Design an Armstrong indirect FM modulator to generate an FM signal with a carrier frequency 98.1 MHz and a frequency deviation △f = 75 kHz. A narrow-band FM generator is available at a carrier frequency 100 kHz and a frequency deviation △f = 10 Hz. The stock room also has an oscillator with an adjustable frequency in the range of 10 MHz to 11 MHz. There are also plenty of frequency doublers, triplers, and quintuplers (which means the frequency multiplication ratio must be integers like 2n × 3 m × 5 k ).

In the Armstrong method of FM generation, the phase of the carrier is directly modulated in the combing network through summation, generating indirect frequency modulation.

Very high frequency stability is achieved through Armstrong method since the crystal oscillator is used as carrier frequency generator.

Please kindly check attachment for the step by step solution of the given problem.

Answer Link