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IFR GPS Antenna Mounting Question

 
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tgesele(at)optonline.net
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PostPosted: Fri Feb 24, 2006 7:10 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Does anyone know if it is legal to mount a GPS antenna under a painted
fiberglass surface if the plane is to be flown IFR?

I'm considering mounting it on top of the vetical stab, under the fiberglass
fairing and want to find out if it's a legal location.

Thanks,
Tom Gesele #473


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rvbuilder(at)sausen.net
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PostPosted: Fri Feb 24, 2006 7:37 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I could be wrong but I don't believe there are any IFR requirements around where to mount any antennas in an experimental aircraft.  Usually antenna mounting locations are dictated by the manufacturer or basic guidelines.  Many people mount the GPS antennas under the cowl and even more mount their Nav antennas in wingtips.  As long as you have reliable reception I wouldn't worry about it.

Michael Sausen
-10 #352 Fuselage
Do not archive

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jesse(at)itecusa.org
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PostPosted: Fri Feb 24, 2006 7:39 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I can't answer technically, but from all I have read on this forum, in
experimental aircraft, this is a very big gray area even as far as flying
an experimental IFR. FYI, we have ours on the glare shield under the
windscreen and, although I am told that is not acceptable for certified
ifr flight, it should be fine for us. The main problem with putting it
back there is the amount of loss you will have in that distance of coax.
Our coax is about a foot long.

Jesse

Quote:


Does anyone know if it is legal to mount a GPS antenna under a painted
fiberglass surface if the plane is to be flown IFR?

I'm considering mounting it on top of the vetical stab, under the
fiberglass
fairing and want to find out if it's a legal location.

Thanks,
Tom Gesele #473




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pilotdds(at)aol.com
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PostPosted: Fri Feb 24, 2006 9:33 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

The problem you will have is the lenth of the coax.Accordding to Bob Archer gps reception is affected significantlly by long ant wire runs. I mounted mine on the glare shield.Works great 
 
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jwadejr(at)direcway.com
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PostPosted: Fri Feb 24, 2006 10:25 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I plan to mount mine under the cowl on the firewall. Many have mounted there with no problems. Wood or fiberglass does not affect signal strength. I should not make any difference on IFR. I mounted one under the wood structured roof of a Howard I restored, and it was legal IFR.
Jim 383
 
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lammers.david(at)mcleodus
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PostPosted: Fri Feb 24, 2006 10:56 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Tom,

To be "legal" and use a GPS in the National Airspace (NAS) system under
IFR (even in experimental airplanes) the following apply:
1) The equipment must be TSO'd. for it's intended purpose (enroute,
approach, etc)
2) To keep the TSO valid, the equipment must be installed in accordance
with the manufacturer's installation instructions/requirements.
and 3) the installed system must be tested per the manufacturer's post
installation test procedure/requirements. ( you should document this in
your flight test documentation)

So how does this apply to your question?

A) If your equipment manufacturer has specific instructions on antenna
location then you must follow them.
B) If not, you are free to mount the antenna wherever you please but you
must test to, and pass, and record or document that you passed the
system tests.

Soooooooo--mount it under your (non-metallic) painted fiberglass
surface. If you pass the test--great--if not have another location in
your "hip pocket" and move the antenna.

PS: My Garmin antenna clearly says "do not paint" on it.

Dave Lammers
RV-6 flying
RV-10 tailcone

Tom Gesele wrote:

Quote:


Does anyone know if it is legal to mount a GPS antenna under a painted
fiberglass surface if the plane is to be flown IFR?

I'm considering mounting it on top of the vetical stab, under the fiberglass
fairing and want to find out if it's a legal location.

Thanks,
Tom Gesele #473






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wcurtis(at)core.com
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PostPosted: Fri Feb 24, 2006 12:20 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

[quote]FYI, we have ours on the glare shield under the windscreen and, >although I am told that is not acceptable for certified ifr >flight, it should be fine for us. Next time someone says some crap like this, just ask them to cite the reference in FAR Part 23. I bet he won't find it. The antenna placement and specification is usually in the TSO for the GPS by the manufacturer and looking at the Garmin installation manual, any permanent location with full view of the sky and adequate ground plane would do. Not sure what GPS is used, but the nice think about Garmin GPS antennas is that they are powered --even the portable ones! But for the panel mount units, I think when Garmin designed these things, they had cabin class turboprops in mind, which is why they originally came out only with 28 volt versions. I'm sure you could have some awful long antenna coax cable runs in a King Air as you look for an available spot outside the pressure vessel. So the VS tip should be fine -even with the long (as far as RV standards) coax cable run. Not sure where I'll put mine. Was thinking about just rear of the fiberglass cabin top or under the cowling. William Curtis http://nerv10.com/

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jesse(at)itecusa.org
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PostPosted: Fri Feb 24, 2006 2:58 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I am sorry I offended you with my "crap". What I meant was (and notice my
comment about not having the technical answer) that in certified aircraft
they may have specific requirements for antenna placement, but he
regulations seem to be less strict for experimental. Let me rephrase with
more technical language...I have heard from a reliable source that the
Garmin installation manual says that any permanent location with full view
of the sky and adequate ground plane would do, of which the glare shield
should be fine for us. Thanks for calling me on that one. It's been a
long day with the computer crash and everything.

by all means, do not archive

Jesse

Quote:
>FYI, we have ours on the glare shield under the windscreen and,
>although I am told that is not acceptable for certified ifr
>flight, it should be fine for us.

