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Deems Davis

Joined: 09 Jan 2006
Posts: 925

Posted: Sun Sep 16, 2007 9:24 am Post subject: Fiberglass and antenna placement

John W. Cox wrote:



.  Fiberglass is not transparent

to RF it creates a false positive and measurable signal loss.  It is

only translucent with a clearly diminished performance. It also requires

your output amp to work significantly harder leading to earlier

potential failure and often a loss of valuable communication when you

need it most - rain fade, cloud obscuration and turbulence



John, can you elaborate or point me to a reference source. I have always 

heard that fiberglass is transparent wrt antennas. If there is a loss 

due to the fiberglass how big of a loss is it? and what is a 'false 

positive'?  Does the fiberglass affect all spectrums equally? Both of 

the antennas in my case are receive only and are satellite based systems.



Deems Davis # 406

'Its all done....Its just not put together'

http://deemsrv10.com/

 	  Quote:

n8vim(at)arrl.net
Guest

Posted: Sun Sep 16, 2007 10:25 am Post subject: Fiberglass and antenna placement

I am an extra-class ham radio operator, so here's my opinion:



Most fiberglass is relatively transparent to RF. Glass cloth and epoxy 

don't attenuate RF much more than dust. If you put in carbon fiber, or 

other additives then the situation changes.



The biggest issues typically are actually getting 1) a good ground 

plane, and 2) good seperation from nearby antennas and other parallel 

pieces of metal which can cause an impedance mismatch.



I have several antennas on top of my tower which are actually *encased* 

in fiberglass.



Want a cheap tool for analyzing your antenna installation? Here's what I 

use (a bit overkill for the aviation band):

http://www.mfjenterprises.com/products.php?prodid=MFJ-269



-Jim 40384



Deems Davis wrote:



 	  Quote: 	
		   

 John W. Cox wrote:



 .  Fiberglass is not transparent

 to RF it creates a false positive and measurable signal loss.  It is

 only translucent with a clearly diminished performance. It also requires

 your output amp to work significantly harder leading to earlier

 potential failure and often a loss of valuable communication when you

 need it most - rain fade, cloud obscuration and turbulence



 John, can you elaborate or point me to a reference source. I have 

 always heard that fiberglass is transparent wrt antennas. If there is 

 a loss due to the fiberglass how big of a loss is it? and what is a 

 'false positive'?  Does the fiberglass affect all spectrums equally? 

 Both of the antennas in my case are receive only and are satellite 

 based systems.



 Deems Davis # 406

 'Its all done....Its just not put together'

 http://deemsrv10.com/



>

Deems Davis

Joined: 09 Jan 2006
Posts: 925

Posted: Sun Sep 16, 2007 10:49 am Post subject: Fiberglass and antenna placement

James, Thanks for the feedback, Here's another naive question: In your 

opinion would the heat which exists in the engine compartment adversely 

affect the performance of these satellited antennas?



Deems Davis # 406

'Its all done....Its just not put together'

http://deemsrv10.com/



James Hein wrote:

 	  Quote: 	
		   



 I am an extra-class ham radio operator, so here's my opinion:



 Most fiberglass is relatively transparent to RF. Glass cloth and epoxy 

 don't attenuate RF much more than dust. If you put in carbon fiber, or 

 other additives then the situation changes.



 The biggest issues typically are actually getting 1) a good ground 

 plane, and 2) good seperation from nearby antennas and other parallel 

 pieces of metal which can cause an impedance mismatch.



 I have several antennas on top of my tower which are actually 

 *encased* in fiberglass.



 Want a cheap tool for analyzing your antenna installation? Here's what 

 I use (a bit overkill for the aviation band):

 http://www.mfjenterprises.com/products.php?prodid=MFJ-269



 -Jim 40384



 Deems Davis wrote:



> 

> John W. Cox wrote:

>

> .  Fiberglass is not transparent

> to RF it creates a false positive and measurable signal loss.  It is

> only translucent with a clearly diminished performance. It also requires

> your output amp to work significantly harder leading to earlier

> potential failure and often a loss of valuable communication when you

> need it most - rain fade, cloud obscuration and turbulence

>

> John, can you elaborate or point me to a reference source. I have 

> always heard that fiberglass is transparent wrt antennas. If there is 

> a loss due to the fiberglass how big of a loss is it? and what is a 

> 'false positive'?  Does the fiberglass affect all spectrums equally? 

> Both of the antennas in my case are receive only and are satellite 

> based systems.

>

> Deems Davis # 406

> 'Its all done....Its just not put together'

> http://deemsrv10.com/

>

>>   

>

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Sun Sep 16, 2007 11:08 am Post subject: Fiberglass and antenna placement

I've always taken antenna reception quality as THE #1 reason to choose

an antenna or mounting location....especially important if you're

shooting for the same quality as a "certified" installation.  I never

understood why as experimental builders, who build planes that we pride

as being built "better than factory", anyone would build absolutely

sub-standard to all of the advice by manufacturers regarding their

installation requirements....on purpose, no less.  The fact that someone

would bother to hem and haw about a WAAS GPS antenna no less, really

makes me wonder, as the amount of drag off a small wart of an antenna

is way less than if you were talking about a Nav or Com antenna, and the

signal you're trying to receive is EXTREMELY faint in comparison.



Here's something I dug up recently:

http://www.homelandsecurity.org/bulletin/Dual%20Benefit/warner_gps_spoofing.html



"The GPS signal strength measured at the surface of the Earth is about 

–160dBw (1 x 10–16 watts), which is roughly equivalent to viewing a 

25-watt light bulb from a distance of 10,000 miles. This weak signal can 

easily be blocked by destroying or shielding the GPS receiver’s antenna. 

The GPS signal can also be effectively jammed by a signal of a similar 

frequency but greater strength. "



So then think about the many electrical noise causing things in an

airplane....probably one of the loudest of which would be the spark

plugs and ignition system.  And then to choose to actually mount

the antennas CLOSER to those items?  I mean, I've seen TV's get

scrambled signals when a snowmobile drove by the house years

ago....not that the plane is going to be as poor, but we're

*really* talking some tiny electrical signals with GPS...and sorry, but

if someone even thinks they're going to pass by on flying ILS and VOR

approaches and instead favor trusting a WAAS approach, why sacrifice?

If they're going to sacrifice that, then why bother to look at the

actual LPV-spec GPS units in the first place....just fly them with

an autopilot or EFIS driven by a 396.  (and no, I'm not REALLY

endorsing that thinking)

http://www.nap.edu/html/embedded_everywhere/ch2_b8.html

"What makes GPS reception difficult is that radio frequency (RF) signals 

from the satellites are very weak. Special coding is used to allow 

receivers to detect these weak signals, but even with coding, GPS 

receivers generally work only if they have a direct line of sight to the 

satellites. Performance inside buildings or in an area covered by 

foliage is generally quite poor"



http://www.wowinfo.com/gps/gps/chapter2n3.htm

"This is an extremely low-powered system—so low-powered, in fact, that 

the signal is really buried in the natural background radio noise. The 

receiver recovers this weak signal from the satellites by using 

spread-spectrum communication technology, a very tricky concept in 

communication theory that works by means of pseudo-random codes."



http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf

"You’d think that with all of these radio waves raining down on us from 

dozens of satellites in space

we’d all glow in the dark. Actually, the strength of the GPS signal is 

very small, equivalent to the tail

light of a car seen from 2,500 kilometers away-halfway across the U.S.! 

