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kesleyelectric(at)iowatel
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 Posted: Mon Apr 11, 2022 7:49 am Post subject: Transponder antenna ground plane |
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Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna.
Any details on the dimensions best for the octagonal ground plane, or comments from those who have satisfactory performance from one, would be much appreciated.
Tom Barter
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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nuckolls.bob(at)aeroelect
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| Posted: Mon Apr 11, 2022 8:15 am Post subject: Transponder antenna ground plane |
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At 10:48 AM 4/11/2022, you wrote:
| Quote: | Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna.
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The 'ideal' stand alone ground plane takes
two popular forms. Perfectly circular where
radius of the disk is equal to 1/4 wave in free
space at the operating frequency. In the
case of transponders, that's 1090 Mhz.
300/1090 = 0.28 Meters for a full wave,
0.07 Meters for 1/4 wave or 2.7 inches.
So a disk 5.4" in diameter is indicated.
Aluminum is fine.
The 'best' ground plane is an 'infinite' conductor
like lots of aircraft metal skin . . . not an
option in your case.
Now, having described ideal ground planes,
know that overall performance of the antenna
isn't super critical. Ground radars can
sniff out a signal REFLECTED from the metal
of your airframe, it an certainly see a
directly transmitted signal measured in
tens if not over 100 watts.
I'm unaware of any rationale for shapes
other than circular. Would like to see
antenna range test data that supports
the suggestion.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Mon Apr 11, 2022 8:25 am Post subject: Transponder antenna ground plane |
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On 4/11/2022 11:14 AM, Robert L. Nuckolls, III wrote:
| Quote: | At 10:48 AM 4/11/2022, you wrote:
| Quote: | | Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. |
  I'm unaware of any rationale for shapes
  other than circular. Would like to see
  antenna range test data that supports
  the suggestion.
|
My rationale is, two straight cuts (square) instead of lots of work cutting a circle.
Then there's the mounting convenience, after fab.
Charlie
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kesleyelectric(at)iowatel
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| Posted: Mon Apr 11, 2022 10:57 am Post subject: Transponder antenna ground plane |
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Forgot to ask – should the ground plane be “grounded” to the fuselage as some suggest, should it be isolated from the fuselage, or does it make any difference?
Tom Barter
Kesley Electric, Inc.
Phone (319)-347-2462
Fax (319)-347-6607
kesleyelectric(at)iowatelecom.net (kesleyelectric(at)iowatelecom.net)
From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Robert L. Nuckolls, III
Sent: Monday, April 11, 2022 11:15 AM
To: aeroelectric-list(at)matronics.com
Subject: Re: Transponder antenna ground plane
At 10:48 AM 4/11/2022, you wrote:
| Quote: |
Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. |
The 'ideal' stand alone ground plane takes
two popular forms. Perfectly circular where
radius of the disk is equal to 1/4 wave in free
space at the operating frequency. In the
case of transponders, that's 1090 Mhz.
300/1090 = 0.28 Meters for a full wave,
0.07 Meters for 1/4 wave or 2.7 inches.
So a disk 5.4" in diameter is indicated.
Aluminum is fine.
The 'best' ground plane is an 'infinite' conductor
like lots of aircraft metal skin . . . not an
option in your case.
Now, having described ideal ground planes,
know that overall performance of the antenna
isn't super critical. Ground radars can
sniff out a signal REFLECTED from the metal
of your airframe, it an certainly see a
directly transmitted signal measured in
tens if not over 100 watts.
I'm unaware of any rationale for shapes
other than circular. Would like to see
antenna range test data that supports
the suggestion.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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http://www.matronics.com/Navigator?AeroElectric-List |
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Mon Apr 11, 2022 11:58 am Post subject: Re: Transponder antenna ground plane |
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The ground plane probably should be grounded to the fuselage for lightning
protection. But I don't think it matters for performance.
