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Thread: ArTex 345 ELT - Ground Plane Question

  1. #1
    Senior Member Rodney's Avatar
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    Default ArTex 345 ELT - Ground Plane Question

    Need some help here on what to do about the Ground Plane for this ELT.

    I want to mount their included 24" antenna inside the Fox behind the baggage compartment.

    What do I do for a ground plane???

    Artex instructions call for a 48" diameter ground plane for the antenna.

    Called Artex Tech Support and he said he could not answer any questions regarding the ground plane for the antenna.

    I'm removing my old 121.5 transponder. It did not have an external antenna, so there is no existing antenna mount.

    Need the help of our electronics experts here on the forum.

    Thanks

    Regards
    Rodney

  2. #2
    Senior Member efwd's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    From my reading about the antennas, the airframe itself may be the ground plane. As I reported on my newly energized comm radio, my airframe is behaving like an effective ground plane to the best of my knowledge. Not flight tested of course. The ground plane can be simple wires run out from the center or it can be a disk. I contemplated installing a few radials of copper tape but so many people say that their antenna works fine having it mounted to the airframe itself.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  3. #3
    Senior Member Rodney's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    Thanks EFWD for the reply.

    I guess that is the only real option here. I'm certainly not an electrical type so I sure need some help here.

    All the ground plane calculators I can find indicate that the disk size needed is about 48 inches. Well, that isn't going to happen in any of our airplanes.

    I did find a 406 mhz dipole antenna, but it's another hundred bucks. Ouch - especially after buying the new elt.

    Some folks say you can ground it to the frame and others say you can't.

    I've searched this forum, but have not come up with a definitive answer yet.

    I know others here have installed the antenna inside the airframe to protect it in case of an accident. Just haven't found an answer yet I'm comfortable with.

    Anyone else ground the antenna to the frame???

    (Edit) So, I also checked AC 43.13-2B.310

    " Most antennas require a ground plane size
    of approximately 24" by 24". While the rule of
    thumb is to provide a minimum of 1/4 wavelength
    of the operation frequency, larger is better and
    ground plane symmetry is critical. Gaps in antenna
    coverage or performance may occur if a ground
    plane is not symmetrical. "

    OK - if I'm reading this right than I can construct a 1/4 wave ground plane
    disk - which would be about 14 inches in diameter and install the antenna on it.

    Is that the thing to do, or will grounding it to the airframe be sufficient??

    Rodney
    Last edited by Rodney; 09-12-2018 at 07:37 PM. Reason: adding new info

  4. #4
    Senior Member Esser's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    My 406 antenna is attached to a piece of aluminum the size of a deck of cards that is adel clamped to the frame. I then have a grounding wire attached to that plate. Seems to work fine.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  5. #5
    Senior Member jrevens's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    Josh's installation sounds about the same as mine, and also the same as a good friend who has a Mod. IV Speedster. FWIW, my friend had his accidentally triggered while his airplane was sitting on the ground and he didn't notice it until about 10 minutes later when the monitoring agency actually called him, so it worked just fine. I believe that there are quite a few installed that way in Kitfoxes. You definitely need to have a good airframe ground to the mounting surface and hence to the base of the antenna.


    This is what mine looks like, except I lowered the mounting plate position so that the tip of the antenna is below the surface of the cargo bay sack now.
    Attached Images Attached Images
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  6. #6
    Senior Member Av8r_Sed's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    I would take the approach outlined in the ArTex manual and use the adhesive strips under the fabric.
    Attached Images Attached Images
    -- Paul S
    Model III SN910
    582 IVO Med

  7. #7
    Senior Member Rodney's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    Thanks everyone for the help.

    Especially appreciate the picture John.

    Now I can fabricate my bracket and get on with the installation.

    Rodney

  8. #8
    Senior Member efwd's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    It must have been John that I copied when I installed mine.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  9. #9
    Senior Member aviator79's Avatar
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    Default Re: ArTex 345 ELT - Ground Plane Question

    Just for additional comfort, the frames from the factory now ship with an ELT and antenna bracket welded to the frame. You can see it in the background of this picture. I assume this is how it's done on the SLSAs, and there is basically no ground plane other than the frame.

    --Brian
    Flying - S7SS

  10. #10

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    Default Re: ArTex 345 ELT - Ground Plane Question

    John
    With the elt and elt antenna mounted in this position I’m curious where you mounted your comm antenna?
    Im building a KF5 and the plate for the comm antenna is where you mounted the elt mounting plate. And the kit we picked up came with a Comant CI-121 comm antenna that we would need to mount there. But I see the artex 345 manual reguires the elt antenna to be at least 32 inches away from the comm antenna.

    Joe Leeman
    KF5 912 uls
    Freedom, WI

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