What is the primary method of demodulation used by AM receivers compared with FM receivers?

What is the primary method of demodulation used by AM receivers compared with FM receivers?

• A. AM uses a detector, FM uses a discriminator
• B. AM uses a discriminator, FM uses a detector
• C. AM uses a limiter, FM uses a discriminator
• D. AM uses a detector, FM uses a mixer

Answer: (A)

In AM, the information sits in the envelope of the carrier, so the signal is recovered with a detector that rectifies and follows the envelope, typically an envelope detector made from a diode and an RC filter. In FM, the information is carried by the instantaneous frequency, so the demodulator converts those frequency changes into a voltage, using a discriminator (such as Foster–Seeley or ratio discriminator) to produce the audio signal. The limiter you sometimes hear about in FM front ends serves to keep amplitude constant so the demodulator responds mainly to frequency changes, but it isn’t the method used to demodulate—that role belongs to the discriminator. That’s why the statement that AM uses a detector and FM uses a discriminator best describes the primary demodulation methods.

In AM, the information sits in the envelope of the carrier, so the signal is recovered with a detector that rectifies and follows the envelope, typically an envelope detector made from a diode and an RC filter. In FM, the information is carried by the instantaneous frequency, so the demodulator converts those frequency changes into a voltage, using a discriminator (such as Foster–Seeley or ratio discriminator) to produce the audio signal. The limiter you sometimes hear about in FM front ends serves to keep amplitude constant so the demodulator responds mainly to frequency changes, but it isn’t the method used to demodulate—that role belongs to the discriminator. That’s why the statement that AM uses a detector and FM uses a discriminator best describes the primary demodulation methods.