What is a Demodulator?

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  • Written By: Patrick Roland
  • Edited By: A. Joseph
  • Last Modified Date: 03 October 2019
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A demodulator is commonly known as a radio tuner. It takes AM, FM and QAM signals and decodes them into an audio/video output. Demodulators have been used since the very first wireless transmissions and continue to be used today with internet modem technology. While modern demodulators are more complex, the act of demodulation has changed very little over the years.

A demodulator is a circuit that separates the Amplitude Modulation (AM), Frequency Modulation (FM) and Quadrature Amplitude Modulation (QAM) signals from the countless radio waves in our atmosphere and decodes the information from the carrier. A carrier is the signal sent from a source, such as a radio station or, in the case of walkie talkies or CB radios, another radio itself. The demodulator was first used before there were radio stations, back when Morse code was the main form of wireless communication. At that time, it was called a detector. These primitive devices did not need to convert the signals they found into audio signals, but only had to note the presence or absence of a radio wave.


The first type of audio signal the demodulator began working with was AM. An envelope detector and a product detector are two types of demodulators that help to pick up the carrier signal from an AM source. The envelope detector passed a current in one direction only, and its simplicity was exemplified by early crystal radio sets. A product detector multiplies the incoming signal with an oscillator signal. The resulting sound is often filled with static and unclear.

Compared to AM's basic setup, FM is much more complicated. FM demodulators come in many different types, but the Foster-Seeley Discriminator is the most popular. This type of electronic filter regulates its input frequency with its output frequency. The result is a much clearer sound than with AM and an easier signal to capture. This is why AM radio stations on a car radio might come in and out of tune as the car passes telephone poles and goes under tunnels and why FM stations do not.

Modern demodulators deal with QAM signals that pass through computer modems. This demodulator captures the carrier signals in the air and converts them to digital binary code. This is how computers are able to pick up wireless internet signals. Also, modern demodulators help receive UHF and VHF signals for television antennas.

Demodulators are the cornerstone of wireless technology. Their complexity varies from basic electronic simplicity to high tech complexity. From Morse code to FM radio and wireless internet, this technology has helped the world communicate.


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