Weaker, in fact, than the

ordinary background radio noise that’s all around us all of the time."

So then thinking about laying it underneath fiberglass, my thought is:

"Well, if fiberglass is transparent to GPS, then how many layers are

transparent to the GPS.  Can you put it under 1/16", 1/8", 1", 5"?

At what point do you decide you've hidden the GPS from it enough?"



And, if it's under a cowl, or at some other point not mounted

horizontally with a full view of the sky in all directions, then

which of the available satellites that are now unavailable are you

happy to just toss aside from shadowing due to poor mounting?  So

some of them aren't worth seeing.



I understand the love of building a cosmetically pleasing airplane, but

to sacrifice life-saving avionics signals really makes me wonder.  And

nothing against Dan Checkoway, but it's amazing how one person's good

experience with a poor mounting choice can spread to such a universal

acceptance of the idea.  It might be better to bounce mounting

and location questions off the antenna makers and companies like Garmin

and see how far they're willing to stick their neck out with an answer.

If it were harmless, they'd have no reason to avoid giving the advice.

I've had many phone calls to Comant and questions to other antenna

makers throughout the build, which in the end mostly just led me to

try to be as "conventional" as possible to attempt the same

reliability as the certified planes could have.



Now, if someone was building a VFR only airplane, I'd say "heck yeah,

may as well give it a try".

Tim Olson - RV-10 N104CD - Flying



Deems Davis wrote:

 	  Quote: 	
		   

 

 

 John W. Cox wrote:

 

 .  Fiberglass is not transparent

 to RF it creates a false positive and measurable signal loss.  It is

 only translucent with a clearly diminished performance. It also requires

 your output amp to work significantly harder leading to earlier

 potential failure and often a loss of valuable communication when you

 need it most - rain fade, cloud obscuration and turbulence

 

 John, can you elaborate or point me to a reference source. I have always 

 heard that fiberglass is transparent wrt antennas. If there is a loss 

 due to the fiberglass how big of a loss is it? and what is a 'false 

 positive'?  Does the fiberglass affect all spectrums equally? Both of 

 the antennas in my case are receive only and are satellite based systems.

 

 Deems Davis # 406

 'Its all done....Its just not put together'

 http://deemsrv10.com/

>

n8vim(at)arrl.net
Guest

Posted: Sun Sep 16, 2007 11:16 am Post subject: Fiberglass and antenna placement

The heat in the engine compartment would affect the antennas somewhat.

Why?

1. Matching components (if used - capacitors and/or inductors) values 

will change with regard to temperature

2. Coax dielectric will soften, allowing the center conductor to migrate 

closer to the shield over time, changing the impedance of the coax, 

reducing performance.



In reality, #1 probably doesn't amount to much difference at all due to 

the small values involved, but #2 needs to be protected against (heat 

shield, etc.)



-Jim 40384



Deems Davis wrote:



 	  Quote: 	
		   



 James, Thanks for the feedback, Here's another naive question: In your 

 opinion would the heat which exists in the engine compartment 

 adversely affect the performance of these satellited antennas?



 Deems Davis # 406

 'Its all done....Its just not put together'

 http://deemsrv10.com/



 James Hein wrote:



> 

>

> I am an extra-class ham radio operator, so here's my opinion:

>

> Most fiberglass is relatively transparent to RF. Glass cloth and 

> epoxy don't attenuate RF much more than dust. If you put in carbon 

> fiber, or other additives then the situation changes.

>

> The biggest issues typically are actually getting 1) a good ground 

> plane, and 2) good seperation from nearby antennas and other parallel 

> pieces of metal which can cause an impedance mismatch.

>

> I have several antennas on top of my tower which are actually 

> *encased* in fiberglass.

>

> Want a cheap tool for analyzing your antenna installation? Here's 

> what I use (a bit overkill for the aviation band):

> http://www.mfjenterprises.com/products.php?prodid=MFJ-269

>

> -Jim 40384

>

> Deems Davis wrote:

>

>> 

>>

>>

>> John W. Cox wrote:

>>

>> .  Fiberglass is not transparent

>> to RF it creates a false positive and measurable signal loss.  It is

>> only translucent with a clearly diminished performance. It also 

>> requires

>> your output amp to work significantly harder leading to earlier

>> potential failure and often a loss of valuable communication when you

>> need it most - rain fade, cloud obscuration and turbulence

>>

>> John, can you elaborate or point me to a reference source. I have 

>> always heard that fiberglass is transparent wrt antennas. If there 

>> is a loss due to the fiberglass how big of a loss is it? and what is 

>> a 'false positive'?  Does the fiberglass affect all spectrums 

>> equally? Both of the antennas in my case are receive only and are 

>> satellite based systems.

>>

>> Deems Davis # 406

>> 'Its all done....Its just not put together'

>> http://deemsrv10.com/

>>

>>>   

>>

>>

>>

>>

>>

>>

>>

>>

>

Deems Davis

Joined: 09 Jan 2006
Posts: 925

Posted: Sun Sep 16, 2007 2:47 pm Post subject: Fiberglass and antenna placement

OK Tim, I get it, GPS signals are weak. But the question as to how much 

attenuation is attributable to the Fiberglass is not addressed anywhere 

in your clips, and still remains. The specified/recommended Commant 

Antenna for the HeadsUP XM Weather receiver (used in Avidyne 

installations in certified Cirrus 's) comes configured with a gain of 

30-34 db. The receiver itself is preset to expect a gain of 22db 

(+/-2db). The installation manual actually _recommends/requires_ some 

additional attenuation and provides a formula for figuring the amount 

available through several different  types and lengths (feet & yards) of 

coax. Turns out that you need quite a bit of coax to get  it down to the 

22db range  (17-58 ' depending on type of coax) Alternatively you may 

use a DC bias passing attenuator in line with the cable itself. (my 

choice). The only caution from the mfg about placement was to keep it 

away from transmitting antennas, (min 36's").



If, as James suggests, the fiberglass (1/16 - 3/32") of the cowl is not 

an issue in signal loss, and there are no other blocking restrictions, 

then why criticize someone who wants to make the installation 

cosmetically attractive as well? the vast majority of the 396/496 

Garmins w/ weather are flying with glareshield mounted antennas with the 

same issues.



