Am modulator pdf

For that reason, the class C amplifier current pulses are smaller, thereby causing a lower amplitude carrier output. Hence amplitude modulated wave is obtained which is then transmitted through antenna. It is so named because RF carrier and the message signal both are provided to the base of the transistor. Search Search. Types of AM Modulators are listed below.

In actual circuits as shown in figure, how this condition is obtained? AF signal is applied to the AF driver transformer which varies the grid bias of both triodes in accordance to the message signal. The modulating voltage AF is in series with the negative bias. The modulating voltage is superimposed on the fixed battery bias. Therefore, the amount of bias is proportional to the amplitude of the modulating signal and varies at a rate equal to the modulating frequency.

The RF input voltages are superimposed on the total bias. The resulting plate flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. The application of these pulses to the tuned tank circuit will give amplitude modulation. Collector Modulator The output stage of the transmitter is a high power frequency class C amplifier.

Base Modulator It is so named because RF carrier and the message signal both are provided to the base of the transistor. Message signal is amplified and then superimposed on the fixed bias Vbb which varies in accordance to the message signal. Then this superimposed bias is provided to the base of the transistor through RFC radio frequency choke.

The RF carrier is also provided to the base of the transistor through coupling capacitor which is then superimposed with the message signal bias. This superimposed bias voltages control the collector current which is proportional to the amplitude of the message signal, hence this modulated waveform is coupled to the secondary of the transformer.

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