Re: [time-nuts] Improving performance of a GPS antenna...?

[Peter Schmelcher]

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?


You might have been looking at a Stealth ground plane antenna.
http://facility.unavco.org/science_tech/dev_test/testing/zephyrperformance.pdf

I recall seeing a long time ago a CAD image of a ground plane disc (non 
metallic?) with lots and lots of holes. The hole to material ratio 
increased with radius I guess to match the free space impedance at the disc 
edge and eliminate diffraction.


These guys had a different idea
http://webone.novatel.ca/assets/Documents/Papers/gps_pinwheel_ant.pdf

page 19 and 20 show a gps antenna on a robotic arm getting calibrated
http://www.oregon.gov/ODOT/HWY/GEOMETRONICS/docs/presentations/1-11-12_OGUG-Improvements_NSRS.pdf?ga=t
Then of course you can also correct for the phase center variation of the 
transmitting antenna.

http://www.iapg.bv.tum.de/46790-bD1lbg-~iapg~forschung~gnss~antenna.html


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Morris Odell]

Thanks for the replies.

Yes it's definitely 5V from the receiver.

That advice re the pipe mount sounds good - that will be the next step!

Morris



--

Are you sure that the Oncore VP sends the right voltage to the antenna?  
This type needs 5 V and most pucks are designed for 3.3 V .  According 
to the manual the VP sends 5 V to the antenna but anyway it is easy to 
measure.

Regards,
Ignacio, EB4APL



The timing antenna inside the pointed radome is a helix, not a
patch antenna.
Are helix antenna designed to be used with baseplates like the pie
tin?  (I'm not sure.) The obvious experiment is to remove the plate
and mount it as it was designed to be mounted on a pole.  It is very
easy to make a proper mount for this kind of antenna, just buy 3/4
pipe flang from any hardware store and a short section of 3/4 inch
pipe.  I was lucky to find the pipe flange had holes in the correct
location but one could also mount it to the flange using velcro or
double side foam tape.



Chris Albertson
Redondo Beach, California



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Re: [time-nuts] Improving performance of a GPS antenna...?

[Chris Albertson]

On Thu, Apr 5, 2012 at 2:28 PM, EB4APL  wrote:
> Hi,
>
> Are you sure that the Oncore VP sends the right voltage to the antenna?
>  This type needs 5 V and most pucks are designed for 3.3 V .  According to
> the manual the VP sends 5 V to the antenna but anyway it is easy to measure.
>
> Regards,
> Ignacio, EB4APL
>
>
>
> On 05/04/2012 3:43, Morris Odell wrote:
>>
>> Hi all,
>>
>> While we're on this subject, I have a related question.
>>
>> I recently bought one of those cone shaped Lucent GPS timing antennas from
>> a
>> vendor in China. I'm using it for one of my GPS controlled clocks which
>> contains a 6 channel Oncore VP receiver and is on the end of about 15 feet
>> of RG58. I mounted the antenna on a small Al plate about 10 X 20 cm
>> attached
>> to a balcony rail 3 stories from the ground with a clear view of about 75%
>> of the sky.

The typical timing antenna inside the pointed radome is a helix, not a
patch antenna.
Are helix antenna designed to be used with baseplates like the pie
tin?  (I'm not sure.) The obvious experiment is to remove the plate
and mount it as it was designed to be mounted on a pole.  It is very
easy to make a proper mount for this kind of antenna, just buy 3/4
pipe flang from any hardware store and a short section of 3/4 inch
pipe.  I was lucky to find the pipe flange had holes in the correct
location but one could also mount it to the flange using velcro or
double side foam tape.



Chris Albertson
Redondo Beach, California

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Re: [time-nuts] Improving performance of a GPS antenna...?

[EB4APL]

Hi,

Are you sure that the Oncore VP sends the right voltage to the antenna?  
This type needs 5 V and most pucks are designed for 3.3 V .  According 
to the manual the VP sends 5 V to the antenna but anyway it is easy to 
measure.