Deems Davis # 406

'Its all done....Its just not put together'

http://deemsrv10.com/



Tim Olson wrote:

 	  Quote: 	
		   



 I've always taken antenna reception quality as THE #1 reason to choose

 an antenna or mounting location....especially important if you're

 shooting for the same quality as a "certified" installation.  I never

 understood why as experimental builders, who build planes that we pride

 as being built "better than factory", anyone would build absolutely

 sub-standard to all of the advice by manufacturers regarding their

 installation requirements....on purpose, no less.  The fact that someone

 would bother to hem and haw about a WAAS GPS antenna no less, really

 makes me wonder, as the amount of drag off a small wart of an antenna

 is way less than if you were talking about a Nav or Com antenna, and the

 signal you're trying to receive is EXTREMELY faint in comparison.



 Here's something I dug up recently:

 http://www.homelandsecurity.org/bulletin/Dual%20Benefit/warner_gps_spoofing.html 

 "The GPS signal strength measured at the surface of the Earth is about 

 –160dBw (1 x 10–16 watts), which is roughly equivalent to viewing a 

 25-watt light bulb from a distance of 10,000 miles. This weak signal 

 can easily be blocked by destroying or shielding the GPS receiver’s 

 antenna. The GPS signal can also be effectively jammed by a signal of 

 a similar frequency but greater strength. "



 So then think about the many electrical noise causing things in an

 airplane....probably one of the loudest of which would be the spark

 plugs and ignition system.  And then to choose to actually mount

 the antennas CLOSER to those items?  I mean, I've seen TV's get

 scrambled signals when a snowmobile drove by the house years

 ago....not that the plane is going to be as poor, but we're

 *really* talking some tiny electrical signals with GPS...and sorry, but

 if someone even thinks they're going to pass by on flying ILS and VOR

 approaches and instead favor trusting a WAAS approach, why sacrifice?

 If they're going to sacrifice that, then why bother to look at the

 actual LPV-spec GPS units in the first place....just fly them with

 an autopilot or EFIS driven by a 396.  (and no, I'm not REALLY

 endorsing that thinking)

 http://www.nap.edu/html/embedded_everywhere/ch2_b8.html

 "What makes GPS reception difficult is that radio frequency (RF) 

 signals from the satellites are very weak. Special coding is used to 

 allow receivers to detect these weak signals, but even with coding, 

 GPS receivers generally work only if they have a direct line of sight 

 to the satellites. Performance inside buildings or in an area covered 

 by foliage is generally quite poor"



 http://www.wowinfo.com/gps/gps/chapter2n3.htm

 "This is an extremely low-powered system—so low-powered, in fact, that 

 the signal is really buried in the natural background radio noise. The 

 receiver recovers this weak signal from the satellites by using 

 spread-spectrum communication technology, a very tricky concept in 

 communication theory that works by means of pseudo-random codes."



 http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf

 "You’d think that with all of these radio waves raining down on us 

 from dozens of satellites in space

 we’d all glow in the dark. Actually, the strength of the GPS signal is 

 very small, equivalent to the tail

 light of a car seen from 2,500 kilometers away-halfway across the 

 U.S.! Weaker, in fact, than the

 ordinary background radio noise that’s all around us all of the time."

 So then thinking about laying it underneath fiberglass, my thought is:

 "Well, if fiberglass is transparent to GPS, then how many layers are

 transparent to the GPS.  Can you put it under 1/16", 1/8", 1", 5"?

 At what point do you decide you've hidden the GPS from it enough?"



 And, if it's under a cowl, or at some other point not mounted

 horizontally with a full view of the sky in all directions, then

 which of the available satellites that are now unavailable are you

 happy to just toss aside from shadowing due to poor mounting?  So

 some of them aren't worth seeing.



 I understand the love of building a cosmetically pleasing airplane, but

 to sacrifice life-saving avionics signals really makes me wonder.  And

 nothing against Dan Checkoway, but it's amazing how one person's good

 experience with a poor mounting choice can spread to such a universal

 acceptance of the idea.  It might be better to bounce mounting

 and location questions off the antenna makers and companies like Garmin

 and see how far they're willing to stick their neck out with an answer.

 If it were harmless, they'd have no reason to avoid giving the advice.

 I've had many phone calls to Comant and questions to other antenna

 makers throughout the build, which in the end mostly just led me to

 try to be as "conventional" as possible to attempt the same

 reliability as the certified planes could have.



 Now, if someone was building a VFR only airplane, I'd say "heck yeah,

 may as well give it a try".

 Tim Olson - RV-10 N104CD - Flying



 Deems Davis wrote:

> 

> John W. Cox wrote:

>

> .  Fiberglass is not transparent

> to RF it creates a false positive and measurable signal loss.  It is

> only translucent with a clearly diminished performance. It also requires

> your output amp to work significantly harder leading to earlier

> potential failure and often a loss of valuable communication when you

> need it most - rain fade, cloud obscuration and turbulence

>

> John, can you elaborate or point me to a reference source. I have 

> always heard that fiberglass is transparent wrt antennas. If there is 

> a loss due to the fiberglass how big of a loss is it? and what is a 

> 'false positive'?  Does the fiberglass affect all spectrums equally? 

> Both of the antennas in my case are receive only and are satellite 

> based systems.

>

> Deems Davis # 406

> 'Its all done....Its just not put together'

> http://deemsrv10.com/

>>

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Sun Sep 16, 2007 3:11 pm Post subject: Fiberglass and antenna placement

Well, I don't know that you're going to find some place to get

a specific factor of attenuation from having a specified layer of

fiberglass.  I was just sorting out some antenna boxes in prep

for sending back my piece of crap Comant 401-620 though, and

read through some install docs where they actually specify things

like installation of the antenna near the leading edge of high-wing

wings, so that during climb they aren't shaded by the wing,

and they specify to mount it where things like the propeller

arc aren't in the way of the antenna's forward and upward view

too.  It would seem that during climb, a firewall mounted antenna

could be shaded quite a bit by the engine, and your comments

don't address at all the factors of electrical noise of the

ignition system.  It's all just food for thought, since a builder

can do whatever they want.



The sad part is, when looks become more important than function,

it can just lead to someone remarking later after they hear the

bad news "Gosh, and that was such a beautiful plane, too."



The 396/496 w/weather and glareshield mounted antenna's don't even

begin to approach the suitability of a WAAS approved GPS antenna

for flying approaches.  Consider that the update rate for doing the

calculations is so much higher, that the receiver really needs to

make sure it has a good incoming data stream, whereas a lesser

performing GPS may get by with more sporadic signals.



Regarding the attenuation, keep in mind that the attenuation in

the cable is going to happen AFTER the active antenna has done

it's notch filtering to reduce the external noise and non-on-freq

"stuff" coming down the pipe.



Oh, and, if the GPS signal quality weren't an issue, why would

Xbow make such noise about how they really want to see people use

some specific models of antenna, mounted in some good locations,

using proper techniques.  Seems we have actual known experiences

with their AHRS driving EFIS's screwy from lower-quality GPS

signalling.



It really doesn't matter personally to me how someone does it, as long

as they've thought it through and made an informed choice.  Just try

to put yourself into the future though, and say 50 hours into it

you start noticing the GPS just isn't what it should be....how much

harder will it be to RE-mount that stuff in a different location?

If it's no fun now, it's really gonna suck later.



