Generation of Amplitude Modulation (AM).

The device which is used to generate an amplitude modulation (AM) wave is known as amplitude modulator. The methods as amplitude modulator Generation may be broadly classified as following:-

1) Low level AM Modulation.

2)High level AM Modulation.

1)Low Level Amplitude Modulation:-

Figure shows  the block diagram of a low level AM modulation system. In a low level amplitude modulation system, the modulation is done at low power level. At low power levels, a very small power is associated with the carrier signal and the modulation signal. Because of this the output power of modulation is low. Therefore the power amplifiers are required to boost the amplitude modulated signals up to the desired output level.

 From block diagram in figure it is clear that modulation is done at low power level. After this the amplitude modulated signal is applied to a wide band power amplifier . A wide band power amplifier is used just to preserve the sidebands of the modulated signal. Amplitude modulated systems , employing modulation at low power levels are also called low level amplitude modulation transmitters.

Square-law diode modulation and switching modulation are examples of low-level modulation.

2)High level Amplitude Modulation:-

Figure  shows the block diagram of a high level AM modulation system. In a high-level amplitude -modulation system, the modulation is done at high power level. Therefore, to produce amplitude modulation at these high power levels, the base band signal and the carrier signal must be at high power levels. In block diagram of figure the modulating signal and carrier signal are first power amplified and then applied to AM  high level modulator. For modulating signal the wide band power amplifier is required just to preserve all the frequency components present in modulating signal.

On the other hand for carrier signal , the narrow band power amplifier is required because it is a fixed frequency signal. The collector modulation method is the example of high level modulation. Before we discuss low level and high level modulation methods in detail, we shall establish the fact that a non- linear resistance of non linear device can be made to produce amplitude modulation when two different frequencies are passed together through it.