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Peter(at)sportingaero.com
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| Posted: Mon Apr 11, 2022 12:44 pm Post subject: Transponder antenna ground plane |
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Bear in mind that the transmitter requires the braid of the coax to be connected to the ground plane and the centre conductor to the antenna blade – which must be insulated from the ground plane. Any other grounding is irrelevant to the performance of the transmitter. For a metal skinned aircraft the ground plane is the fuselage.
Peter
From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Tom Barter
Sent: 11 April 2022 19:57
To: aeroelectric-list(at)matronics.com
Subject: RE: Transponder antenna ground plane
Forgot to ask – should the ground plane be “grounded” to the fuselage as some suggest, should it be isolated from the fuselage, or does it make any difference?
Tom Barter
Kesley Electric, Inc.
Phone (319)-347-2462
Fax (319)-347-6607
kesleyelectric(at)iowatelecom.net (kesleyelectric(at)iowatelecom.net)
From: owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com) <owner-aeroelectric-list-server(at)matronics.com (owner-aeroelectric-list-server(at)matronics.com)> On Behalf Of Robert L. Nuckolls, III
Sent: Monday, April 11, 2022 11:15 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Re: Transponder antenna ground plane
At 10:48 AM 4/11/2022, you wrote:
| Quote: |
Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. |
The 'ideal' stand alone ground plane takes
two popular forms. Perfectly circular where
radius of the disk is equal to 1/4 wave in free
space at the operating frequency. In the
case of transponders, that's 1090 Mhz.
300/1090 = 0.28 Meters for a full wave,
0.07 Meters for 1/4 wave or 2.7 inches.
So a disk 5.4" in diameter is indicated.
Aluminum is fine.
The 'best' ground plane is an 'infinite' conductor
like lots of aircraft metal skin . . . not an
option in your case.
Now, having described ideal ground planes,
know that overall performance of the antenna
isn't super critical. Ground radars can
sniff out a signal REFLECTED from the metal
of your airframe, it an certainly see a
directly transmitted signal measured in
tens if not over 100 watts.
I'm unaware of any rationale for shapes
other than circular. Would like to see
antenna range test data that supports
the suggestion.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Virus-free. www.avast.com
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nuckolls.bob(at)aeroelect
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| Posted: Tue Apr 12, 2022 7:45 am Post subject: Transponder antenna ground plane |
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At 01:57 PM 4/11/2022, you wrote:
| Quote: | Forgot to ask – should the ground plane be “grounded” to the fuselage as some suggest, should it be isolated from the fuselage, or does it make any difference?
|
>The ground plane probably should be grounded to the fuselage for lightning
>protection. But I don't think it matters for performance.
>
>--------
>Joe Gores
Agreed . . . and yeah, making the ground plane from
a hexagon or octagon cut our on a shear makes good
sense labor wise as opposed to cutting out a circle.
I was fixated on demonstrable performance as opposed to
practical convenience!
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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Eric Page
Joined: 15 Feb 2017
Posts: 245
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| Posted: Tue Apr 12, 2022 10:15 am Post subject: Re: Transponder antenna ground plane |
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I put transponder and ADS-B antennas inside the wings of my Kitfox. The ground planes were made from a piece of very thin galvanized steel flashing material that I sourced from Home Depot. I drew circles on the material in the required sizes, rough-cut the parts with hand shears, then shaped them to final size in a couple of minutes with a disc sander. The center hole was made with a step drill, then the parts were coated with primer. I removed primer from a small area around the center holes to ensure good electrical contact to the antenna. I think my total investment in the parts was about $4 and one hour of labor. A couple of varnished wood sticks and some structural epoxy mounted them securely inside the wings, well away from the spar tubes.
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| Finished transponder and ADS-B antennas with DIY ground planes, ready to install. |
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Tue Apr 12, 2022 2:34 pm Post subject: Re: Transponder antenna ground plane |
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Nice work Eric. Is the antenna on the bottom or top of the ground plane?
Does it matter?
