Prepared By:RANA RAJ YADAV

29098

Presented toEr.parul AwasthiEr.Amit Katiyar

PRESETATION ON“ALL INDIA RADIO”

ANTENNA

FUNDAMENTALS

History The first license granted for transmitting a broadcast was

given on February 23, 1922. The Radio Club of Calcutta was the first radio club to start functioning in Nov-1924

The Government run broadcasting set up was called the India State Broadcasting Service (ISBS) which is then turned into AIR (All India Radio) in June 1936.

The introduction of the commercial channel ‘Vividh Bharti’ in October 1957 increased the interest and popularity of radio.

AIR today has a network of 277 broadcasting centres with 149 medium frequency(MW), 54 high frequency (SW) and 171 FM transmitters.

IntroductionWHAT IS AN ANTENNA?

Input Impedance

Radiation Efficiency

Different Field Regions

Power Gain

Polarization

Characteristics

Antenna Radiation Resistance

The input impedance Zin of an antenna is the ratio of voltage to current at its input terminals, where the power is fed to the antenna.

Zin = Ra + jXa, where Ra = Resistive part of impedance Xa = Reactive part of impedance Ra = Rr+Ri

Radiation Efficiency

• The radiation efficiency determines the effective transfer of power from the input to free space, and is given by

Rr Radiation Efficiency = ------------- Ri + Rr

Field Regions

The field regions are divide in three types • Reactive near-field

• Radiating near-field

• Far-field

Half Power (3 dB) Beam Width & Directivity

• The angle between the two directions in which the radiation intensity is one half (3 dB below) of the maximum value is called half power beam width.

• The direction of max. Radiation intensity is called the directivity of antenna

Power Gain of Antenna

• Unlike the isotropic antenna, any practical antenna has physical dimension.

• Extending this principle, very large power gain can be achieved in any plane by stacking a number of antenna elements in the perpendicular plane, in a particular way.

Polarisation•The plane containing the electric vector in the electromagnetic wave describes the polarisation of the radiated wave.

There are a number of well defined polarisation•Horizontal polarisation•Vertical polarisation •Circular polarisation•Dual polarisation•Elliptical polarisation

Aperture of an Antenna

•Aperture of a receiving antenna is the ratio of power delivered to the load to the incident power density. G λ² A= ------- 4 π• where G is the gain with respect to the isotropic anteena

Medium Wave Antenna

•Self Radiating MW Mast Antennas

•Top Loaded Antenna

•'T' and 'L' Antenna

Short Wave Antenna•The short waves (3 to 30 MHz) get attenuated very rapidly with distance if they travel close to the earth. •Dipole with centre fed arrangement is used.

•The impedance of single dipole is about 73 ohms.

F M Antenna

FM Antenna are two type

•Pole type

•Panel type

Conclusion

Now a days we use FM Antenna over AM Antenna

At same FM tower we can use FM and TV broadcasting

FM broadcasting in Omni directional

FM tower height we approx 100mt but AM tower is up to 100 to 150mt

Any Query ??

Thank You