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ADS-B Ground Plane Question

 
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markfw



Joined: 28 Feb 2019
Posts: 26
Location: Seattle, WA

PostPosted: Fri Mar 27, 2020 2:10 pm    Post subject: ADS-B Ground Plane Question Reply with quote

I will be mounting a uAvionix echoUAT ADS-B antenna on the belly pan of my cub. The vendor says to keep it 1 meter from my transponder antenna, which is mounted 14" forward of the leading edge of my belly pan.

The pan itself is an isosceles triangle with a 15" base and a length of 32". The pointy part of the pan is oriented facing aft.

Thus I have to place my Rami blade antenna toward the narrow (aft) part of the belly pan to stay 1 meter away from the transponder antenna.

My problem is that at the location that is sufficiently far from the transponder antenna the belly pan has narrowed so that it does not provide the 5" diameter circular ground plane that is apparently required.

SO (after all that), my question is whether the ground plane is only the part of of the belly pan that is immediately adjacent to the antenna, or is it the whole belly pan?

A related question is whether I can "cheat" the antenna forward a few inches? Since antenna radiated power varies inversely with the square of the distance does that imply that I could move the antenna 6' - 8" closer to the transponder antenna without a significant problem?

I am just trying to establish what my boundary conditions are with respect to the antenna location.

Thanks.

Mark


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chasb(at)satx.rr.com
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PostPosted: Sat Mar 28, 2020 6:10 am    Post subject: ADS-B Ground Plane Question Reply with quote

Time: 03:15:12 PM PST USSubject: ADS-B Ground Plane QuestionFrom: "markfw" <markwheelermd(at)icloud.com (markwheelermd(at)icloud.com)>Mark,
Mark,

I mounted my uAvionix echoUAT ADS-B antenna on the belly of my RV-6A and just aft of the firewall. It is located less than 30 inches horizontally from the transponder antenna. Works like a charm.

Charlie Brame
RV-6A, N11CB
San Antonio

—————————————————————
I will be mounting a uAvionix echoUAT ADS-B antenna on the belly pan of my cub.The vendor says to keep it 1 meter from my transponder antenna, which is mounted14" forward of the leading edge of my belly pan.The pan itself is an isosceles triangle with a 15" base and a length of 32". Thepointy part of the pan is oriented facing aft.Thus I have to place my Rami blade antenna toward the narrow (aft) part of thebelly pan to stay 1 meter away from the transponder antenna.My problem is that at the location that is sufficiently far from the transponderantenna the belly pan has narrowed so that it does not provide the 5" diametercircular ground plane that is apparently required.SO (after all that), my question is whether the ground plane is only the part ofof the belly pan that is immediately adjacent to the antenna, or is it the wholebelly pan?A related question is whether I can "cheat" the antenna forward a few inches? Sinceantenna radiated power varies inversely with the square of the distance doesthat imply that I could move the antenna 6' - 8" closer to the transponderantenna without a significant problem?I am just trying to establish what my boundary conditions are with respect to theantenna location.Thanks.MarkRead this topic online here:http://forums.matronics.com/viewtopic.php?p=495455#495455


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user9253



Joined: 28 Mar 2008
Posts: 1514
Location: Riley TWP Michigan

PostPosted: Sat Mar 28, 2020 6:30 am    Post subject: Re: ADS-B Ground Plane Question Reply with quote

I would cheat, but only 3 or 4 inches. Move the antenna forward so that the
two antennas are about 36 inches apart. The ground plane does not have
to be a perfect circle. If the ground plane extends the correct distance in 3
equally spaced directions (120 degrees), that is good enough.


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DougW



Joined: 16 Sep 2015
Posts: 3
Location: Washington

PostPosted: Sat Mar 28, 2020 10:13 am    Post subject: ADS-B Ground Plane Question Reply with quote

Charlie,

I recently installed a vertical monopole antenna on the belly of my Glastar (haven’t had a chance to test it yet).  The instructions for the antenna specifically said NOT to use a circular ground plane (apparently it can set up some interference with the antenna function) and suggested using a rectangular shape to reduce the interference possibility.  The 5” dimension is a minimum, twice as large is more effective, but the benefits beyond that diminishes quickly.

In your situation, with the antenna very near the apex, the ground plane would probably act more like a foil ground with two foil ribbons both facing forward (essentially along the edges of your triangle. Doesn’t sound like a good arrangement to me.

I used a 10” square of .020 aluminum for my ground plane. Could you possibly do the same?  Either mounting the ground plane aft of your triangle, or near the apex if that option is not practical?

Doug Windhorn

From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Charles Brame
Sent: Saturday, March 28, 2020 7:10 AM
To: AeroElectric List <aeroelectric-list(at)matronics.com>
Subject: Re: ADS-B Ground Plane Question


Time: 03:15:12 PM PST US
Subject: ADS-B Ground Plane Question
From: "markfw" <markwheelermd(at)icloud.com (markwheelermd(at)icloud.com)>

Mark,


Mark,



I mounted my uAvionix echoUAT ADS-B antenna on the belly of my RV-6A and just aft of the firewall. It is located less than 30 inches horizontally from the transponder antenna. Works like a charm.



Charlie Brame

RV-6A, N11CB

San Antonio



—————————————————————
I will be mounting a uAvionix echoUAT ADS-B antenna on the belly pan of my cub.
The vendor says to keep it 1 meter from my transponder antenna, which is mounted
14" forward of the leading edge of my belly pan.

The pan itself is an isosceles triangle with a 15" base and a length of 32". The
pointy part of the pan is oriented facing aft.

Thus I have to place my Rami blade antenna toward the narrow (aft) part of the
belly pan to stay 1 meter away from the transponder antenna.

My problem is that at the location that is sufficiently far from the transponder
antenna the belly pan has narrowed so that it does not provide the 5" diameter
circular ground plane that is apparently required.

SO (after all that), my question is whether the ground plane is only the part of
of the belly pan that is immediately adjacent to the antenna, or is it the whole
belly pan?

A related question is whether I can "cheat" the antenna forward a few inches? Since
antenna radiated power varies inversely with the square of the distance does
that imply that I could move the antenna 6' - 8" closer to the transponder
antenna without a significant problem?

I am just trying to establish what my boundary conditions are with respect to the
antenna location.

Thanks.

Mark
Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=495455#495455


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markfw



Joined: 28 Feb 2019
Posts: 26
Location: Seattle, WA

PostPosted: Sat Mar 28, 2020 12:44 pm    Post subject: Re: ADS-B Ground Plane Question Reply with quote

Thanks everyone for your replies.

It seems that the consensus is that I need to be far enough forward to have 5" of belly pan on each side of the antenna, which for me would be about 32". And, for at least one person, that distance worked.

This helps me establish the boundary conditions that I was looking for.

Mark


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