FM deviation measurement

[Nashua Area Radio Society]

I was asked about how to measure and adjust FM deviation on a VHF/UHF transmitter by one of our club members before yesterdays club meeting. He had a spectrum analyzer available to observe the radio with.

I indicated that I did not recall using this approach in the past, but had used a commercial FM deviation monitor. The monitor was basically an FM receiver with a peak AC detector wired to the output of the FM discriminator before the FM de-emphasis network that couples the discriminator output into the audio amplifier stage.

My suggestion was for him to make a quick search on Youtube as so many folks are quick to share practical information and ideas there. This morning, I made a quick check and came up with the following W2AEW video links:

https://www.youtube.com/watch?v=8IBOYoIV5m8 Bessel Null Method
https://www.youtube.com/watch?v=Nw3_w1HrlEs Spectrum Analyzer Estimation

There are many other links that were available with the Youtube Search Term: “fm deviation monitor”.

NOTE: The radio transmitter Manufacture’s maintenance manual will usually describe their recommended test setup and procedure for making this adjustment correctly. The manual will also provide additional insights into Test Point and Component locations that can save you a lot of time and help minimize surprises.

[Fred Kemmerer]

Hi Mike,

 

This is really good information, thank you! Would you mind turning this into an article on our Blog? I think that logs of folks would benefit from the information that you shared here. Thanks!

73,

[Author]

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