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GPS antenna

 
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harleyrider.57(at)juno.co
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PostPosted: Fri Jan 27, 2006 5:38 am    Post subject: GPS antenna Reply with quote

Hi all,
I'm building a tube & fabric airplane. I know that GPS can "see" through
fiberglass but does anyone know if it also can see through poly-fiber fabric
finished with the UV protectant silver paint on it?

Thanks,
Eric Newton - Long Beach, MS
BH #682
http://mybearhawk.com


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Dan.Beadle(at)hq.inclines
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PostPosted: Fri Jan 27, 2006 7:38 am    Post subject: GPS antenna Reply with quote

I don't know the direct answer - I suspect it would be fine.

The real simple way to find out is a test.

Take your GPS (even a hand-held will do). Select the satellite screen.
Let it lock on for a couple minutes and look at the signal strength (the
height of the bars)

Then take several layers of doped up fabric and lay over the antenna.
Wait a minute or so, then look at the signal levels. If there is little
or no change, you are in great shape. By using several layers, you
increase the attenuation effect of the fabric to simulate worst case.

Hope this helps and let us know the results

Dan
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PeterHunt1(at)AOL.COM
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PostPosted: Sat Jan 28, 2006 2:44 pm    Post subject: GPS Antenna Reply with quote

I mounted my GPS antenna under Van's fiberglass engine cowl on a little
stand attached to the engine side of the firewall. I even painted the cowl with
a metallic paint. My antenna works GREAT!

Pete in Clearwater
Garmin 530 in an all electric IFR panel
39 hours


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flyboy.bob(at)gmail.com
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PostPosted: Sat Jan 28, 2006 9:32 pm    Post subject: GPS Antenna Reply with quote

Peter,

Have you attempted to measure the "attenuation factor" if any?

I'm installing a 430 in an all electric IFR Panel in a RV-8.

Thanks,
Bob in Iowa
On 1/28/06, PeterHunt1(at)aol.com <PeterHunt1(at)aol.com> wrote:
Quote:


I mounted my GPS antenna under Van's fiberglass engine cowl on a little
stand attached to the engine side of the firewall. I even painted the cowl with
a metallic paint. My antenna works GREAT!

Pete in Clearwater
Garmin 530 in an all electric IFR panel
39 hours




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BobsV35B(at)aol.com
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PostPosted: Sun Jan 29, 2006 5:17 am    Post subject: GPS Antenna Reply with quote

Good Morning All,

Somewhere in my totally uninformed background I thought I had been told that
the GPS antenna required no ground plane at all.

I have seen them mounted on a wooden support just beneath the fabric on a
couple of Beech Staggerwings and I have seen many supported by various means
near a Plexiglas window or canopy, all without ground planes.

The question posed by Bob In Iowa adds another facet to the first questions.


Does the lack of a ground plane cause a loss in signal strength?

Does the requirement to bring the signal through Plexiglas, fiberglass or
fabric cause a loss?

If these are factors, how does one measure the loss?

Happy Skies,

Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503


In a message dated 1/28/2006 11:34:05 P.M. Central Standard Time,
flyboy.bob(at)gmail.com writes:

Peter,

Have you attempted to measure the "attenuation factor" if any?

I'm installing a 430 in an all electric IFR Panel in a RV-8.

Thanks,
Bob in Iowa


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Bruce(at)glasair.org
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PostPosted: Sun Jan 29, 2006 5:37 am    Post subject: GPS Antenna Reply with quote

My guess would be no and no. GPS is a digital signal, it's very weak and the
reciever is designed, because it knows what to look for, to pull this weak
signal from very noisy backgrounds.

Bruce
www.glasair.org


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aadamson(at)highrf.com
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PostPosted: Sun Jan 29, 2006 7:14 am    Post subject: GPS Antenna Reply with quote

Let's see if we can make sense of this.

Actually, it has nothing to do with whether it's an analog or digital
signal. Most GPS antennas are what's called "patch" antennas. This means
that there are two pieces of metal that are on different vertical planes.
These planes are actually inside the antenna housing and one is the ground
plane (in effect it's built in). Most of the aviation antennas are also
"active" antennas. This means there is a small voltage that comes from the
receiver to active components in the antenna, one of which is usually a
pre-amplifier. There are two types of amplification, one for King radios
(larger amplification needs), and one for garmin radios (smaller
amplification needs).

Because gps uses 2.4-2.5ghz, these planes of metal are only about 1" square
(yep, usually both are square) and only separated by 1/8" or so. As you
might imagine the wavelength at 2.4G is pretty short.

The most critical issue with a GPS antenna, it to make sure it has a "clear"
view of the sky. Anything that could degrade the signal, will remove some
of the quality of signal.

Alan

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Bill Denton



Joined: 10 Jan 2006
Posts: 97
Location: Chicago, IL USA

PostPosted: Sun Jan 29, 2006 7:34 am    Post subject: GPS Antenna Reply with quote

Could you clarify your use of the word "clear" in the following statement:

The most critical issue with a GPS antenna, it to make sure it has a "clear"
view of the sky.