Tim Olson - RV-10 N104CD - Flying

do not archive

Deems Davis wrote:

 	  Quote: 	
		   

 

 OK Tim, I get it, GPS signals are weak. But the question as to how much 

 attenuation is attributable to the Fiberglass is not addressed anywhere 

 in your clips, and still remains. The specified/recommended Commant 

 Antenna for the HeadsUP XM Weather receiver (used in Avidyne 

 installations in certified Cirrus 's) comes configured with a gain of 

 30-34 db. The receiver itself is preset to expect a gain of 22db 

 (+/-2db). The installation manual actually _recommends/requires_ some 

 additional attenuation and provides a formula for figuring the amount 

 available through several different  types and lengths (feet & yards) of 

 coax. Turns out that you need quite a bit of coax to get  it down to the 

 22db range  (17-58 ' depending on type of coax) Alternatively you may 

 use a DC bias passing attenuator in line with the cable itself. (my 

 choice). The only caution from the mfg about placement was to keep it 

 away from transmitting antennas, (min 36's").

 

 If, as James suggests, the fiberglass (1/16 - 3/32") of the cowl is not 

 an issue in signal loss, and there are no other blocking restrictions, 

 then why criticize someone who wants to make the installation 

 cosmetically attractive as well? the vast majority of the 396/496 

 Garmins w/ weather are flying with glareshield mounted antennas with the 

 same issues.

 

 Deems Davis # 406

 'Its all done....Its just not put together'

 http://deemsrv10.com/

 

 Tim Olson wrote:

> 

>

> I've always taken antenna reception quality as THE #1 reason to choose

> an antenna or mounting location....especially important if you're

> shooting for the same quality as a "certified" installation.  I never

> understood why as experimental builders, who build planes that we pride

> as being built "better than factory", anyone would build absolutely

> sub-standard to all of the advice by manufacturers regarding their

> installation requirements....on purpose, no less.  The fact that someone

> would bother to hem and haw about a WAAS GPS antenna no less, really

> makes me wonder, as the amount of drag off a small wart of an antenna

> is way less than if you were talking about a Nav or Com antenna, and the

> signal you're trying to receive is EXTREMELY faint in comparison.

>

> Here's something I dug up recently:

> http://www.homelandsecurity.org/bulletin/Dual%20Benefit/warner_gps_spoofing.html 

> "The GPS signal strength measured at the surface of the Earth is about 

> –160dBw (1 x 10–16 watts), which is roughly equivalent to viewing a 

> 25-watt light bulb from a distance of 10,000 miles. This weak signal 

> can easily be blocked by destroying or shielding the GPS receiver’s 

> antenna. The GPS signal can also be effectively jammed by a signal of 

> a similar frequency but greater strength. "

>

> So then think about the many electrical noise causing things in an

> airplane....probably one of the loudest of which would be the spark

> plugs and ignition system.  And then to choose to actually mount

> the antennas CLOSER to those items?  I mean, I've seen TV's get

> scrambled signals when a snowmobile drove by the house years

> ago....not that the plane is going to be as poor, but we're

> *really* talking some tiny electrical signals with GPS...and sorry, but

> if someone even thinks they're going to pass by on flying ILS and VOR

> approaches and instead favor trusting a WAAS approach, why sacrifice?

> If they're going to sacrifice that, then why bother to look at the

> actual LPV-spec GPS units in the first place....just fly them with

> an autopilot or EFIS driven by a 396.  (and no, I'm not REALLY

> endorsing that thinking)

> http://www.nap.edu/html/embedded_everywhere/ch2_b8.html

> "What makes GPS reception difficult is that radio frequency (RF) 

> signals from the satellites are very weak. Special coding is used to 

> allow receivers to detect these weak signals, but even with coding, 

> GPS receivers generally work only if they have a direct line of sight 

> to the satellites. Performance inside buildings or in an area covered 

> by foliage is generally quite poor"

>

> http://www.wowinfo.com/gps/gps/chapter2n3.htm

> "This is an extremely low-powered system—so low-powered, in fact, that 

> the signal is really buried in the natural background radio noise. The 

> receiver recovers this weak signal from the satellites by using 

> spread-spectrum communication technology, a very tricky concept in 

> communication theory that works by means of pseudo-random codes."

>

> http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf

> "You’d think that with all of these radio waves raining down on us 

> from dozens of satellites in space

> we’d all glow in the dark. Actually, the strength of the GPS signal is 

> very small, equivalent to the tail

> light of a car seen from 2,500 kilometers away-halfway across the 

> U.S.! Weaker, in fact, than the

> ordinary background radio noise that’s all around us all of the time."

> So then thinking about laying it underneath fiberglass, my thought is:

> "Well, if fiberglass is transparent to GPS, then how many layers are

> transparent to the GPS.  Can you put it under 1/16", 1/8", 1", 5"?

> At what point do you decide you've hidden the GPS from it enough?"

>

> And, if it's under a cowl, or at some other point not mounted

> horizontally with a full view of the sky in all directions, then

> which of the available satellites that are now unavailable are you

> happy to just toss aside from shadowing due to poor mounting?  So

> some of them aren't worth seeing.

>

> I understand the love of building a cosmetically pleasing airplane, but

> to sacrifice life-saving avionics signals really makes me wonder.  And

> nothing against Dan Checkoway, but it's amazing how one person's good

> experience with a poor mounting choice can spread to such a universal

> acceptance of the idea.  It might be better to bounce mounting

> and location questions off the antenna makers and companies like Garmin

> and see how far they're willing to stick their neck out with an answer.

> If it were harmless, they'd have no reason to avoid giving the advice.

> I've had many phone calls to Comant and questions to other antenna

> makers throughout the build, which in the end mostly just led me to

> try to be as "conventional" as possible to attempt the same

> reliability as the certified planes could have.

>

> Now, if someone was building a VFR only airplane, I'd say "heck yeah,

> may as well give it a try".

> Tim Olson - RV-10 N104CD - Flying

>

> Deems Davis wrote:

>> 

>>

>>

>> John W. Cox wrote:

>>

>> .  Fiberglass is not transparent

>> to RF it creates a false positive and measurable signal loss.  It is

>> only translucent with a clearly diminished performance. It also requires

>> your output amp to work significantly harder leading to earlier

>> potential failure and often a loss of valuable communication when you

>> need it most - rain fade, cloud obscuration and turbulence

>>

>> John, can you elaborate or point me to a reference source. I have 

>> always heard that fiberglass is transparent wrt antennas. If there is 

>> a loss due to the fiberglass how big of a loss is it? and what is a 

>> 'false positive'?  Does the fiberglass affect all spectrums equally? 

>> Both of the antennas in my case are receive only and are satellite 

>> based systems.

