CLASSIFICATION OF RADIO TRANSMITTERS ACCORDING TO THE CARRIER FREQUENCY

CLASSIFICATION OF RADIO TRANSMITTERS ACCORDING TO THE CARRIER FREQUENCY

According to this method of classification, transmitters may be classified as below

1) Long Wave Transmitters: These transmitters operate on long waves i e on frequencies below 300 kHz. Such long wave radio transmitters are used for broadcast in temperate countries, where atmospheric disturbances on long waves 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 transmitting aerial must be very large typically 100 kW or more.

2) Medium Wave Transmitters: These transmitters operate on frequencies in the range of 550 to 1650 kHz and are usually used for broadcast. Hence the band of frequency extending from 550 to 1650 kHz is commonly referred to as the Broadcast Band. The carrier power may vary from as low as 5 kW to as high as 500 to 1000kW.

3) Short Wave Transmitters: These transmitters operate on frequencies in the short wave range of 3 to 30MHz. In practice, frequencies beyond 24 MHz’ are not used. Ionospheric propagation of electromagnetic waves takes place at such short waves. The attenuation of radio waves travelling 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 1 to 10 kW For overseas broadcast certain amount of beaming of power is required to be done But inspite of such a beaming of energy; because of the large distance involved, the carrier power generally used is 10 to 1 00 kW. 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 5 kW or so.