This could be read as "with no metallic objects blocking all or part of the
view", or as "with nothing, metallic or otherwise, between the antenna and
the satellite".

You gave such an excellent explanation that I want to make sure that I've
got it 100%...

--


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aadamson(at)highrf.com
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PostPosted: Sun Jan 29, 2006 7:59 am    Post subject: GPS Antenna Reply with quote

Any "obstruction", or part of an "obstruction" will degrade the signal in
some way. Metal objects will be the worst, and even fiberglass will degrade
the signal to some extent. With fiberglass, it has to do more with
thickness. With metal, or conductive objects (like carbon fiber), it has to
do with obscuration.

It's a very small antenna (approx 1" x 1") and to gather as much signal as
possible, it needs to see as much of the sky/satellites as it can. This is
complicated somewhat by being in a aircraft to begin with. An Airplane can
"bank" and "pitch", so your view of the sky, and any obstructions, need to
take that into account. Think about it this way. If the satellite had a
string attached from it to your airplane, what parts of the plane
(obstructions) would get in the way of a "clear" view of the sky/satellite,
as the plane moves, pitches, banks, etc. This is compounded by the fact
that most GPS receivers are 12 if not 16 channel, so they are actually
seeing 12 or 16 satellites at the same time with each of the satellites
being in different sky locations...

You probably will never find the *perfect spot*, so you just need to pick
the spot with the most "clear" view of the entire sky and hopefully it will
be the spot with the least of the evils.

Hope this helps.

Alan

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flyboy.bob(at)gmail.com
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PostPosted: Sun Jan 29, 2006 8:52 am    Post subject: GPS Antenna Reply with quote

In my case anything becomes something of a compromise . . . If I put
the antenna behind the canopy, on top of the fuselage, and leave it
white (unpainted) I end up with 10 more of RG/400 which isn't
insignificant at 2.4 Ghz (but maybe not much of a factor with an
active antenna?) . . . If I put it on the glare shield and paint it
black I have Plexiglas and a layer of paint attenuating the signal, or
if as suggested put it under the cowl I have the fiberglass and paint
in the way?!

So Alan and anyone else that wishes to comment, what would you choose?

Thanks,
Bob in Iowa

On 1/29/06, Alan K. Adamson <aadamson(at)highrf.com> wrote:
[quote]

Any "obstruction", or part of an "obstruction" will degrade the signal in
some way. Metal objects will be the worst, and even fiberglass will degrade
the signal to some extent. With fiberglass, it has to do more with
thickness. With metal, or conductive objects (like carbon fiber), it has to
do with obscuration.

It's a very small antenna (approx 1" x 1") and to gather as much signal as
possible, it needs to see as much of the sky/satellites as it can. This is
complicated somewhat by being in a aircraft to begin with. An Airplane can
"bank" and "pitch", so your view of the sky, and any obstructions, need to
take that into account. Think about it this way. If the satellite had a
string attached from it to your airplane, what parts of the plane
(obstructions) would get in the way of a "clear" view of the sky/satellite,
as the plane moves, pitches, banks, etc. This is compounded by the fact
that most GPS receivers are 12 if not 16 channel, so they are actually
seeing 12 or 16 satellites at the same time with each of the satellites
being in different sky locations...

You probably will never find the *perfect spot*, so you just need to pick
the spot with the most "clear" view of the entire sky and hopefully it will
be the spot with the least of the evils.

Hope this helps.

Alan

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rv8ch



Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

PostPosted: Sun Jan 29, 2006 9:16 am    Post subject: GPS Antenna Reply with quote

Quote:
. . . If I put it on the glare shield and paint it
black I have Plexiglas and a layer of paint attenuating the signal, or
if as suggested put it under the cowl I have the fiberglass and paint
in the way?!

So Alan and anyone else that wishes to comment, what would you choose?

Any chance you can find a compatible black antenna on the
market somewhere?

--
Mickey Coggins
http://www.rv8.ch/
#82007 finishing
do not archive


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khorton01(at)rogers.com
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PostPosted: Sun Jan 29, 2006 10:02 am    Post subject: GPS Antenna Reply with quote

On 29 Jan 2006, at 10:58, Alan K. Adamson wrote:

Quote:

<aadamson(at)highrf.com>

Any "obstruction", or part of an "obstruction" will degrade the
signal in
some way. Metal objects will be the worst, and even fiberglass
will degrade
the signal to some extent. With fiberglass, it has to do more with
thickness. With metal, or conductive objects (like carbon fiber),
it has to
do with obscuration.

My GPS picks up useable signals inside my garage. The signal has to
come through the shingles, the plywood in the roof, several inches of
pink fibreglas insulation, more plywood and drywall and my plexiglas
canopy before it gets to the antenna. I'm sure the signal is
degraded, as the number of satellites seen is lower than it should
be. But it still locks on to five or six every time I fire it up.

If you want the best possible performance, then put the antenna
outside. But many people have put them under the cowl, and they
report the GPS still works fine.

Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8


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brian



Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

PostPosted: Sun Jan 29, 2006 10:51 am    Post subject: GPS Antenna Reply with quote

BobsV35B(at)aol.com wrote:

Quote:
Somewhere in my totally uninformed background I thought I had been told that
the GPS antenna required no ground plane at all.