Regards,
Ignacio, EB4APL



On 05/04/2012 3:43, Morris Odell wrote:

Hi all,

While we're on this subject, I have a related question.

I recently bought one of those cone shaped Lucent GPS timing antennas from a
vendor in China. I'm using it for one of my GPS controlled clocks which
contains a 6 channel Oncore VP receiver and is on the end of about 15 feet
of RG58. I mounted the antenna on a small Al plate about 10 X 20 cm attached
to a balcony rail 3 stories from the ground with a clear view of about 75%
of the sky.

I would have expected that the receiver would see quite a few satellites, a
similar arrangement with a magnetic puck antenna regularly sees up to 6
birds. The Lucent however regularly only sees one. Could this be due to the
way it's mounted?  Could the baseplate have something to do with it?

Any advice would be welcome.

Morris


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Re: [time-nuts] Improving performance of a GPS antenna...?

[michael cook]

There was some discussion on this here a while back. I had issues with bad 
reflections and wanted to know if there was a possibility of creating a 
variable mask angle. I had found a reference to a program developed by Leica to 
do just that. The links however ended in a dead end. 
It would be a nice addition to a nuts arsenal. As all sat trajectories would 
need to be know to compare against the mask it would also be possible to 
automatically program the selection of single sats for timing where the 
receiver allows.
Mike


De : Chuck Forsberg WA7KGX N2469R
Date : 5 avril 2012 14h49
À : time-nuts@febo.com
Cc : 
Objet : Re: [time-nuts] Improving performance of a GPS antenna...?

What sort of interference?? What is causing it? Any possibility of correcting 
it?I am interested in more information. Will look for whats later in the 
thread. I have a situation where there is interference coming from a specific 
direction (close to the horizon). Is it feasible to block/attenuate/absorb 
L-band signals from one direction? -- Björn 
___ time-nuts mailing list -- 
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instructions there.-- Chuck Forsberg WA7KGX N2469R c...@omen.com 
www.omen.comDeveloper of Industrial ZMODEM(Tm) for Embedded Applications Omen 
Technology Inc "The High Reliability Software"10255 NW Old Cornelius Pass 
Portland OR 97231 
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Re: [time-nuts] Improving performance of a GPS antenna...?

[Azelio Boriani]

How do you know it is coming from a specific direction? There is a
terrestrial L-band transmitter? A radio link? Try to put a screen
n*lambda+lambda/2 from the GPS antenna to create a null for the offending
L-band frequency...

On Thu, Apr 5, 2012 at 2:49 PM, Chuck Forsberg WA7KGX N2469R
wrote:

> What sort of interference??  What is causing it?  Any possibility of
> correcting it?
>
> I am interested in more information. Will look for whats later in the
> thread. I have a situation where there is interference coming from a
> specific direction (close to the horizon). Is it feasible to
> block/attenuate/absorb L-band signals from one direction? -- Björn
> ___ time-nuts mailing list --
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> instructions there.
>
> --
> Chuck Forsberg WA7KGX N2469R c...@omen.com   www.omen.com
> Developer of Industrial ZMODEM(Tm) for Embedded Applications
>  Omen Technology Inc  "The High Reliability Software"
> 10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430
>
>
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Re: [time-nuts] Improving performance of a GPS antenna...?

[Chuck Forsberg WA7KGX N2469R]

What sort of interference??  What is causing it?  Any possibility of 
correcting it?


I am interested in more information. Will look for whats later in the 
thread. I have a situation where there is interference coming from a 
specific direction (close to the horizon). Is it feasible to 
block/attenuate/absorb L-band signals from one direction? -- Björn 
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--
Chuck Forsberg WA7KGX N2469R c...@omen.com   www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
  Omen Technology Inc  "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430


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Re: [time-nuts] Improving performance of a GPS antenna...?

