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Michael Wynn
Joined: 10 Jan 2006
Posts: 148
Location: San Ramon, CA
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 Posted: Sun May 20, 2012 6:56 am Post subject: Ground plane for GPS antenna? |
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Hi all,
I am building an RV 8. Per the suggestion of several builders, I make a bracket to hold my GPS antenna under the cowl, just forward of the firewall. The bracket is bolted to the firewall. I painted it to match my engine and plenum. I got to wondering if the paint was an error. I know that the nav and com antennae don't work without connection to the ground plane of the aircraft. Is that also true for a GPS antenna? The antenna is the one that came with a Garmin 430W.
It would be easy enough to buff off the paint where the antenna rests. The bracket is pretty will grounded to the airframe by its bolts. Would that suffice for a ground plane if it is needed?
Thanks,
Michael Wynn
RV 8 Finishing
San Ramon, CA
[quote][b]
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Michael Wynn
RV 8
San Ramon, CA |
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nuckolls.bob(at)aeroelect
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| Posted: Sun May 20, 2012 7:54 am Post subject: Ground plane for GPS antenna? |
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At 09:55 AM 5/20/2012, you wrote:
| Quote: | Hi all,
I am building an RV 8. Per the suggestion of several builders, I make a bracket to hold my GPS antenna under the cowl, just forward of the firewall. The bracket is bolted to the firewall. I painted it to match my engine and plenum. I got to wondering if the paint was an error. I know that the nav and com antennae don't work without connection to the ground plane of the aircraft. Is that also true for a GPS antenna? The antenna is the one that came with a Garmin 430W.
It would be easy enough to buff off the paint where the antenna rests. The bracket is pretty will grounded to the airframe by its bolts. Would that suffice for a ground plane if it is needed?
Thanks,
Michael Wynn
RV 8 Finishing
San Ramon, CA
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GPS antennas do not generally rely on any sort of
ground plane provided by surrounding support structure.
The little flat GPS antennas are generally of the
"patch" variety. See:
http://home.iae.nl/users/plundahl/antenne/patchant.htm
So paint UNDER the antenna is of no significance. Paint
over the antenna MIGHT be significant.
Bob . . . [quote][b]
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jason(at)jasonbeaver.com
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| Posted: Sun May 20, 2012 9:08 am Post subject: Ground plane for GPS antenna? |
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The install manual for my Garmin GTN-635 specified that the antenna be grounded to the airframe and have a minimum of 7.5 radius around the perimeter. Here's an excerpt from the manual: 2.5.5 Ground Plane Ensure that the GPS/NAV/COM antennas are electrically bonded to the aircraft. Follow the aircraft manufacturers‘ instructions for the NAV and COM antenna installations, or obtain other FAA approval. The GPS/WAAS antenna requires a minimum ground plane radius of 7.5 inches around the perimeter of the antenna. Refer to Figure 2-10. For metal aircraft, the surrounding metal skin on which the antenna is mounted supplies the ground plane. For non-metal aircraft, the ground plane can be composed of heavy duty aluminum foil tape, such as 3M P/N 438 or other adhesive backed dead soft aluminum foil minimum 0.012 inches thick. It should be noted that if the antenna is struck by lightning, the foil by itself may not be sufficient to dissipate lightning currents. Additional protection may be needed depending on the construction of the structure to which the antenna is mounted. jason
On May 20, 2012 at 11:53 AM "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote: > At 09:55 AM 5/20/2012, you wrote: > >Hi all, > > > >I am building an RV 8. Per the suggestion of several builders, I > >make a bracket to hold my GPS antenna under the cowl, just forward > >of the firewall. The bracket is bolted to the firewall. I painted > >it to match my engine and plenum. I got to wondering if the paint > >was an error. I know that the nav and com antennae don't work > >without connection to the ground plane of the aircraft. Is that > >also true for a GPS antenna? The antenna is the one that came with > >a Garmin 430W. > > > >It would be easy enough to buff off the paint where the antenna > >rests. The bracket is pretty will grounded to the airframe by its > >bolts. Would that suffice for a ground plane if it is needed? > > > >Thanks, > > > >Michael Wynn > >RV 8 Finishing > >San Ramon, CA > > > > GPS antennas do not generally rely on any sort of > ground plane provided by surrounding support structure. > The little flat GPS antennas are generally of the > "patch" variety. See: > > http://home.iae.nl/users/plundahl/antenne/patchant.htm > > So paint UNDER the antenna is of no significance. Paint > over the antenna MIGHT be significant. > > Bob . . .
