antennas are used so that carrier power required may be relatively small, of the order of five kilo watts or so. Very high frequency and ultra high frequency transmitters operate either in very high frequency or ultra high frequency range and are used for frequency modulation broadcast, television broadcast, and frequency modulation radio telephony etc.
Microwave transmitters operate on microwave frequency that is frequencies beyond thousand mega hertz and are used in radar, television relay, and microwave link between two adjoining countries or between mainland and adjoining island etc. Thus the long wave transmitters are those which operate frequencies below three hundred kilo hertz. Medium wave transmitters are which operate between five hundred and fifty kilo hertz to one thousand six hundred and fifty kilo hertz while the short wave transmitters operate between three mega hertz to thirty mega hertz. The microwaves transmitters operate for frequencies beyond one thousand mega hertz.