Next time someone says some crap like this, just ask them to cite the
reference in FAR Part 23. I bet he won't find it.

The antenna placement and specification is usually in the TSO for the GPS
by the manufacturer and looking at the Garmin installation manual, any
permanent location with full view of the sky and adequate ground plane
would do. Not sure what GPS is used, but the nice think about Garmin GPS
antennas is that they are powered --even the portable ones! But for the
panel mount units, I think when Garmin designed these things, they had
cabin class turboprops in mind, which is why they originally came out only
with 28 volt versions. I'm sure you could have some awful long antenna
coax cable runs in a King Air as you look for an available spot outside
the pressure vessel. So the VS tip should be fine -even with the long (as
far as RV standards) coax cable run.

Not sure where I'll put mine. Was thinking about just rear of the
fiberglass cabin top or under the cowling.
William Curtis
http://nerv10.com/


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acs(at)acspropeller.com.a
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PostPosted: Fri Feb 24, 2006 3:23 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Jesse, and everyone else by all means keep the so called "crap" coming. This
is how we learn. After all it's a discussion forum. You take what you want
from the info supplied.
John 40315 Fuse
do not archive

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wcurtis(at)core.com
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PostPosted: Sat Feb 25, 2006 6:00 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

[quote]I am sorry I offended you with my "crap". Jesse, This was not directed at you, more to the person that told you it was not acceptable without citing the reference. In all my years of airplane ownership, unfortunately it has become my standard response because some many people seem to make up FARs on the fly. No offence intended, no offence felt. Do not archive. William Curtis http://nerv10.com/

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tgesele(at)optonline.net
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PostPosted: Sat Feb 25, 2006 6:54 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

As a follow-up, I sent the same inquiry to the manufacturer of the GPS I
plan on using, here's the response:

"So long as the antenna has a clear line of sight to the sky and is not
compromised by either the fuselage or the paint then it should be okay. I'd
strongly recommend that you test it in the desired position before making a
final commitment however. WAAS receivers are much more sensitive to
multi-path reflected signals and you may find that it has to be installed
outside on top."

Based on that, I'll likely be mounting the GPS antenna on top of the
fuselage someplace.

Thanks to all who replied..

Tom Gesele #473

Quote:


Does anyone know if it is legal to mount a GPS antenna under a painted
fiberglass surface if the plane is to be flown IFR?

I'm considering mounting it on top of the vetical stab, under the
fiberglass
fairing and want to find out if it's a legal location.

Thanks,
Tom Gesele #473




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Tdawson(at)avidyne.com
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PostPosted: Sat Feb 25, 2006 10:47 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

The GPS is one of the lowest-profile antennas you are going to have, so why not install in on the outside, with lots of metal ground plane around it?

TDT
40025
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coop85(at)bellsouth.net
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PostPosted: Sun Feb 26, 2006 6:17 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I agree that the GPS antenna is so small it's hardly an issue aesthetically.
I have a question about the ground plane comment though. I have also read
on the list that the longer the coax the greater the signal loss, which is
amplified on the WAAS systems. My question is, is it better to accept the
greater loss and go with a better ground plane by installing it just aft of
the cabin, or go with min coax and put it at the front of the cabin (per Tim
Olson) but have no ground plane?

Thanks,
Marcus

Do Not Archive

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n8vim(at)arrl.net
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PostPosted: Sun Feb 26, 2006 6:34 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Marcus,
Yes, coax has losses; The higher the frequency the higher the loss.
Now, most external GPS antennas are amplified, so at the point where the
signal is received, before it gets sent down the coax, it is amplified -
thus overcoming cable losses (up to a point).

Before someone points out that GPS antennas aren't powered because there
are no power connections on the antenna.... There is a DC power signal
(usually 5v) sent on the coax. This signal doesn't cause problems
because the RF signal is decoupled by a capacitor inside the GPS.

-Jim 40384 (Also an extra class ham radio operator)

Marcus Cooper wrote:

[quote]

I agree that the GPS antenna is so small it's hardly an issue aesthetically.
I have a question about the ground plane comment though. I have also read
on the list that the longer the coax the greater the signal loss, which is
amplified on the WAAS systems. My question is, is it better to accept the
greater loss and go with a better ground plane by installing it just aft of
the cabin, or go with min coax and put it at the front of the cabin (per Tim
Olson) but have no ground plane?

