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Thread: Radio Whine Troubleshooting

  1. #11
    moto657's Avatar
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    Aug 2018
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    Canyon Lake, CA
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    Default Re: Radio Whine Troubleshooting

    Quote Originally Posted by tnowak View Post
    Do you get interference under this scenario?:
    1. Intercom off.
    2. Only one headset plugged in.
    3. All electrics off, except for radio on.
    4. Engine off
    Any interference? No. Only the quiet whine from the Radio display if it is full bright

    Then try this scenario?:
    1. Intercom off.
    2. Only one headset plugged in.
    3. All electrics off, except for radio on.
    4. Engine running but alternator off.
    Any interference? No. Only the quiet whine from the Radio display if it is full bright
    Then try this scenario?:
    1. Intercom off.
    2. Only one headset plugged in.
    3. All electrics off, except for radio on.
    4. Engine running and alternator on.
    Any interference? Yes. RPM tracking whine. See my above post for all of the sources of whine noise.

    TonyN
    Back to whine troubleshooting. OVR on my Interav alt failed, so I replaced it with an Plane Power 1224 VR. I was hoping it would cure the radio issues. No such luck. It made no change.

    Iíve done a little more testing. I have all jacks unhooked except pilotís headset. I tried grounding that to several different points, with no improvement to the whine.

    See my answers to Tonyís questions above in Blue

  2. #12
    tnowak's Avatar
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    Dec 2007
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    Hampshire, England
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    Default Re: Radio Whine Troubleshooting

    I think you may have a radio issue as increasing display brightness shouldn't introduce interference in your audio.
    I have downloaded and read the manual and it would seem that the 5 internal modules need good grounding/shielding so that radio interference is minimised.

    Quote: "The MX11 is comprised of five replaceable subassemblies. Three of the subassemblies contained in shielded modules to minimize radio frequency interference.
    Shielded modules include the COMM Receiver, COMM Synthesizer, and Transmitter."

    There was also reference to a modification to stop the radio producing interference that may affect ADF receivers.

    You may want to try temporarily adding a new ground wire from the airframe to the radio case just in case there is a main grounding issue.
    Also, look at your antenna coax to ensure that is in good condition and no corrosion where your antenna is attached to the ground plane (wing root fairing?).

    I looked at the wiring diagram as well and it didn't indicate screen mic wiring required but you probably need to use those fibre washers to insulate the mic jack from the panel/airframe.
    Did you try all avionics off (except radio), alt on and engine running but no mic connected; headphone only? Any audio interference?
    TonyN

  3. #13
    moto657's Avatar
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    Default Re: Radio Whine Troubleshooting

    Well, I still haven’t found the root cause, have a work around. I’ve found that if I turn the volume on my headsets way down and run the radio/ intercom volume near max there is almost no detectable whine noise. It’s working for now. I’ve just been enjoying flying! Put 50hrs on the Pacer in 2.5 months!

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