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Explain with block diagram of Armstrong method of FM generation.

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Explanation:- The crystal oscillator generates the carrier at low frequency typically at 1 MHz this is applied to the combining network and a 90o phase shifter. The modulating signal is passed through an audio equalizer to boost the low modulating frequencies for the reason discussed earlier. The modulating signal is than applied to a balanced modulator. The balanced modulator produces two sidebands such that their resultant is 90o phase shifted with respect to the un-modulated carrier The un-modulated carrier and 90o shifted sidebands are added in the combining network.  As discussed earlier, at the output of the combining network we get FM wave. This FM wave has a low carrier frequency fc and low value of the modulation index mf. The carrier frequency and the modulation index are then raised by passing the FM wave through the first group of multipliers. The carrier frequency is then raised by using a mixer and then fc and mf both are raised to the required high values using the second group of multipliers. The effect of multiplication and mixing is as discussed earlier. The FM signal with high fc and high mf is then passed through a class C power amplifier to raise the power level of the FM signal. 

Phasor Diagram:- 

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