Yaesu 991A audio hum

Discussion in 'General Technical Questions and Answers' started by AC3DB, Jun 30, 2021.

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  1. AC3DB

    AC3DB Ham Member QRZ Page

    My 991A makes a medium pitched hum that could be mistaken for a small cooling fan with my MD200 mic but not with the MD100 or stock yaesu hand mic. The MD200 mic does not make this hum with other radios. Years ago I bought a different 991A with an inrad studio mic (all new from DX) and I got that same funny hum, but the inrad mic did not make the hum with other radios, and that other 991A didn't make that funny hum with any other mics. There is something going on with my 991As that a certain mic combination makes this funny hum, but I wonder if there is a fix for it or has anyone else run into this? Aaron - AC3DB
  2. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Aaron:

    Sounds like a grounding problem between the mic and radio. Could it be 60Hz power line noise? If the mic and radio grounds were not well bonded, this could easily happen. I would use a multimeter to check ground continuity between the two.

    Brian - K6BRN
    AC3DB and KU3X like this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Could be 60 Hz, but that's "very low pitched," not "medium pitched," I'd think.

    Guess it depends on one's definition of medium-pitched. But if it's not a very low frequency like 60 Hz it may be some "digital" noise created by signals generated inside the rig and somehow being conducted into the mike line.
  4. K6BRN

    K6BRN XML Subscriber QRZ Page

    I assume this is a hum on the TX signal ... ?
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Maybe it just hums because it doesn't know the words?:)
    KB0QIP, AC3DB and K7JEM like this.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    Does the hum stop when you are not touching the mic ?
  7. AC3DB

    AC3DB Ham Member QRZ Page

    Nothing affects the noise, hi power, 1 watt, dummy load, grounding, dummy load... I wonder can I isolate something with a cap or transformer?

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