Answer :
Final answer:
To design an Armstrong FM modulator to generate an FM carrier of 98.1 MHz with a frequency deviation of 75 kHz, an oscillator, signal multipliers, a narrow-band FM generator, frequency multipliers, and an adder are used.
Explanation:
To design an Armstrong FM modulator that generates an FM carrier of 98.1 MHz and a frequency deviation of Δf = 75 kHz, we can use a narrow-band FM generator of 100 kHz and a frequency deviation of Δf = 10 Hz. We also have an oscillator with an adjustable frequency of 10 to 11 MHz, as well as frequency doublers, triplers, and quintuplers. Here is a block diagram of the modulator:
- Oscillator (10 to 11 MHz) --> Signal multiplier (frequency quintupler) --> Signal multiplier (frequency tripler) --> Signal multiplier (frequency doubler)
- Narrow-band FM generator (100 kHz) --> Frequency multiplier (frequency quintupler)
- Adder
- Output (FM carrier of 98.1 MHz with a frequency deviation of 75 kHz)
The carrier frequency, fc, and frequency deviation, Δf, at each stage are as follows:
- Oscillator: fc = 10 to 11 MHz, Δf = 0 Hz
- Signal multiplier (frequency quintupler): fc = 50 to 55 MHz, Δf = 0 Hz
- Signal multiplier (frequency tripler): fc = 150 to 165 MHz, Δf = 0 Hz
- Signal multiplier (frequency doubler): fc = 300 to 330 MHz, Δf = 0 Hz
- Narrow-band FM generator: fc = 100 kHz, Δf = 10 Hz
- Frequency multiplier (frequency quintupler): fc = 500 kHz, Δf = 50 Hz
- Adder: fc = 600 to 605 kHz, Δf = 60 to 65 Hz
- Output: FM carrier of 98.1 MHz with a frequency deviation of 75 kHz
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