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GPS antenna

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harleyrider.57(at)juno.co
Guest

Posted: Fri Jan 27, 2006 5:38 am Post subject: GPS antenna

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

Dan.Beadle(at)hq.inclines
Guest

Posted: Fri Jan 27, 2006 7:38 am Post subject: GPS antenna

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

--

PeterHunt1(at)AOL.COM
Guest

Posted: Sat Jan 28, 2006 2:44 pm Post subject: GPS Antenna

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

flyboy.bob(at)gmail.com
Guest

Posted: Sat Jan 28, 2006 9:32 pm Post subject: GPS Antenna

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

BobsV35B(at)aol.com
Guest

Posted: Sun Jan 29, 2006 5:17 am Post subject: GPS Antenna

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

Bruce(at)glasair.org
Guest

Posted: Sun Jan 29, 2006 5:37 am Post subject: GPS Antenna

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

 



--

aadamson(at)highrf.com
Guest

Posted: Sun Jan 29, 2006 7:14 am Post subject: GPS Antenna

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



--

Bill Denton

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

Posted: Sun Jan 29, 2006 7:34 am Post subject: GPS Antenna

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%...



--

aadamson(at)highrf.com
Guest

Posted: Sun Jan 29, 2006 7:59 am Post subject: GPS Antenna

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



--

flyboy.bob(at)gmail.com
Guest

Posted: Sun Jan 29, 2006 8:52 am Post subject: GPS Antenna

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



 --

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Sun Jan 29, 2006 9:16 am Post subject: GPS Antenna

 	  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

_________________
Mickey Coggins
http://www.rv8.ch/

khorton01(at)rogers.com
Guest

Posted: Sun Jan 29, 2006 10:02 am Post subject: GPS Antenna

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

brian

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

Posted: Sun Jan 29, 2006 10:51 am Post subject: GPS Antenna

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

_________________
Brian Lloyd
brian-yak at lloyd dot com
+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

nghertner(at)verizon.net
Guest

Posted: Sun Jan 29, 2006 2:49 pm Post subject: GPS Antenna

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

Gilles.Thesee(at)ac-greno
Guest

Posted: Sun Jan 29, 2006 3:02 pm Post subject: GPS Antenna

 	  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

Mark Sletten

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

Posted: Mon Jan 30, 2006 4:42 am Post subject: GPS Antenna

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

you plan to use.



Mark

_________________
Mark Sletten
Legacy FG N828LM
http://www.legacyfgbuilder.com

flyboy.bob(at)gmail.com
Guest

Posted: Mon Jan 30, 2006 7:24 am Post subject: GPS Antenna

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

Tim(at)MyRV10.com
Guest

Posted: Mon Jan 30, 2006 10:57 am Post subject: GPS Antenna

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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