[bg]

Jim,

> There's a new "choke ring" style antenna (patented, of course, and they
> deserve it) which uses spikes instead of solid rings. And, they wrap the
> choke over a hemispherical surface as opposed to on a plane.
>
> Much tougher to design and fabricate  (no buying sets of cake pans any
> more), but if you want to differentiate yourself from the horde of
> Ashtech/D&M style chokes, you need something.

There are actually two new designs one coming from Novatel where the
"rings" are put in a pyramide/cone. The "rings" are also shopped of into
small ring segments.

 http://webone.novatel.ca/assets/Documents/Papers/GNSS-750.pdf

The other, coming as a response to the Novatel antenna, is from Topcon
which uses spikes.

   http://www.topconpositioning.com/products/gps/antennas/pn-a5
   http://www.topconpositioning.com/sites/default/files/PN-A5_white_paper.pdf


> At JPL, we also use what's called a "helibowl" for ground testing.  It's
> a quad helix or other element inside a bowl.  Doesn't have much pattern
> close to the horizon.  I suspect you can google and find more details,
> or if people are interested, I can ask around about design information.

I am interested in more information. Will look for whats later in the
thread. I have a situation where there is interference coming from a
specific direction (close to the horizon). Is it feasible to
block/attenuate/absorb L-band signals from one direction?

--

   Björn


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Robert Atkinson]

Hi Brooke,
RAM mat is a good idea, but I'm not sure that signal blocking is a good test, 
it could just be reflecting. A better test is to put a small piece in a 
microwave along with a cup of water (as dummy load) and see how hot it gets. 
Best done at low power and short time when household manager is not around. The 
smell if burning rubber in the microwave may not go down well.
 
Robert G8RPI.



From: Brooke Clarke 
To: Discussion of precise time and frequency measurement  
Sent: Wednesday, 4 April 2012, 21:28
Subject: Re: [time-nuts] Improving performance of a GPS antenna...?

Hi Mike:

I used military surplus radar absorbing material to stop reflections on a 
satellite antenna by applying it to the rain 
gutter, see:
http://www.prc68.com/I/Images/SB_angw.jpg

A sheet of this stuff about 4 x 6 feet weighed maybe 40 pounds.  An easy way to 
confirm it works is to use it to block a 
receiver antenna and see how far the signal goes down.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html


Michael Baker wrote:
> Hello, Time-Nutters--
>
> I saw a rather expensive GPS antenna made by one of the
> big-name GPS survey equipment mfgrs that was mounted
> on top of a 12 or 15 inch diameter disc about 3/4 inch thick.
>
> Turns out that the disc is made of some sort of RF absorbent
> foam covered by a weather-proofing coating of some sort.
>
> If one were to try to home-brew something like this, where
> would a small piece of the RF absorbent material be obtained
> without having to spend too much $$ for this experiment?
>
> Thanks for any feedback on this!!
>
> Mike Baker
> WA4HFR
> 
>
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Re: [time-nuts] Improving performance of a GPS antenna...?

[lists]

"I mounted the antenna on a small Al plate about 10 X 20 cm attached
to a balcony rail 3 stories from the ground with a clear view of about 75%
of the sky.

I would have expected that the receiver would see quite a few satellites, a
similar arrangement with a magnetic puck antenna regularly sees up to 6
birds. The Lucent however regularly only sees one. Could this be due to the
way it's mounted?  Could the baseplate have something to do with it?"

If the GPS is known to be good, I would suspect the antenna is defective. I 
wouldn't blame the ground plane. 

That said, I just wonder if you should use a ground plane for an antenna not 
designed to be used over a ground plane? Is the ground plane itself a source of 
reflection?

Incidentally, the RF absorbing part of the thread was quite interesting. 

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Re: [time-nuts] Improving performance of a GPS antenna...?

[Morris Odell]

Hi all,

While we're on this subject, I have a related question. 

I recently bought one of those cone shaped Lucent GPS timing antennas from a
vendor in China. I'm using it for one of my GPS controlled clocks which
contains a 6 channel Oncore VP receiver and is on the end of about 15 feet
of RG58. I mounted the antenna on a small Al plate about 10 X 20 cm attached
to a balcony rail 3 stories from the ground with a clear view of about 75%
of the sky.

