Today's Message Index:
----------------------
1. 08:49 AM - Transponder antenna ground plane (Tom Barter)
2. 09:12 AM - Re: Transponder antenna ground plane (user9253)
3. 09:15 AM - Re: Transponder antenna ground plane (Robert L. Nuckolls, III)
4. 09:25 AM - Re: Transponder antenna ground plane (Charlie England)
5. 11:57 AM - Re: Transponder antenna ground plane (Tom Barter)
6. 12:58 PM - Re: Transponder antenna ground plane (user9253)
7. 01:44 PM - Re: Transponder antenna ground plane (Peter Pengilly)
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| Subject: | Transponder antenna ground plane |
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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| Subject: | Re: Transponder antenna ground plane |
5.3" in diameter per:
http://www.matronics.com/forums/viewtopic.php?t=16762861
Round or octagon should not matter.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506531#506531
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| Subject: | Re: Transponder antenna ground plane |
At 10:48 AM 4/11/2022, you wrote:
>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?"
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| Subject: | Re: Transponder antenna ground plane |
On 4/11/2022 11:14 AM, Robert L. Nuckolls, III wrote:
> At 10:48 AM 4/11/2022, you wrote:
>
>> 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.
>> snip
>
> 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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| Subject: | 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
<mailto:kesleyelectric@iowatelecom.net> kesleyelectric@iowatelecom.net
From: owner-aeroelectric-list-server@matronics.com
<owner-aeroelectric-list-server@matronics.com> On Behalf Of Robert L.
Nuckolls, III
Sent: Monday, April 11, 2022 11:15 AM
Subject: Re: AeroElectric-List: Transponder antenna ground plane
At 10:48 AM 4/11/2022, you wrote:
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?"
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| Subject: | Re: Transponder antenna ground plane |
The ground plane probably should be grounded to the fuselage for lightning
protection. But I don't think it matters for performance.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=506535#506535
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| Subject: | Transponder antenna ground plane |
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@matronics.com
<owner-aeroelectric-list-server@matronics.com> On Behalf Of Tom Barter
Sent: 11 April 2022 19:57
Subject: RE: AeroElectric-List: 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
<mailto:kesleyelectric@iowatelecom.net> kesleyelectric@iowatelecom.net
From: owner-aeroelectric-list-server@matronics.com
<mailto:owner-aeroelectric-list-server@matronics.com>
<owner-aeroelectric-list-server@matronics.com
<mailto:owner-aeroelectric-list-server@matronics.com> > On Behalf Of Robert
L. Nuckolls, III
Sent: Monday, April 11, 2022 11:15 AM
Subject: Re: AeroElectric-List: Transponder antenna ground plane
At 10:48 AM 4/11/2022, you wrote:
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?"
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