>>

>> Deems Davis # 406

>> 'Its all done....Its just not put together'

>> http://deemsrv10.com/

>>>

apilot2(at)gmail.com
Guest

Posted: Sun Sep 16, 2007 3:46 pm Post subject: Fiberglass and antenna placement

Well, I don't know about any of this. I use a little bluetooth GPS that I

toss on the passenger seat. Sometimes I forget and lay my aluminum lapboard

on top of it. Oh, and I have an aluminum roof with steel chrome moly tubing

supporting it. But, I consistently see, 8-9 satellites, no problem. Works

the same laying it on the console in my car. The current generation GPS

chips are truly amazing..oh, and it cost me less than $100 and it feeds my

Anywhere Map just fine. No, nothing certified...but it sure makes my

performance using those antique tools like VOR and NDB look good.   And

center didn't ask any questions how my /U airplane was going IFR direct

between 2 VORs 200nm apart.



On 9/16/07, Tim Olson <Tim(at)myrv10.com> wrote:

[quote]

 



 Well, I don't know that you're going to find some place to get

 a specific factor of attenuation from having a specified layer of

 fiberglass.  I was just sorting out some antenna boxes in prep

 for sending back my piece of crap Comant 401-620 though, and

 read through some install docs where they actually specify things

 like installation of the antenna near the leading edge of high-wing

 wings, so that during climb they aren't shaded by the wing,

 and they specify to mount it where things like the propeller

 arc aren't in the way of the antenna's forward and upward view

 too.  It would seem that during climb, a firewall mounted antenna

 could be shaded quite a bit by the engine, and your comments

 don't address at all the factors of electrical noise of the

 ignition system.  It's all just food for thought, since a builder

 can do whatever they want.



 The sad part is, when looks become more important than function,

 it can just lead to someone remarking later after they hear the

 bad news "Gosh, and that was such a beautiful plane, too."



 The 396/496 w/weather and glareshield mounted antenna's don't even

 begin to approach the suitability of a WAAS approved GPS antenna

 for flying approaches.  Consider that the update rate for doing the

 calculations is so much higher, that the receiver really needs to

 make sure it has a good incoming data stream, whereas a lesser

 performing GPS may get by with more sporadic signals.



 Regarding the attenuation, keep in mind that the attenuation in

 the cable is going to happen AFTER the active antenna has done

 it's notch filtering to reduce the external noise and non-on-freq

 "stuff" coming down the pipe.



 Oh, and, if the GPS signal quality weren't an issue, why would

 Xbow make such noise about how they really want to see people use

 some specific models of antenna, mounted in some good locations,

 using proper techniques.  Seems we have actual known experiences

 with their AHRS driving EFIS's screwy from lower-quality GPS

 signalling.



 It really doesn't matter personally to me how someone does it, as long

 as they've thought it through and made an informed choice.  Just try

 to put yourself into the future though, and say 50 hours into it

 you start noticing the GPS just isn't what it should be....how much

 harder will it be to RE-mount that stuff in a different location?

 If it's no fun now, it's really gonna suck later.



 Tim Olson - RV-10 N104CD - Flying

 do not archive

 Deems Davis wrote:

 > 

 >

 > OK Tim, I get it, GPS signals are weak. But the question as to how much

 > attenuation is attributable to the Fiberglass is not addressed anywhere

 > in your clips, and still remains. The specified/recommended Commant

 > Antenna for the HeadsUP XM Weather receiver (used in Avidyne

 > installations in certified Cirrus 's) comes configured with a gain of

 > 30-34 db. The receiver itself is preset to expect a gain of 22db

 > (+/-2db). The installation manual actually _recommends/requires_ some

 > additional attenuation and provides a formula for figuring the amount

 > available through several different  types and lengths (feet & yards) of

 > coax. Turns out that you need quite a bit of coax to get  it down to the

 > 22db range  (17-58 ' depending on type of coax) Alternatively you may

 > use a DC bias passing attenuator in line with the cable itself. (my

 > choice). The only caution from the mfg about placement was to keep it

 > away from transmitting antennas, (min 36's").

 >

 > If, as James suggests, the fiberglass (1/16 - 3/32") of the cowl is not

 > an issue in signal loss, and there are no other blocking restrictions,

 > then why criticize someone who wants to make the installation

 > cosmetically attractive as well? the vast majority of the 396/496

 > Garmins w/ weather are flying with glareshield mounted antennas with the

 > same issues.

 >

 > Deems Davis # 406

 > 'Its all done....Its just not put together'

 > http://deemsrv10.com/

 >

 > Tim Olson wrote:

 >> 

 >>

 >> I've always taken antenna reception quality as THE #1 reason to choose

 >> an antenna or mounting location....especially important if you're

 >> shooting for the same quality as a "certified" installation.  I never

 >> understood why as experimental builders, who build planes that we pride

 >> as being built "better than factory", anyone would build absolutely

 >> sub-standard to all of the advice by manufacturers regarding their

 >> installation requirements....on purpose, no less.  The fact that

 someone

 >> would bother to hem and haw about a WAAS GPS antenna no less, really

 >> makes me wonder, as the amount of drag off a small wart of an antenna

 >> is way less than if you were talking about a Nav or Com antenna, and

 the

 >> signal you're trying to receive is EXTREMELY faint in comparison.

 >>

 >> Here's something I dug up recently:

 >>

 http://www.homelandsecurity.org/bulletin/Dual%20Benefit/warner_gps_spoofing.html

 >>

 >>

 >> "The GPS signal strength measured at the surface of the Earth is about

 >> –160dBw (1 x 10–16 watts), which is roughly equivalent to viewing a

 >> 25-watt light bulb from a distance of 10,000 miles. This weak signal

 >> can easily be blocked by destroying or shielding the GPS receiver's

 >> antenna. The GPS signal can also be effectively jammed by a signal of

 >> a similar frequency but greater strength. "

 >>

 >> So then think about the many electrical noise causing things in an

 >> airplane....probably one of the loudest of which would be the spark

 >> plugs and ignition system.  And then to choose to actually mount

 >> the antennas CLOSER to those items?  I mean, I've seen TV's get

 >> scrambled signals when a snowmobile drove by the house years

 >> ago....not that the plane is going to be as poor, but we're

 >> *really* talking some tiny electrical signals with GPS...and sorry, but

 >> if someone even thinks they're going to pass by on flying ILS and VOR

 >> approaches and instead favor trusting a WAAS approach, why sacrifice?

 >> If they're going to sacrifice that, then why bother to look at the

 >> actual LPV-spec GPS units in the first place....just fly them with

 >> an autopilot or EFIS driven by a 396.  (and no, I'm not REALLY

 >> endorsing that thinking)

 >>

 >>

 >> http://www.nap.edu/html/embedded_everywhere/ch2_b8.html

 >> "What makes GPS reception difficult is that radio frequency (RF)

 >> signals from the satellites are very weak. Special coding is used to

 >> allow receivers to detect these weak signals, but even with coding,

 >> GPS receivers generally work only if they have a direct line of sight

 >> to the satellites. Performance inside buildings or in an area covered

 >> by foliage is generally quite poor"

 >>

 >> http://www.wowinfo.com/gps/gps/chapter2n3.htm

 >> "This is an extremely low-powered system—so low-powered, in fact, that

 >> the signal is really buried in the natural background radio noise. The

 >> receiver recovers this weak signal from the satellites by using

 >> spread-spectrum communication technology, a very tricky concept in

 >> communication theory that works by means of pseudo-random codes."