I would have expected that the receiver would see quite a few satellites, a
similar arrangement with a magnetic puck antenna regularly sees up to 6
birds. The Lucent however regularly only sees one. Could this be due to the
way it's mounted?  Could the baseplate have something to do with it?

Any advice would be welcome.

Morris 


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Bill Hawkins]

My first job was in a blasting cap plant in 1960. Raw materials and
finished product were kept in earthen bunkers separated by a distance
that would prevent an explosion in one from propagating (the distances
were found by experience).

Tall, grounded masts were spaced among the bunkers to prevent strikes
by lightning. There is a 45 degree cone of protection from the top of
the mast to the ground. This is based on British Navy experience with
sail masts of warships between 1793 and 1847. There were 220 strikes
reported in that time. 2/3 of them struck the top masts. Only 1 in 50
struck the hull below the masts. See the report at
http://www.lightningsafety.com/nlsi_lhm/conventionalLPT.pdf
and search the PDF for "cone of protection"

Then again, this outfit says the cone is a myth
http://www.lightningsafety.com/index.html

All I know is that we never lost a bunker in the 5 years I was there.
We did have thunderstorms near Kingston, NY, 90 miles above NYC. The
safety department tested the mast grounds with an instrument like a
megger that used two probes driven in the ground (IIRC) to measure
less than a tenth of an ohm resistance to ground.

Looking back on it, I don't think anything would survive a direct hit
on the mast. It was more a matter of the mast misdirecting the leader
of the strike to look elsewhere for ground. Or, given the small numbers,
maybe it was probability that saved us, like snapping your fingers to
keep the tigers away in North America.

Lightning arrestors for lead-ins are still a very good investment.

Bill Hawkins

PS- The worst explosion I remember there was the day a new technician
took a few pounds of scrap powder to the burning grounds. It was
supposed to be mixed with ten times as much sawdust to make it burn
instead of detonate. He got the proportions backwards. The explosion
got the attention of everybody in the plant.



-Original Message-
From: Chris Albertson
Sent: Wednesday, April 04, 2012 12:53 PM

People will argue that if you ground the pole it then will become a
"lightning magnet"   That thinking is 180 degrees backward.  A pole
becomes a lightning magnet if it is allowed to charge above ground
potential.  So for most of us who don't live in Florida a #10 wire
clamped to the mast and run off to a ground rod is good enough.


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Brooke Clarke]

Hi Mike:

I used military surplus radar absorbing material to stop reflections on a satellite antenna by applying it to the rain 
gutter, see:

http://www.prc68.com/I/Images/SB_angw.jpg

A sheet of this stuff about 4 x 6 feet weighed maybe 40 pounds.  An easy way to confirm it works is to use it to block a 
receiver antenna and see how far the signal goes down.


Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html


Michael Baker wrote:

Hello, Time-Nutters--

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?

Thanks for any feedback on this!!

Mike Baker
WA4HFR


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Chris Albertson]

On Wed, Apr 4, 2012 at 10:31 AM, beale  wrote:
>>  ---Original Message---
>>  From: Chris Albertson 
>>  Better and faster way to get good performance is to buy a 10 foot section 
>> of 3/4" pipe and a pipe flange.  Place your GPS antenna on the  flange and 
>> then attach the pipe to the tallest thing around.  Then  there will be no 
>> reflectors that are above the antenna's horizon and no multi path.
>
> That should work, but if you live in thunderstorm country, making your 
> antenna the tallest thing around can come back to bite you.

people say this all the time but many ham radio operators have antenna
masts that are very tall and actually survive storms.  All TV and
radio stations do too.And then I owned a sail boat for years along
with thousands of others.   and it does not take much of a mast for
you to be the tallest thing on the water. The trick to being safe
is to make sure the antenna has a VERY low impedance path to a good
ground.  On my boat I had a 60+ foot aluminum mast that was over a
6,000 pound cast lead keel and the two where electrically connected.
 So one end of the system had a good saltwater ground.   It is hard to
do that well at home but you can come close.

