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Thread: Transponder noise?

  1. #21
    Senior Member
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    Default Re: Transponder noise?

    Hi Andy
    I was unable to figure out how to wire in the PMI intercom when I installed the new ICOM. That is why I went with the built-in.
    Good luck.
    Don

  2. #22
    Senior Member jtpitkin06's Avatar
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    Default Re: Transponder noise?

    Andy,

    Is your audio input jack isolated from ground with shouldered fiber washers?
    If it grounds, even with nothing plugged in, it can create a ground loop.

    I'm looking at the wiring diagrams to search for other sources of noise. Give me a day or two.

    John Pitkin

  3. #23
    Senior Member jtpitkin06's Avatar
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    Default Re: Transponder noise?

    Andy,

    If you have a hand mic jack, in addition to the headset mic jacks, the barrel must be grounded back to Point A (Mecca)

    The Sig wiring diagram does not show a connection to the hand mic barrel.

    Try installing a .01mfd capacitor acrpss J1 pins 7 and 4 [red and black] to smooth out input power noises.

    The only thing I can suggest from here is to get an oscilloscope and look at the power supply voltage coming into the unit. Place the probe on the 12 volt input with the scope set to AC. You should see no more than 5 milivolts ripple. Note the frequency of the ripple and see if it varies with the engine RPM. [alternator noise]

    Other than that you're going to need local help. I'm sorry we can't fix it over the internet. Some things you just have to be there.

    JP

  4. #24
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    Default Re: Transponder noise?

    MGL has EMI Suppressors for sale on their site for this problem, along with a handy guide to solve this type of problem. Would this be a good fix?

  5. #25
    Senior Member jtpitkin06's Avatar
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    Default Re: Transponder noise?

    SD7,

    Ferrite beads can be effective when there is a direct link from the transmitter via an audio cable to the intercom. In this case the offending noise is in sync with the transponder, which has no audio cable. A ferrite bead on the transponder ground alone might help, but would not likely be effective. One could certainly try it as the beads are cheap. MGL does not have a lock on ferrite beads. Go to Digikey or Mouser. Even Radio Shack has them.


    There is some evidence of an offending ground loop somewhere in Andy's system. Other noises are reported to be audible. Finding the ground loop is the problem. It can be as simple as a phone jack body rubbing the frame or an improper ground. When found, there is usually one of those “AHA!!!” moments.

    Other than coaching someone through on common installation errors, it is almost impossible to diagnose a ground loop problem via emails or forums. You really need to be there with a scope and a meter. Once the common errors are exhausted, it’s time to get help or go to the Avionic$ $hop.

    John Pitkin

  6. #26

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    Default Re: Transponder noise?

    Andy,
    Since this thread died out, i'm assuming you found the source of the problem. Was it the unshielded PTT wires? I have the identical problem in my aircraft, using different components, and hope whatever your fix was will save me some searching time... thanks in advance!

    Justin

  7. #27
    Senior Member akarmy's Avatar
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    Default Re: Transponder noise?

    Alas, I have not yet solved it for myself. I guess I got lazy and said
    "eh, it ain't that bad" and have ignored it for the time being. I got as far as tracing down the ground leads, all manor of transponder and com antenna cabling and routing, replaced the transponder with another known working unit and have still not found the source as of yet. I do notice that it's worse sometimes and then better at other times. I've wondered if it could be my intercom being the problem, but I doubt it. Like others have pointed out it's most likely somewhere in the wiring or shielding / grounding.

    Good luck in tracking it down. I guess I'll wait for you to find the next clues and then maybe start working on mine again.
    Andy Karmy
    Kitfox 7 - 912S - SOLD
    Auburn, WA

    http://kitfoxflying.com

  8. #28

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    Apr 2013
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    Default Re: Transponder noise?

    Bummer!
    Subsequent flights seem to point to the ANR circuitry on my BOSE headset. It's still inconclusive, but the problem "went away" over the last 3 flights. Then on the most recent, I had forgotten to activate the ANR prior to takeoff, then when it powered on the interference was back. It quit when I shut down the ANR and didn't come back on subsequent restarts, so....

  9. #29
    Senior Member akarmy's Avatar
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    Default Re: Transponder noise?

    Do you have your Bose headsets powered via the plane power, or batteries? If Plane powered, then maybe a grounding issue with the power supply to them?

    These noise issues are hard to find that's for sure. Mine comes and goes these days. I've learned to ignore it for now.
    Andy Karmy
    Kitfox 7 - 912S - SOLD
    Auburn, WA

    http://kitfoxflying.com

  10. #30

    Join Date
    Apr 2011
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    Jax, FL
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    Default Re: Transponder noise?

    I was searching for radio noise and came across this post. I am having a similar problem with my kitfox IV. I have a rotax 912 and a Val 360 comm. I bought 3 ferrite beads. I placed them as follows:
    1. on the positive side of the capacitor near the relay
    2. second one on the lead to the power bus
    3. third one on lead from the power bus to the radio.

    I monitored the transmitted signals on my headheld with ear buds under my David Clarke ANR headset. Definite improvement but now I am hearing a fast thumping noise in my headset. Still researching and working the problem. i have had the aircraft for about year and the problem developed shortly after I bought and got so bad that my transmissions were unreadable. Could the capacitors be a problem?
    regards
    John McGlynn KCRG Jacksonville, FL

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