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Eric Page
Joined: 15 Feb 2017
Posts: 245
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| Posted: Tue Apr 12, 2022 3:59 pm Post subject: Re: Transponder antenna ground plane |
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| user9253 wrote: | Is the antenna on the bottom or top of the ground plane?
Does it matter? |
In flight, the radiating elements (pointing up in the photo) will point down toward the ground, and the BNC connector will face up. Not sure about your second question, but I've only ever seen transponder antennas on the bottom of airplanes, pointing down.
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user9253
Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan
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| Posted: Tue Apr 12, 2022 6:41 pm Post subject: Re: Transponder antenna ground plane |
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Next year Canada is going to require aircraft flying in Class A & B airspace to be able to send transponder signals to satellites. This requirement can be met either through antenna diversity (the use of a top and bottom antenna) or with a single antenna that is capable of transmitting both towards the ground and up towards satellites.
I have never seen transponder antennas on top of airplanes either. But chances are that an antenna on top would work just as well as one on the bottom.
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Eric Page
Joined: 15 Feb 2017
Posts: 245
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| Posted: Wed Apr 13, 2022 6:38 am Post subject: Re: Transponder antenna ground plane |
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Yes, I seem to remember reading something about that. I have no plans to fly into Canada, but I wonder what will be required, hardware-wise, to satisfy their requirement. I presume you would need a transponder designed for multiple antennas. It looks like uAvionix's tailBeaconX satisfies the Canadians, but beyond that, I have no idea!
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nuckolls.bob(at)aeroelect
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| Posted: Wed Apr 13, 2022 8:22 am Post subject: Transponder antenna ground plane |
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At 09:41 PM 4/12/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>
Next year Canada is going to require aircraft flying in Class A & B airspace to be able to send transponder signals to satellites. This requirement can be met either through antenna diversity (the use of a top and bottom antenna) or with a single antenna that is capable of transmitting both towards the ground and up towards satellites.
I have never seen transponder antennas on top of airplanes either. But chances are that an antenna on top would work just as well as one on the bottom. |
The quater-wave, ground-plane antenna has a
radiation patter like shown in this illustration.
Very attenuated response 'below' the ground plane.
Probably even more attenuation on a 'large' ground
plane like an aircraft skin.
Looking at the elevation pattern we see the major
lobe is displaced about 30 degrees off the ground
plane . . . i.e. favoring ground based stations
when mounted upside down. Response out to the
horizon is only down 3db . . .
Talking to satellites? Got any links to
expand on that? I'm wondering what service is
expected to use xponder data . . . and for
what purpose.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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| Posted: Wed Apr 13, 2022 9:35 am Post subject: Transponder antenna ground plane |
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On 4/13/2022 11:17 AM, Robert L. Nuckolls, III wrote:
| Quote: | At 09:41 PM 4/12/2022, you wrote:
| Quote: | --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com> (fransew(at)gmail.com)
Next year Canada is going to require aircraft flying in Class A & B airspace to be able to send transponder signals to satellites. This requirement can be met either through antenna diversity (the use of a top and bottom antenna) or with a single antenna that is capable of transmitting both towards the ground and up towards satellites.
 I have never seen transponder antennas on top of airplanes either. But chances are that an antenna on top would work just as well as one on the bottom. |
   The quater-wave, ground-plane antenna has a
   radiation patter like shown in this illustration.
   Very attenuated response 'below' the ground plane.
   Probably even more attenuation on a 'large' ground
   plane like an aircraft skin.
   Looking at the elevation pattern we see the major
   lobe is displaced about 30 degrees off the ground
   plane . . . i.e. favoring ground based stations
   when mounted upside down. Response out to the
   horizon is only down 3db . . .
   Talking to satellites? Got any links to
   expand on that? I'm wondering what service is
   expected to use xponder data . . . and for
   what purpose.
|
It's just ADS-B, with a/c transmissions received by satellites. To the FAA: Can I get a 'duh...'?
https://aireon.com/resources/overview-materials/its-just-ads-b/
Charlie
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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