Direct and indirect method of fm generation pdf

1. What is direct and indirect method of FM generation?
2. What is meant by indirect FM generation?
3. Why indirect method of FM generation is preferred over direct method?

What is direct and indirect method of FM generation?

This method is called as the Direct Method because we are generating a wide band FM wave directly. In this method, Voltage Controlled Oscillator (VCO) is used to generate WBFM. VCO produces an output signal, whose frequency is proportional to the input signal voltage. This is similar to the definition of FM wave.

What is meant by indirect FM generation?

In the indirect method of producing frequency modulation, the modulating signal is first integrated and then phase modulates a crystal controlled oscillator signal to produce a narrow-band FM signal. Frequency multiplication is then used to increase the resulting frequency deviation to the desired level.

Why indirect method of FM generation is preferred over direct method?

The direct methods cannot be used for the broadcast applications. Thus, the alternative method i.e. indirect method called as the Armstrong method of FM generation is used. In this method the FM is obtained through phase modulation. A crystal oscillator can be used hence the frequency stability is very high.