What electronic circuit for communications receivers produces useful power at two or three times the frequency of the fundamental pulse rate?

What electronic circuit for communications receivers produces useful power at two or three times the frequency of the fundamental pulse rate?

• A. Tuning Circuit
• B. LC Tank Oscillator
• C. Use of Crystals
• D. Demodulation

Answer: (B)

Harmonic generation in a resonant RF circuit is the idea here. An LC tank oscillator uses a tuned resonant circuit—the inductor and capacitor store energy and ring at a specific frequency with high efficiency. When the oscillator’s active device drives the tank nonlinearly, the output contains harmonics—integer multiples of the fundamental pulse rate. Those harmonic frequencies, like twice or three times the base rate, can carry useful RF power in some receiver stages or be further multiplied to reach higher bands. The other options don’t do this as effectively. A tuning circuit sets or shifts the frequency but doesn’t produce appreciable power at harmonics. Crystals provide a very stable single frequency with little harmonic output. Demodulation is about pulling the information (audio/data) from the carrier, not generating RF power at harmonics.

Harmonic generation in a resonant RF circuit is the idea here. An LC tank oscillator uses a tuned resonant circuit—the inductor and capacitor store energy and ring at a specific frequency with high efficiency. When the oscillator’s active device drives the tank nonlinearly, the output contains harmonics—integer multiples of the fundamental pulse rate. Those harmonic frequencies, like twice or three times the base rate, can carry useful RF power in some receiver stages or be further multiplied to reach higher bands.

The other options don’t do this as effectively. A tuning circuit sets or shifts the frequency but doesn’t produce appreciable power at harmonics. Crystals provide a very stable single frequency with little harmonic output. Demodulation is about pulling the information (audio/data) from the carrier, not generating RF power at harmonics.