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kesleyelectric(at)iowatel Guest
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Posted: Sat Oct 16, 2021 8:56 am Post subject: Transponder antenna ground plane |
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Greetings,
I’m preparing to install the ground plane for the transponder antenna on my steel tube fabric covered plane. It would be more convenient to mount the transponder antenna ground plane on the inside of the fuselage, on the bottom behind the baggage compartment. This would require a 7/8” thick spacer so the antenna would mount flush with the fabric. If I machined such a spacer from solid aluminum and made sure of low resistance connections between the spacer and the ground plane, would this adversely affect the antenna performance?
Any advice appreciated.
Tom Barter
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user9253
Joined: 28 Mar 2008 Posts: 1908 Location: Riley TWP Michigan
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Posted: Sat Oct 16, 2021 1:26 pm Post subject: Re: Transponder antenna ground plane |
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Read this thread:
http://www.matronics.com/forums/viewtopic.php?t=16762861
I would mount the transponder antenna to a 5.3 inch diameter ground plane.
Make sure the outer braid of the coaxial cable is electrically connected to the ground plane.
The antenna ground plane does not need to be electrically connected to the tubular steel airframe.
Wood could be used between the ground plane and airframe steel tubes to support the antenna where desired.
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Ceengland
Joined: 11 Oct 2020 Posts: 380 Location: MS
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Posted: Sat Oct 16, 2021 1:36 pm Post subject: Transponder antenna ground plane |
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On 10/16/2021 11:55 AM, Tom Barter wrote:
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Greetings,
I’m preparing to install the ground plane for the transponder antenna on my steel tube fabric covered plane. It would be more convenient to mount the transponder antenna ground plane on the inside of the fuselage, on the bottom behind the baggage compartment. This would require a 7/8” thick spacer so the antenna would mount flush with the fabric. If I machined such a spacer from solid aluminum and made sure of low resistance connections between the spacer and the ground plane, would this adversely affect the antenna performance?
Any advice appreciated.
Tom Barter
| Have you considered just flipping the assy over, so the xpndr spike points up? Fabric skin does little to attenuate RF, so if you can avoid punching another hole, why not? There might be a little 'shadowing' of the signal if you're too close to an aluminum baggage compartment, but I doubt you'd ever know without taking the plane to an 'antenna range' with a lot of expensive measuring hardware. I've heard of people putting them inside cowlings, and the uAvionix tech recommended that I mount their Echo UAT box, the WAAS GPS, and the antenna spike all on a plate within the fiberglass wingtip of my RV6. Obviously, there's much more shadowing by the wing rib than anything you'd see, and he told me that they have numerous examples flying that way.
To answer your actual question, extra aluminum on the back side of the ground plane should have no effect on the antenna's performance. Think of it as a much fatter, stronger 'bulkhead', as you would see inside aluminum skinned a/c near the xpndr antenna mount.
FWIW,
Charlie
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