Draw the block diagram of AM transmitter, explain its operation.

1 Answer

AM transmitter is of two types

i)High Level AM Transmitter ii)Low Level AM Transmitter


i) RF crystal oscillator: It is a source of carrier signal of desired frequency. The circuit is designed such that the frequency, amplitude and phase of carrier signal is constant. RF crystal oscillator generates pure unmodulated carrier signal.

ii)RF buffer amplifier: It is a unity gain amplifier having a very high input impedance and very low output impedance . It is used to avoid loading effect or in other words it is used for impedance matching. If RF crystal oscillator is directly connected to the RF power amplifier,  then due to loading effect, frequency of carrier signal may change.

iii) Class C power amplifier: It is a high power frequency class C amplifier. It is used to increase the power level of carrier signal. Class C amplifier is used because it has very high efficiency is greater than 70%.

iv) Modulator: Modulator is also a class C amplifier in which modulating signal of sufficient amplitude is added with the carrier signal to obtain amplitude modulated carrier signal. This high power high frequency AM signal is then applied to the transmitting antenna which radiates this AM signal into air or space. 

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