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Thread: Strange Ammeter Readings

  1. #11
    Senior Member Dave S's Avatar
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    Default Re: Strange Ammeter Readings

    Jiott,

    I have been reading this post with a degree of intrigue..........and I haven't responded till now because my line of thinking might be percieved as voodoo........


    Your comment about the response from Dynon....."I submitted this "problem" to the Dynon tech support people and they think it is due to the RF energy from the radio interfering with the very sensitive ammeter sensor wires (unshielded). The sensor uses only a few millivolts/amp." I think has validity......although what they did not say, according to your post, exactly how or where the RF may be coming from.

    Here is my voodoo story.......none of our aircraft are exactly the same; and, consequently, none of our experiences are likely to be identical...... So.....when I was assembling our aircraft and doing final testing while not everything was quite complete...I was playing with the radio.....everytime I keyed & held the PTT.....the little red LEDs I had mounted up by the wing roots for nightime cockpit illumination came on!.....Voodoo because the LED wires were not yet connected to anything!....just the unshielded electrical wires laying across across the carrythrough tube by the front of the turtledeck. This was not my imagination...it happened......suspected cause.....the location of the com antenna behind the turtledeck was just a few feet from where the loose wires were laying was apparently enough to induce enough voltage in the wire to light up the LEDs (which have an extremely small draw in order to light up). With the LED feeds rerouted under the sheetmetal & connected to the buss/switch the issue went away - since I really, really wanted to have the LEDs come on at times in addittion to when the PTT was activated!

    With my little light voodoo story.....although different equipment is involved from your situation...you might consider the RF source interfering with the ammeter reading could be coming right off the exterior comm antenna and not from the antenna cable leading through the airframe. Might be just the way ammeter sensor wires are run through the aircraft in light of the fact that the whole aircraft is bathed in concentrated radiation from the comm antennae when the PTT is activated.

    Can't say that it is possible to diagnose stuff like this from a distance...lord knows we can't see RF waves with out eyes....just a thought for consideration.....The Dynon folks might be onto something with their RF interference comment.....location of the unshielded ammeter sensor wires might be worth considering....or using a shielded wire.

    Just a thought for consideration.

    Dave S
    KF 7 Trigear
    912ULS Warp Drive

  2. #12

    Join Date
    Sep 2014
    Location
    Thornton, CO
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    6

    Default Re: Strange Ammeter Readings

    Not a guru. Just my opinion.

    Your antenna system is probably not balanced. (pretty tough to do on a kitfox)
    The antenna is a series circuit so the current on each side (the whip and the ground plane) have to match and to do this your coax shield is probably an active element in the antenna system.

    Besides being an annoying signal on the sense lines of the ammeter it probably isn't all that good for your radio. (although they can deal with some reflection)

    A tuned ferrite toroid is a good idea. I would put it on the coax as near to the antenna as I could. Each trip a coax makes through a toroid will remove about 90% of the common mode signal (the reflected part) and none of the differential mode signal (the part you want to get to the antenna). to get 99.9% of the reflections removed you could wrap the coax through the same toroid 3 times or put 3 toroids in a row (maybe a 1/4 inch apart so they don't act as one detuned toroid.)

    THat's what I would try, 3 toroids on the coax near the antenna. Use shrink wrap, hot glue, rtv, electrical tape to fix them so they don't move about and make sure they are supported so as to not add strain on the coax run. I have seen them for sale on the MGL web site.

  3. #13
    Senior Member jiott's Avatar
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    Default Re: Strange Ammeter Readings

    Thanks Dave and John, I have been thinking about rerouting the sensor wires and using shielded wires. I also have been looking at ferrite toroids and snap-on beads. I plan to experiment with some of these methods. Will report on the results.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  4. #14
    Senior Member Esser's Avatar
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    Default Re: Strange Ammeter Readings

    At update on this Jim? My fuel pressure is going up when I use my PTT amongst several other little things.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  5. #15
    Senior Member jiott's Avatar
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    Default Re: Strange Ammeter Readings

    I installed two ferrite toroids and it didn't make any difference. I have just been living with it; it hasen't seemed to hurt anything.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  6. #16
    Senior Member PapuaPilot's Avatar
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    Default Re: Strange Ammeter Readings

    Quote Originally Posted by Esser View Post
    At update on this Jim? My fuel pressure is going up when I use my PTT amongst several other little things.
    Too bad it's not your fuel quantity.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  7. #17
    Senior Member Esser's Avatar
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    Default Re: Strange Ammeter Readings

    I fixed it. Rerouted my COAX and it went away.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  8. #18
    Senior Member efwd's Avatar
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    Default Re: Strange Ammeter Readings

    Nice Phil
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

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