Thanks,
Marcus

Do Not Archive

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Tim(at)MyRV10.com
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PostPosted: Sun Feb 26, 2006 6:39 am    Post subject: IFR GPS Antenna Mounting Question Reply with quote

I'm not sure of this other than what the Comant tech told me, but...
The GPS/WSI combo antenna I got (should also be same for plain GPS)
doesn't require a ground PLANE, but it does require a ground wire
that runs to the antenna so it has a return path for the active
powered stuff. I don't know if it would perform better with a
ground plane though. I've considered actually putting a ground
plane in, on the inside of the cabin, under the headliner.
I'd do it in a minute if it was required, but right now I'm
trying to fly and see how it goes. So far the GPS is
tracking perfectly. My TruTrak, Chelton, and GNS480 all read
the exact same heading at all times. Great stuff.

Tim Olson - RV-10 N104CD - Flying
do not archive
Marcus Cooper wrote:
[quote]

I agree that the GPS antenna is so small it's hardly an issue aesthetically.
I have a question about the ground plane comment though. I have also read
on the list that the longer the coax the greater the signal loss, which is
amplified on the WAAS systems. My question is, is it better to accept the
greater loss and go with a better ground plane by installing it just aft of
the cabin, or go with min coax and put it at the front of the cabin (per Tim
Olson) but have no ground plane?

Thanks,
Marcus

Do Not Archive

--


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Tdawson(at)avidyne.com
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PostPosted: Mon Feb 27, 2006 2:02 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Of course, Tim means track, not heading . . . : )

TDT
do not archive

________________________________

From: owner-rv10-list-server(at)matronics.com on behalf of Tim Olson
Sent: Sun 2/26/2006 9:38 AM
To: rv10-list(at)matronics.com
Subject: Re: IFR GPS Antenna Mounting Question



I'm not sure of this other than what the Comant tech told me, but...
The GPS/WSI combo antenna I got (should also be same for plain GPS)
doesn't require a ground PLANE, but it does require a ground wire
that runs to the antenna so it has a return path for the active
powered stuff. I don't know if it would perform better with a
ground plane though. I've considered actually putting a ground
plane in, on the inside of the cabin, under the headliner.
I'd do it in a minute if it was required, but right now I'm
trying to fly and see how it goes. So far the GPS is
tracking perfectly. My TruTrak, Chelton, and GNS480 all read
the exact same heading at all times. Great stuff.

Tim Olson - RV-10 N104CD - Flying
do not archive
Marcus Cooper wrote:
[quote]

I agree that the GPS antenna is so small it's hardly an issue aesthetically.
I have a question about the ground plane comment though. I have also read
on the list that the longer the coax the greater the signal loss, which is
amplified on the WAAS systems. My question is, is it better to accept the
greater loss and go with a better ground plane by installing it just aft of
the cabin, or go with min coax and put it at the front of the cabin (per Tim
Olson) but have no ground plane?

Thanks,
Marcus

Do Not Archive

--


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Tim(at)MyRV10.com
Guest





PostPosted: Mon Feb 27, 2006 2:33 pm    Post subject: IFR GPS Antenna Mounting Question Reply with quote

Ok Mr. GPS police....I concurr. Wink

Tim Olson - RV-10 N104CD - Flying
do not archive
Tim Dawson-Townsend wrote:
[quote]
Of course, Tim means track, not heading . . . : )

TDT
do not archive

________________________________

From: owner-rv10-list-server(at)matronics.com on behalf of Tim Olson
Sent: Sun 2/26/2006 9:38 AM
To: rv10-list(at)matronics.com
Subject: Re: IFR GPS Antenna Mounting Question





I'm not sure of this other than what the Comant tech told me, but...
The GPS/WSI combo antenna I got (should also be same for plain GPS)
doesn't require a ground PLANE, but it does require a ground wire
that runs to the antenna so it has a return path for the active
powered stuff. I don't know if it would perform better with a
ground plane though. I've considered actually putting a ground
plane in, on the inside of the cabin, under the headliner.
I'd do it in a minute if it was required, but right now I'm
trying to fly and see how it goes. So far the GPS is
tracking perfectly. My TruTrak, Chelton, and GNS480 all read
the exact same heading at all times. Great stuff.

Tim Olson - RV-10 N104CD - Flying
do not archive


Marcus Cooper wrote:
>
>
> I agree that the GPS antenna is so small it's hardly an issue aesthetically.
> I have a question about the ground plane comment though. I have also read
> on the list that the longer the coax the greater the signal loss, which is
> amplified on the WAAS systems. My question is, is it better to accept the
> greater loss and go with a better ground plane by installing it just aft of
> the cabin, or go with min coax and put it at the front of the cabin (per Tim
> Olson) but have no ground plane?
>
> Thanks,
> Marcus
>
> Do Not Archive
>
> --


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