 >>

 >> http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf

 >> "You'd think that with all of these radio waves raining down on us

 >> from dozens of satellites in space

 >> we'd all glow in the dark. Actually, the strength of the GPS signal is

 >> very small, equivalent to the tail

 >> light of a car seen from 2,500 kilometers away-halfway across the

 >> U.S.! Weaker, in fact, than the

 >> ordinary background radio noise that's all around us all of the time."

 >>

 >>

 >> So then thinking about laying it underneath fiberglass, my thought is:

 >> "Well, if fiberglass is transparent to GPS, then how many layers are

 >> transparent to the GPS.  Can you put it under 1/16", 1/8", 1", 5"?

 >> At what point do you decide you've hidden the GPS from it enough?"

 >>

 >> And, if it's under a cowl, or at some other point not mounted

 >> horizontally with a full view of the sky in all directions, then

 >> which of the available satellites that are now unavailable are you

 >> happy to just toss aside from shadowing due to poor mounting?  So

 >> some of them aren't worth seeing.

 >>

 >> I understand the love of building a cosmetically pleasing airplane, but

 >> to sacrifice life-saving avionics signals really makes me wonder.  And

 >> nothing against Dan Checkoway, but it's amazing how one person's good

 >> experience with a poor mounting choice can spread to such a universal

 >> acceptance of the idea.  It might be better to bounce mounting

 >> and location questions off the antenna makers and companies like Garmin

 >> and see how far they're willing to stick their neck out with an answer

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Sun Sep 16, 2007 4:36 pm Post subject: Fiberglass and antenna placement

Yep, I have a bluetooth GPS on the glareshield that I use with the

tablet PC.  You're right, the technology has sure gotten good

on the radios.  But, my arguments are only for dealing with

the actual approach certified type stuff like a 430W/530W/480/Freeflight

and that sort of GPS antenna.  If someone wants to have lesser quality

weather reception, or try something with their secondary GPS,

I think that's just fine.  It's when you want to have the utmost

reliability on your primary navigation equipment that I think it's

prudent to not try to cut any corners and just follow the manufacturers

directions.  Your primary nav GPS failing is one of those

experiences that when it happens it would forcibly make you work

really hard to get things back together again to continue the

flight.



Tim Olson - RV-10 N104CD - Flying

do not archive

Kelly McMullen wrote:

 	  Quote: 	
		   Well, I don't know about any of this. I use a little bluetooth GPS that 

 I toss on the passenger seat. Sometimes I forget and lay my aluminum 

 lapboard on top of it. Oh, and I have an aluminum roof with steel chrome 

 moly tubing supporting it. But, I consistently see, 8-9 satellites, no 

 problem. Works the same laying it on the console in my car. The current 

 generation GPS chips are truly amazing..oh, and it cost me less than 

 $100 and it feeds my Anywhere Map just fine. No, nothing certified...but 

 it sure makes my performance using those antique tools like VOR and NDB 

 look good.   And center didn't ask any questions how my /U airplane 

 was going IFR direct between 2 VORs 200nm apart.

 

 On 9/16/07, *Tim Olson* <Tim(at)myrv10.com <mailto:Tim(at)myrv10.com>> wrote:

 

     

     <mailto:Tim(at)MyRV10.com>>

 

     Well, I don't know that you're going to find some place to get

     a specific factor of attenuation from having a specified layer of

     fiberglass.  I was just sorting out some antenna boxes in prep

     for sending back my piece of crap Comant 401-620 though, and

     read through some install docs where they actually specify things

     like installation of the antenna near the leading edge of high-wing

     wings, so that during climb they aren't shaded by the wing,

     and they specify to mount it where things like the propeller

     arc aren't in the way of the antenna's forward and upward view

     too.  It would seem that during climb, a firewall mounted antenna

     could be shaded quite a bit by the engine, and your comments

     don't address at all the factors of electrical noise of the

     ignition system.  It's all just food for thought, since a builder

     can do whatever they want.

 

     The sad part is, when looks become more important than function,

     it can just lead to someone remarking later after they hear the

     bad news "Gosh, and that was such a beautiful plane, too."

 

     The 396/496 w/weather and glareshield mounted antenna's don't even

     begin to approach the suitability of a WAAS approved GPS antenna

     for flying approaches.  Consider that the update rate for doing the

     calculations is so much higher, that the receiver really needs to

     make sure it has a good incoming data stream, whereas a lesser

     performing GPS may get by with more sporadic signals.

 

     Regarding the attenuation, keep in mind that the attenuation in

     the cable is going to happen AFTER the active antenna has done

     it's notch filtering to reduce the external noise and non-on-freq

     "stuff" coming down the pipe.

 

     Oh, and, if the GPS signal quality weren't an issue, why would

     Xbow make such noise about how they really want to see people use

     some specific models of antenna, mounted in some good locations,

     using proper techniques.  Seems we have actual known experiences

     with their AHRS driving EFIS's screwy from lower-quality GPS

     signalling.

 

     It really doesn't matter personally to me how someone does it, as long

     as they've thought it through and made an informed choice.  Just try

     to put yourself into the future though, and say 50 hours into it

     you start noticing the GPS just isn't what it should be....how much

     harder will it be to RE-mount that stuff in a different location?

     If it's no fun now, it's really gonna suck later.

 

     Tim Olson - RV-10 N104CD - Flying

     do not archive

 

 

     Deems Davis wrote:

      > 

     <mailto:deemsdavis(at)cox.net>>

      >

      > OK Tim, I get it, GPS signals are weak. But the question as to

     how much

      > attenuation is attributable to the Fiberglass is not addressed

     anywhere

      > in your clips, and still remains. The specified/recommended Commant

      > Antenna for the HeadsUP XM Weather receiver (used in Avidyne

      > installations in certified Cirrus 's) comes configured with a

     gain of

      > 30-34 db. The receiver itself is preset to expect a gain of 22db

      > (+/-2db). The installation manual actually _recommends/requires_ some

      > additional attenuation and provides a formula for figuring the

     amount

      > available through several different  types and lengths (feet &

     yards) of

      > coax. Turns out that you need quite a bit of coax to get  it down

     to the

      > 22db range  (17-58 ' depending on type of coax) Alternatively you

     may

      > use a DC bias passing attenuator in line with the cable itself. (my

      > choice). The only caution from the mfg about placement was to keep it

      > away from transmitting antennas, (min 36's").

      >

      > If, as James suggests, the fiberglass (1/16 - 3/32") of the cowl

     is not

      > an issue in signal loss, and there are no other blocking

     restrictions,

      > then why criticize someone who wants to make the installation

      > cosmetically attractive as well? the vast majority of the 396/496

      > Garmins w/ weather are flying with glareshield mounted antennas

     with the

      > same issues.

