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Thread: Radio transmission gremlin

  1. #1
    Kahle76's Avatar
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    Sep 2013
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    Jackson, MO
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    Default Radio transmission gremlin

    I am trying to finish my IV with a 582 and am getting a crackling sound during transmission at 4000 or more RPMs. No noise at lower RPMís and if the engine is off. The radio is a used Val Com 760 TSO that came with the multiple boxes of parts when I bought the project. I tested the antenna and coax while engine is running using a handheld instead of my ratio and no issues. Last month I had a friend add some ferrites to the wires because prior to adding them the transmission was full of static and unrecognizable. The ferrites remove 98% of the static noise. At the suggestion of another forum member, we wired a .05 capacitor from the power wire to the ground wire that feeds the radio to remove the crackling sound at the higher RPMís with no improvement. Any suggestions on getting rid of the crackling noise at higher RPMís?

    Thanks
    Mike Kahle
    Jackson, MO
    IV Classic Project

  2. #2

    Join Date
    Mar 2019
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    Morris, IL
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    176

    Default Re: Radio transmission gremlin

    Have you checked for ground loops? ie: multiple ground paths to the radio? Are the ring portions of your headset and microphone jacks grounded to the airframe and feeding back to the radio? Do your radio and intercom ground to the same point? Are you using a common ground location?

  3. #3
    Kahle76's Avatar
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    Default Re: Radio transmission gremlin

    Quote Originally Posted by 109JB View Post
    Have you checked for ground loops? ie: multiple ground paths to the radio? Are the ring portions of your headset and microphone jacks grounded to the airframe and feeding back to the radio? Do your radio and intercom ground to the same point? Are you using a common ground location?
    I did check for ground loops and had a friend who is much more knowledgeable than I when it comes to electronics along with an A&P and we canít find an answer.
    Mike Kahle
    Jackson, MO
    IV Classic Project

  4. #4
    Birdseyeview's Avatar
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    Sep 2017
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    Oregon, Ill
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    Default Re: Radio transmission gremlin

    Another possibility: Do all your spark plugs have solid tips where the ignition wire connects? In the past I had mistakenly put plugs in my Rotax 503 (on my Quad City Challenger) with screw on tips and over time the tips came loose and started to arc inside at the threaded interface. This caused terrible static noise on the intercom.
    Larry Olson
    Kitfox Series 6 - building
    Tri-gear, smooth cowl
    912 ULS

  5. #5
    Kahle76's Avatar
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    Sep 2013
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    Jackson, MO
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    Default Re: Radio transmission gremlin

    Quote Originally Posted by Birdseyeview View Post
    Another possibility: Do all your spark plugs have solid tips where the ignition wire connects? In the past I had mistakenly put plugs in my Rotax 503 (on my Quad City Challenger) with screw on tips and over time the tips came loose and started to arc inside at the threaded interface. This caused terrible static noise on the intercom.
    The plugs with the solid tips have 2 hours on them and I replaced the spark plug boots.
    Mike Kahle
    Jackson, MO
    IV Classic Project

  6. #6
    Russell320's Avatar
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    Oct 2009
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    Chandler, AZ (P19)
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    Default Re: Radio transmission gremlin

    Try grounding the radio box itself back to your common ground.....not just the tray. Make sure all ground wire associated with that radio is also brought back to that common ground.
    Russ
    Model IV Speedster
    912UL IVO IFA
    RV6A
    Needle, Ball and Airspeed
    Maybe a little GPS

  7. #7
    BobRS's Avatar
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    Feb 2012
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    Albuquerque, NM
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    35

    Default Re: Radio transmission gremlin

    What coax are you using? If RG-58 try ordering RG-400 from Aircraft Spruce that is cut to and terminated to the length of your existing cables.
    https://www.aircraftspruce.com/catal...s/11-09202.php
    I had a lot of radio noise problems with RG-58 and all of it disappeared with the more expensive RG-400. I thew the kitchen sink at the problems too; ferrites, filter capacitor, checked all my grounds. Keep those but consider the RG-400 cable.

    I also added another ground plane sheet underneath my main antenna mounted to the boss behind the turtle deck but underneath the fabric covering. It's attached to the antenna's coax grounded base connection. John McBean stated that it would increase my radio's range....and it DID.

    BobRS
    Kitfox SS7, Rotax 914
    Albuquerque, NM

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