Sinads - what are they for?

[Phil]

I noticed the Sinad testers - it seems they are used for receiver testing - what type of receiver(s) and what type of tests? Just wondering if I should have one!

[Ramsey Tech Z99]

Phil,

This is directly from our SM1 manual, I think it will answer you questions.WHAT IS A SINAD METER?

If you’ve never heard of a sinad meter before, the first thing that you will probably say to yourself is “I don’t need it, let alone know what it is.” Well, if you do any type of radio repairs or service, chances are that you do. The good news is that the Ramsey SM-1 is really easy to use!

A sinad meter is a tool used to tune up or measure the sensitivity of a receiver. To perform a sinad test, a 1 KHz sine wave modulated on an FM carrier is injected into the receiver using a signal generator. Ideally, the received signal should be an identical 1 KHz sine wave. After all, your receiver is made to accurately demodulate any audio signal modulated on the carrier signal that it receives. If you were to tune or notch out the 1 KHz tone, you would not hear any other signal. In real receivers however, there is always a change in the received signal because of noise and the tuning of the receiver. One of the laws that made some guy named Fourier famous (not rich, probably!) is that every periodic (repeating) wave is made up of many sine waves at multiples of the original frequency. So a wave that comes out of your radio that is distorted or clipped will actually be made up of many sine waves at different frequencies.

Here’s the beautiful thing in all of that wave theory. Our sinad meter notches out the original 1 KHz signal and measures the level of what is left. This means that what the meter sees is all of those extra sine waves. Why do we want to know if they are there? Well, remember that if the receiver was perfect, there wouldn’t be any extra waves, called distortion, at all. By seeing how much distortion and noise remains after passing through the receiver, you can now adjust the receiver so that there is as little noise as possible, thus optimizing its operation.

[Phil]

Thanks - that explains it well - sounds like a great partner for a signal generator to ajust a receiver for best S/N and sensitivity.