      >

      > Deems Davis # 406

      > 'Its all done....Its just not put together'

      > http://deemsrv10.com/

      >

      > Tim Olson wrote:

      >> 

     <mailto:Tim(at)MyRV10.com>>

      >>

      >> I've always taken antenna reception quality as THE #1 reason to

     choose

      >> an antenna or mounting location....especially important if you're

      >> shooting for the same quality as a "certified" installation.  I

     never

      >> understood why as experimental builders, who build planes that

     we pride

      >> as being built "better than factory", anyone would build absolutely

      >> sub-standard to all of the advice by manufacturers regarding their

      >> installation requirements....on purpose, no less.  The fact that

     someone

      >> would bother to hem and haw about a WAAS GPS antenna no less, really

      >> makes me wonder, as the amount of drag off a small wart of an

     antenna

      >> is way less than if you were talking about a Nav or Com antenna,

     and the

      >> signal you're trying to receive is EXTREMELY faint in comparison.

      >>

      >> Here's something I dug up recently:

      >>

     http://www.homelandsecurity.org/bulletin/Dual%20Benefit/warner_gps_spoofing.html

      >>

      >>

      >> "The GPS signal strength measured at the surface of the Earth is

     about

      >> –160dBw (1 x 10–16 watts), which is roughly equivalent to viewing a

      >> 25-watt light bulb from a distance of 10,000 miles. This weak signal

      >> can easily be blocked by destroying or shielding the GPS receiver's

      >> antenna. The GPS signal can also be effectively jammed by a

     signal of

      >> a similar frequency but greater strength. "

      >>

      >> So then think about the many electrical noise causing things in an

      >> airplane....probably one of the loudest of which would be the spark

      >> plugs and ignition system.  And then to choose to actually mount

      >> the antennas CLOSER to those items?  I mean, I've seen TV's get

      >> scrambled signals when a snowmobile drove by the house years

      >> ago....not that the plane is going to be as poor, but we're

      >> *really* talking some tiny electrical signals with GPS...and

     sorry, but

      >> if someone even thinks they're going to pass by on flying ILS

     and VOR

      >> approaches and instead favor trusting a WAAS approach, why

     sacrifice?

      >> If they're going to sacrifice that, then why bother to look at the

      >> actual LPV-spec GPS units in the first place....just fly them with

      >> an autopilot or EFIS driven by a 396.  (and no, I'm not REALLY

      >> endorsing that thinking)

      >>

      >>

      >> http://www.nap.edu/html/embedded_everywhere/ch2_b8.html

      >> "What makes GPS reception difficult is that radio frequency (RF)

      >> signals from the satellites are very weak. Special coding is

     used to

      >> allow receivers to detect these weak signals, but even with coding,

      >> GPS receivers generally work only if they have a direct line of

     sight

      >> to the satellites. Performance inside buildings or in an area

     covered

      >> by foliage is generally quite poor"

      >>

      >> http://www.wowinfo.com/gps/gps/chapter2n3.htm

      >> "This is an extremely low-powered system—so low-powered, in

     fact, that

      >> the signal is really buried in the natural background radio

     noise. The

      >> receiver recovers this weak signal from the satellites by using

      >> spread-spectrum communication technology, a very tricky concept in

      >> communication theory that works by means of pseudo-random codes."

      >>

      >> http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf

     <http://www.dot.nd.gov/manuals/surveymanual/gps-operations.pdf>

      >> "You'd think that with all of these radio waves raining down on us

      >> from dozens of satellites in space

      >> we'd all glow in the dark. Actually, the strength of the GPS

     signal is

      >> very small, equivalent to the tail

      >> light of a car seen from 2,500 kilometers away-halfway across the

      >> U.S.! Weaker, in fact, than the

      >> ordinary background radio noise that's all around us all of the

     time."

      >>

      >>

      >> So then thinking about laying it underneath fiberglass, my

     thought is:

      >> "Well, if fiberglass is transparent to GPS, then how many layers are

      >> transparent to the GPS.  Can you put it under 1/16", 1/8", 1", 5"?

      >> At what point do you decide you've hidden the GPS from it enough?"

      >>

      >> And, if it's under a cowl, or at some other point not mounted

      >> horizontally with a full view of the sky in all directions, then

      >> which of the available satellites that are now unavailable are you

      >> happy to just toss aside from shadowing due to poor mounting?  So

      >> some of them aren't worth seeing.

      >>

      >> I understand the love of building a cosmetically pleasing

     airplane, but

      >> to sacrifice life-saving avionics signals really makes me

     wonder.  And

      >> nothing against Dan Checkoway, but it's amazing how one person's

     good

      >> experience with a poor mounting choice can spread to such a

     universal

      >> acceptance of the idea.  It might be better to bounce mounting

      >> and location questions off the antenna makers and companies like

     Garmin

      >> and see how far they're willing to stick their neck out with an

     answer.

      >> If it were harmless, they'd have no reason to avoid giving the

     advice.

      >> I've had many phone calls to Comant and questions to other antenna

      >> makers throughout the build, which in the end mostly just led me to

      >> try to be as "conventional" as possible to attempt the same

      >> reliability as the certified planes could have.

      >>

      >> Now, if someone was building a VFR only airplane, I'd say "heck

     yeah,

      >> may as well give it a try".

      >>

      >>

      >> Tim Olson - RV-10 N104CD - Flying

      >>

      >>

      >>

      >> Deems Davis wrote:

      >>> 

     <deemsdavis(at)cox.net <mailto:deemsdavis(at)cox.net>>

      >>>

      >>>

      >>> John W. Cox wrote:

      >>>

      >>> .  Fiberglass is not transparent

      >>> to RF it creates a false positive and measurable signal

     loss.  It is

      >>> only translucent with a clearly diminished performance. It also

     requires

      >>> your output amp to work significantly harder leading to earlier

      >>> potential failure and often a loss of valuable communication

     when you

      >>> need it most - rain fade, cloud obscuration and turbulence

      >>>

      >>> John, can you elaborate or point me to a reference source. I have

      >>> always heard that fiberglass is transparent wrt antennas. If

     there is

      >>> a loss due to the fiberglass how big of a loss is it? and what

     is a

      >>> 'false positive'?  Does the fiberglass affect all spectrums

     equally?

      >>> Both of the antennas in my case are receive only and are satellite

      >>> based systems.

      >>>

      >>> Deems Davis # 406

      >>> 'Its all done....Its just not put together'

      >>> http://deemsrv10.com/

      >>>>

      >>

      >>

      >>

      >>

      >>

      >>

      >

      >

      >

     &gtsp;       - The RV10-List Email Forum - content now also

     available via the Web Forums! =====================

 

 

 

 

 *

 

 

 *

AV8ORJWC

Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"

Posted: Sun Sep 16, 2007 4:40 pm Post subject: Fiberglass and antenna placement

Now you guys are getting with the program.  Coax length, inline

connectors, combiners, splitters and fiberglas thickness equate to db

signal losses.



