Understanding how the Superhet / Superheterodyne Radio Works

The superhet or superheterodyne radio is over 100 years old - the first superhet receiver was made in 1918 and since then it has developed to become one of the most widespread types or formats of radio receiver ever.

The superhet or superheterodyne radio gains its name from the fact that it uses heterodynes above the audio radio - the word means supersonic, or above the audible range, and heterodyne, being mixed together. In other words the superhet radio concept is based around radio frequency mixers which are used to convert the frequency of an incoming radio signal to a fixed intermediate frequency.

This gives advantages in terms of filtering as fixed frequency filters are much easier to design and give much better performance. There are also advantages in terms of having the filtering at a lower frequency - particularly in the past it was possible to achieve a much better performance at lower frequencies. This is still true to some degree, but not to the same extent.

As the IF is where there is most of the gain, having a fixed frequency amplifier has a number of advantages. Also in the early days of vacuum tubes / valves, it was necessary to have a low frequency otherwise the amplifiers would burst into oscillation.

One major issue with the superhet radio is the image signal where there are two frequencies that can enter a mixer and provide an output at the intermediate frequency. The unwanted one is called the image signal and this is attenuated to a sufficient degree by adding tuning before the mixer.

More information about the superhet or superheterodyne radio can be found here: https://www.electronics-notes.com/art...

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