AM TRANSMITTER

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AM TRANSMITTER In an  AM  ( amplitude modulation )  transmitter  the amplitude (strength) of the carrier wave is varied in proportion to the modulation signal. In an FM (frequency modulation)  transmitter  the frequency of the carrier is varied by the modulation signal. There are two basic configuration for transmitters. High level modulation low level modulation  High level modulation In high power modulation signal,the carrier voltage is modulated at highest power level.the require power level is obtained by class c power amplifier.The block diagram of high level modulation as shown in fig(a). low level modulation In the low level modulation system, the carrier is modulated at low power level and the carrier power is subsequently raised to the desire level in the class B amplifier . transmitters using high power level are widely use at present .The block diagram of high level modulation as shown in fig(b). advantage AM sign
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HORN ANTENNA

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HORN ANTENNA

When a waveguide is terminated by a horn, such as many of those are shown in figure .1 the abrupt discontinuities  that exist at the edge are replaced by a gradual transformation. if incidence matching is correct, all the energy travelling forward in the waveguide will be radiated. Directivity will also be improved and diffraction reduced . There are several possible on configuration; three of the most  are show here. The  sectorial   horn  flares are out in the One Direction only and is the Is the equivalent of pillbox parabolic reflector. The pyramidal horn flares out in both direction and has the shape of truncated pyramid. The conical horn is similar to it and it does logical termination for circular waveguide if the   φ  figure (a). is it too small, resulting in a Shallow horn, The wave front leaving the horn will be spherical rather than plain, and the radiated Beam will be not directive.

fig.(1)

The flare angle is given by

φ =tan-1(h/2L)

The directivity of horn antenna is given by
D =7.5A/λ
WhereA=hw=area of horn mouth opening(aperture) and power gain 
GP =4.5 hw/λ^2

Advantage

-gain of the antenna is 25db
-low swr
-broad bandwidth
-simple construction

Application

-it is use as feeder
-it use as automatic door opener
-it us use in radar for short range




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