John #600



--

Deems Davis

Joined: 09 Jan 2006
Posts: 925

Posted: Sun Sep 16, 2007 4:54 pm Post subject: Fiberglass and antenna placement

OK, I just redesigned my antenna installation : atop a 5 foot tall 

pylon, made of spaceage transpardium mounted in the exact center/top 

point of the cabin cover, equipped with a gyro stabilized gimble that 

ensures stability of the antenna in all unusual attitudes.



I'm out of here



John W. Cox wrote:

[quote] 



 Now you guys are getting with the program.  Coax length, inline

 connectors, combiners, splitters and fiberglas thickness equate to db

 signal losses.



 John #600



 --

ricksked(at)embarqmail.co
Guest

Posted: Sun Sep 16, 2007 5:37 pm Post subject: Fiberglass and antenna placement

That was my reason for using the location I picked for my GPS antenna. Although I really like the under the cowl stuff, I also have a 480 and I didn't want any sacrifice in it's GPS capability by degradading the antenna performance even the slightest. I'm not sure if it WOULD under the cowl but I was pretty sure it WOULD NOT mounted on top of the fuselage.



Rick S.

40185

---

dc71(at)netspace.net.au
Guest

Posted: Sun Sep 16, 2007 6:10 pm Post subject: Fiberglass and antenna placement

After a real world test of holding a handheld GPS under the

On 17/09/2007, at 6:47 AM, Deems Davis wrote:



 	  Quote: 	
		   



 OK Tim, I get it, GPS signals are weak. But the question as to how  

 much attenuation is attributable to the Fiberglass is not addressed  

 anywhere in your clips, and still remains.


	




 	  Quote: 	
		  >> John W. Cox wrote:

>>

>> .  Fiberglass is not transparent

>> to RF it creates a false positive and measurable signal loss.  It is

>> only translucent with a clearly diminished performance.

dc71(at)netspace.net.au
Guest

Posted: Sun Sep 16, 2007 6:12 pm Post subject: Fiberglass and antenna placement

After a real world test of holding a handheld GPS under the cabin top  

then the cowl while watching the Satellite signal strength page, I'm  

convinced that there is some attenuation from fibreglass - whether  

it's significant or not is up to the individual builder. Personally I  

have installed my antennae outside the cabin top.

Indran

On 17/09/2007, at 6:47 AM, Deems Davis wrote:

 	  Quote: 	

 OK Tim, I get it, GPS signals are weak. But the question as to how  

 much attenuation is attributable to the Fiberglass is not addressed  

 anywhere in your clips, and still remains.

 	  Quote: 	
		  >> John W. Cox wrote:

>>

>> .  Fiberglass is not transparent

>> to RF it creates a false positive and measurable signal loss.  It is

>> only translucent with a clearly diminished performance.

>>

poneill(at)irealms.com
Guest

Posted: Sun Sep 16, 2007 9:02 pm Post subject: Fiberglass and antenna placement

This comes as a huge relief.  I thought I was the only one planning to equip

their RV-10 with AWACS.



Patrick

#40715





--

rvbuilder(at)sausen.net
Guest

Posted: Mon Sep 17, 2007 6:46 am Post subject: Fiberglass and antenna placement

Deems, make sure you rip all the fiberglass and plastic covering off those certified antennas too.  I think the most useful tip I have got out of this string so far is don't by anything from Commant except for maybe VHF and Transponder.  Not a surprise as when I have asked them questions in OSH they basically gave me a hand out, promptly ignored me, and walked away when they had no one else at their booth.



  Part of the reason that people are seeing better reception from the Bluetooth "bugs" is because they are using much newer technologies than the "certified" antennas.  Does that surprise anyone that the certified vendors are probably not really doing anything to improve the antennas because of the hassle to get them recertified.  Anyone else remember the horrors stories of the older certified units giving the RAIM messages, usually at the worse possible times?



  At this point I will probably have no less than 3-4 satellite antennas performing various functions.  Some will be under the canopy and some may not.  Depends on how well they function and how important they are.  Will I stick an antenna for a Garmin x96 on the outside?  Not a chance.  But for primary navigation WAAS GPS, potentially.  But only after I test it out.



  So while everyone is super concerned about if the 1/4" of fiberglass is attenuating the GPS signal in the UHF L Band microwave range (in which most outdoor antennas are protected by fiberglass or ABS plastic), has anyone actually looked at exactly how far they are running those antenna leads?  Depending on the cable type you can probably figure a loss of 0.5db for every meter of cable.  Or how about if your Bluetooth, cell phone, oscillation of that laptop clock, or RF noise from your various "uncertified" personal electronics are causing any interference in your nav systems that could induce an error?  So who wants to volunteer to do a SNR study for GPS locations on the RV-10 along with the factory coverings of said antennas?



  Just for the record I have a pair of Commant CI-121 Comm antennas, a pair of archer wingtip antennas for nav, and a Commant CI-105 transponder antenna.



Michael



--

AV8ORJWC

Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"

Posted: Mon Sep 17, 2007 2:17 pm Post subject: Fiberglass and antenna placement

Don't forget the five degree forward cant to compensate for your

additional forward airspeed with the BPE Cold Air/Davis Induction

System.



Thanks for playing.



John



--

ricksked(at)embarqmail.co
Guest

Posted: Mon Sep 17, 2007 3:15 pm Post subject: Fiberglass and antenna placement

And the drag coefficent associated with the forward cant must also be considered as well as gyroscopic precession due to the drag in the gimble, unless your going with magnetic suspension of the ring then your precession may not be significant given the fuel onboard and the total time from alignemnt to shut down after stopping to pee. lol....



Rick S.

40185

please do not archive

---

rvbuilder(at)sausen.net
Guest

Posted: Tue Sep 18, 2007 7:01 am Post subject: Fiberglass and antenna placement

You also need to figure out how to design a mechanism that will keep the lowest drag profile aligned with the relative wind.



I'm still trying to work out how to form a singularity to power an inertial dampener and gravity drive.  Then I can bolt a snow plow to the front if I want and pull 50G's.  Heh.



Do not archive



--

n8vim(at)arrl.net
Guest

Posted: Tue Sep 18, 2007 9:38 am Post subject: Fiberglass and antenna placement

I think my antennas might cause a bit too much drag:

 

 [img]cid:part1.00020908.02090002(at)arrl.net[/img]

 

 The vertical antenna on the top is a tri-band 2m, 6m, and 70cm and encased in fiberglass (15ft. tall); The main antenna is a log periodic 13-33MHz - As for scale, the boom length is just over 30 feet, longest element is 32 feet.

 

 The plane? Oh yeah.... I should get back to that.... 

 

 -Jim 40384 do not archive.

 

 RV Builder (Michael Sausen) wrote: [quote]   [quote]--> RV10-List message posted by: "RV Builder (Michael Sausen)" <rvbuilder(at)sausen.net> (rvbuilder(at)sausen.net)  You also need to figure out how to design a mechanism that will keep the lowest drag profile aligned with the relative wind.  I'm still trying to work out how to form a singularity to power an inertial dampener and gravity drive.  Then I can bolt a snow plow to the front if I want and pull 50G's.  Heh.  Do not archive  --

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