FM deviation measurement

This topic contains 1 reply, has 2 voices, and was last updated by Fred Kemmerer Fred Kemmerer 1 year, 6 months ago.

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  • #5764
    Mike Ryan
    Mike Ryan
    Participant

    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.

    - Mike (K1WVO)
    Nashua Area Radio Club

    k1wvo@arrl.net
    Visit us on the web at - https://www.n1fd.org

    #5774
    Fred Kemmerer
    Fred Kemmerer
    Keymaster

    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,

    - Fred (AB1OC)
    President, Nashua Area Radio Society

    ab1oc@arrl.net
    Visit us on the web at - https://www.n1fd.org

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