[quote][b]
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bobsv35b(at)aol.com
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| Posted: Sun May 20, 2012 9:22 am Post subject: Ground plane for GPS antenna? |
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Good Afternoon Jason,
I think if you read between the lines you will see that the concern is for static build up or lightning strike considerations.
The antenna will work just fine as long as it is NOT in a major shadow of a large component of the metallic airframe with no connection to the airframe at all. The bonding and grounding of the antenna, unlike a normal comm antenna, has nothing to do with it's efficiency as an antenna.
Make any sense at all?
Happy Skies,
Old Bob
Downers Grove, IL
--
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Michael Wynn
Joined: 10 Jan 2006
Posts: 148
Location: San Ramon, CA
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| Posted: Sun May 20, 2012 9:44 am Post subject: Ground plane for GPS antenna? |
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Thanks, guys. Now I can leave my nice paint job intact.
Regards,
Michael Wynn
RV 8 Finishing
San Ramon, CA
In a message dated 5/20/2012 10:22:52 A.M. Pacific Daylight Time, bobsv35b(at)aol.com writes:
| Quote: | Good Afternoon Jason,
I think if you read between the lines you will see that the concern is for static build up or lightning strike considerations.
The antenna will work just fine as long as it is NOT in a major shadow of a large component of the metallic airframe with no connection to the airframe at all. The bonding and grounding of the antenna, unlike a normal comm antenna, has nothing to do with it's efficiency as an antenna.
Make any sense at all?
Happy Skies,
Old Bob
Downers Grove, IL
-----Original Message-----
From: jason <jason(at)jasonbeaver.com>
To: aeroelectric-list <aeroelectric-list(at)matronics.com>
Sent: Sun, May 20, 2012 12:09 pm
Subject: Re: Ground plane for GPS antenna?
The install manual for my Garmin GTN-635 specified that the antenna be grounded to the airframe and have a minimum of 7.5 radius around the perimeter. Here's an excerpt from the manual:
2.5.5 Ground Plane
Ensure that the GPS/NAV/COM antennas are electrically bonded to the aircraft. Follow the aircraft manufacturers‘ instructions for the NAV and COM antenna installations, or obtain other FAA approval.
The GPS/WAAS antenna requires a minimum ground plane radius of 7.5 inches around the perimeter of the antenna. Refer to Figure 2-10. For metal aircraft, the surrounding metal skin on which the antenna is mounted supplies the ground plane. For non-metal aircraft, the ground plane can be composed of heavy duty aluminum foil tape, such as 3M P/N 438 or other adhesive backed dead soft aluminum foil minimum 0.012 inches thick. It should be noted that if the antenna is struck by lightning, the foil by itself may not be sufficient to dissipate lightning currents. Additional protection may be needed depending on the construction of the structure to which the antenna is mounted.
jason
On May 20, 2012 at 11:53 AM "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | At 09:55 AM 5/20/2012, you wrote:
>Hi all,
>
>I am building an RV 8. Per the suggestion of several builders, I
>make a bracket to hold my GPS antenna under the cowl, just forward
>of the firewall. The bracket is bolted to the firewall. I painted
>it to match my engine and plenum. I got to wondering if the paint
>was an error. I know that the nav and com antennae don't work
>without connection to the ground plane of the aircraft. Is that
>also true for a GPS antenna? The antenna is the one that came with
>a Garmin 430W.
>
>It would be easy enough to buff off the paint where the antenna
>rests. The bracket is pretty will grounded to the airframe by its
>bolts. Would that suffice for a ground plane if it is needed?
>
>Thanks,
>
>Michael Wynn
>RV 8 Finishing
>San Ramon, CA
>
GPS antennas do not generally rely on any sort of
ground plane provided by surrounding support structure.