I think it depends on the type of patch antenna used. Some have one
built-in. Some don't.

Quote:
Does the lack of a ground plane cause a loss in signal strength?

Does the requirement to bring the signal through Plexiglas, fiberglass or
fabric cause a loss?

The answer to this is 'yes' but the real question is, what are your
signal margins. The nice thing about space communications is that path
loss is relatively fixed allowing successful operation at very low
signal margins. The only real problem is rain-fade and this is usually
not a big problem at 1.7 GHz where GPS operates.

Quote:
If these are factors, how does one measure the loss?

It would be nice if the receiver actually provided the actual
single-to-noise ratio number:

E /N
b/ 0

(E sub bee over N sub zero)

but most receivers just provide a number between zero and 127 or zero
and 255.

The key is to see if your receiver locks up reliably on satellites that
are very close to the horizon. If it can see a bird that has an
elevation of only 5-10 degrees, your system is working just fine.

Remember that ANY metal between your antenna and the bird, and that
means an engine mount tube or your head, will make the signal from that
bird go away as far as the GPS receiver is concerned.

--
Brian Lloyd 361 Catterline Way
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery


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brian-yak at lloyd dot com
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nghertner(at)verizon.net
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PostPosted: Sun Jan 29, 2006 2:49 pm    Post subject: GPS Antenna Reply with quote

On 1/29/06 12:14 PM, "Mickey Coggins" <mick-matronics(at)rv8.ch> wrote:

Quote:

<mick-matronics(at)rv8.ch>

> . . . If I put it on the glare shield and paint it
> black I have Plexiglas and a layer of paint attenuating the signal, or
> if as suggested put it under the cowl I have the fiberglass and paint
> in the way?!
>
> So Alan and anyone else that wishes to comment, what would you choose?

Any chance you can find a compatible black antenna on the
market somewhere?

The Trimble antenna is black.

You guys are a lot more esoteric into this stuff than I; I called the Garmin
tech folks who told me to put their antenna under the fiberglass without a
ground plane and be done with it. No problem. Lory Ghertner


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Gilles.Thesee(at)ac-greno
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PostPosted: Sun Jan 29, 2006 3:02 pm    Post subject: GPS Antenna Reply with quote

Quote:
>>o Alan and anyone else that wishes to comment, what would you choose?
>>
>>
>Any chance you can find a compatible black antenna on the
>market somewhere?
>
>

Hi all,

Don't remember what the original poster's GPS was, but if it is the
ubiquitous Garmin 400 series, the following antenna is black,
inexpensive (24 euros with coax, yes sir), and works great.
We regularly catch satellites from inside a closed hangar. The reception
has always been flawless in flight.
See
http://contrails.free.fr/gps_en.php

FWIW,

Regards,
Gilles Thesee
Grenoble, France
http://contrails.free.fr


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Mark Sletten



Joined: 10 Jan 2006
Posts: 43
Location: St. Jacob, IL (Near St. Louis, MO)

PostPosted: Mon Jan 30, 2006 4:42 am    Post subject: GPS Antenna Reply with quote

Put it on the glare shield under whatever material (leather, cloth, etc.)
you plan to use.

Mark


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flyboy.bob(at)gmail.com
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PostPosted: Mon Jan 30, 2006 7:24 am    Post subject: GPS Antenna Reply with quote

Mark,

That may be a great idea!

Thanks,
Bob

On 1/30/06, Mark & Lisa <marknlisa(at)hometel.com> wrote:
Quote:


Put it on the glare shield under whatever material (leather, cloth, etc.)
you plan to use.

Mark




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Tim(at)MyRV10.com
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PostPosted: Mon Jan 30, 2006 10:57 am    Post subject: GPS Antenna Reply with quote

On my comant WSI/GPS antenna, they answered my question
more than once about grounds. They said it does not
require a ground plane, but it does require a ground. It needs
to have a ground on the screws at least, just to allow the
active circuitry voltages to power the thing. Other than
that, nothing.
Tim Olson -- RV-10 #40170
BobsV35B(at)aol.com wrote:
Quote:




Good Morning All,

Somewhere in my totally uninformed background I thought I had been told that
the GPS antenna required no ground plane at all.

I have seen them mounted on a wooden support just beneath the fabric on a
couple of Beech Staggerwings and I have seen many supported by various means
near a Plexiglas window or canopy, all without ground planes.

The question posed by Bob In Iowa adds another facet to the first questions.


Does the lack of a ground plane cause a loss in signal strength?

Does the requirement to bring the signal through Plexiglas, fiberglass or
fabric cause a loss?

If these are factors, how does one measure the loss?

Happy Skies,

Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Air Park LL22
Downers Grove, IL 60516
630 985-8503


In a message dated 1/28/2006 11:34:05 P.M. Central Standard Time,
flyboy.bob(at)gmail.com writes:

Peter,

Have you attempted to measure the "attenuation factor" if any?

I'm installing a 430 in an all electric IFR Panel in a RV-8.

Thanks,
Bob in Iowa



















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