The little flat GPS antennas are generally of the
"patch" variety. See:
http://home.iae.nl/users/plundahl/antenne/patchant.htm
So paint UNDER the antenna is of no significance. Paint
over the antenna MIGHT be significant.
Bob . . .
ist" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List
tp://forums.matronics.com
_blank">http://www.matronics.com/contribution
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[quote][b]
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Michael Wynn
RV 8
San Ramon, CA |
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jason(at)jasonbeaver.com
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| Posted: Sun May 20, 2012 9:44 am Post subject: Ground plane for GPS antenna? |
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Hi Bob,
I don't think you can infer that their concern is lightning strike protection since they specify that a foil ground plane be installed on non-metal aircraft and then go on to state that the foil may not be sufficient to dissipate lightning currents. The inference is that the ground plane is improving its efficiency as an antenna.
jason
On May 20, 2012 at 1:21 PM bobsv35b(at)aol.com wrote: > > Good Afternoon Jason, > > I think if you read between the lines you will see that the concern is for static build up or lightning strike considerations. > > The antenna will work just fine as long as it is NOT in a major shadow of a large component of the metallic airframe with no connection to the airframe at all. The bonding and grounding of the antenna, unlike a normal comm antenna, has nothing to do with it's efficiency as an antenna. > > Make any sense at all? > > Happy Skies, > > Old Bob > Downers Grove, IL > > > --
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bobsv35b(at)aol.com
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| Posted: Sun May 20, 2012 10:32 am Post subject: Ground plane for GPS antenna? |
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Good Afternoon Jason,
Since I have no idea what they were trying to handle, I cannot say that your thoughts are incorrect. However, my feeling is that the foil is an effort to better distribute static build up on the airframe.
As a WAG, I would think that having the antenna not well grounded to the airframe could mean that more corrosion could develop where the antenna meets the airframe. Still no effect on the signal until such time as the integrity of the component is compromised. Once again, that is an area in which I have NO technical knowledge.
My experience with a whole lot of different GPS antennas has been that no ground plane has any effect, positive or negative, on the performance of a GPS antenna. My knowledge of radio frequencies is nil. Just a lot of actual practical observation of results and a very small appreciation of the very short wave lengths involved.
I should also add that for lightning to actually strike an airplane is an almost implausible event. What we normally call a lightning strike is actually a massive discharge of static electricity. A whole lot of static electricity could interfere with any radio wave reception.
Happy Skies,
Old Just an Observer, not an Engineer, Bob
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Brantel
Joined: 23 Aug 2008
Posts: 53
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| Posted: Tue May 22, 2012 7:37 am Post subject: Re: Ground plane for GPS antenna? |
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The 430W antenna is an active antenna that needs ~5v phantom power that it gets from the cable/430W unit.
From a Garmin Install Manual:
* Antenna Doubler/Backing Plate
The antenna installation must provide adequate support for the antenna considering a maximum drag load
of 5 lbs. (at subsonic speed). When penetrating the skin with a large hole (i.e. for the coax connector) a
doubler plate is required to re-instate the integrity of the aircraft skin. Never weaken the aircraft structure
when choosing a mounting area. Make use of any available reinforcements where appropriate.
* Antenna Grounding Plane
Although no ground plane is required, the antennas typically perform better when a ground plane is used.
The ground plane should be a conductive surface as large as practical, with a minimum diameter of 8
inches. To use an antenna in aircraft with fabric or composite skin, a ground plane is recommended. It is
usually installed under the skin of the aircraft, below the antenna, and is made of either aluminum sheet or
of wire mesh.
* Antenna Grounding
The antenna is grounded through the mounting hardware and the coax connection. The mounting
hardware (washers and nuts) and doubler plate should make contact with an unpainted grounded surface
ensuring proper antenna grounding. It is important to have good conductivity between the coaxial shield
and the ground plane. The bottom of the antenna does not need to make contact with the ground plane
(i.e. the surface may be painted). The antenna will capacitively couple to the ground plane beneath the
paint or aircraft cover.
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