People will argue that if you ground the pole it then will become a
"lightening magnet"   That thinking is 180 degrees backward.  A pole
becomes a lightening magnet if it is allowed to charge above ground
potential.  So for most of us who don't live in Florida and #10 wire
clamped to the mast and run off to a ground rod is good enough.  It is
also required by most building codes.   Even outdoor TV antenna have
the same code requirement.

One more argument:  Let's agree the a tall grounded pole is a
lightening rod.  then if the house is going to be struck would you
prefer to have the rod or not?  Without it, the lighting will find
some other patch like a furnace exhaust vent or whatever

So I guess I'd say that a GPS on a mast is not worse than any other antenna.
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [time-nuts] Improving performance of a GPS antenna...?

[beale]

>  ---Original Message---
>  From: Chris Albertson 
>  Better and faster way to get good performance is to buy a 10 foot section of 
> 3/4" pipe and a pipe flange.  Place your GPS antenna on the  flange and then 
> attach the pipe to the tallest thing around.  Then  there will be no 
> reflectors that are above the antenna's horizon and no multi path.

That should work, but if you live in thunderstorm country, making your antenna 
the tallest thing around can come back to bite you.

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Re: [time-nuts] Improving performance of a GPS antenna...?

[Chris Albertson]

Maybe get some a wide tupperware dish and fill it with water and just
a little salt.  It may not be as portable but it would turn RF into
heat well enough.   The trick is to add sale until the water will just
conduct RF so you need an RF signal generator and a pair of metal
probes and a way to measure RF current

In all cases if you build this using any material, water, foam,
conductive paint or whatever you will need to have some way to measure
its effectiveness.How to measure GPS multi path resistance?

Better and faster way to get good performance is to buy a 10 foot
section of 3/4" pipe and a pipe flange.  Place your GPS antenna on the
flange and then attach the pipe to the tallest thing around.  Then
there will be no reflectors that are above the antenna's horizon and
no multi path.

Surveyors need the special antenna because they work close to the
ground and can't choose a good antenna location.  You are not a
surveyor and can simply move the antenna.






On Wed, Apr 4, 2012 at 5:53 AM, Michael Baker  wrote:
> Hello, Time-Nutters--
>
> I saw a rather expensive GPS antenna made by one of the
> big-name GPS survey equipment mfgrs that was mounted
> on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

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Re: [time-nuts] Improving performance of a GPS antenna...?

[Jim Lux]

On 4/4/12 7:35 AM, Chuck Forsberg WA7KGX N2469R wrote:

If foliage does such a number on GPS signals, just fill a big garbage bag
with yard debris and set the antenna in the middle of that.



*wet* yard debris..


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Jim Lux]

On 4/4/12 5:53 AM, Michael Baker wrote:

Hello, Time-Nutters--

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?



This material may or may not be what you want
http://www.chomerics.com/products/CHO-MUTE.htm

Parker-Chomerics *does* do samples  (probably a 10-15cm square piece 
that is mailable)


http://www.lairdtech.com/ is another supplier

http://www.masttechnologies.com/magnetic-vs-dielectric-absorber-selection/

http://www.emc-products.dk/

http://www.arc-tech.com/

http://www.aemi-inc.com/  - pyramidal absorber
http://www.ets-lindgren.com/Absorbers

If you get the blue pyramidal absorber, get the kind that has the 
waterproof coating.. not only is it more rugged, it doesn't shed as much 
of that horrible blue/black conductive dust.  (we had a roof leak in one 
of our indoor ranges at JPL a few years ago, and wound up having to buy 
all new absorber.. turns out that the fire-proofing and conductive salts 
wash out..)



Even if you have to buy the stuff, it's not all that expensive, usually. 
 Last time (5 years ago) that I bought pyramidal absorber it was 
something like $20/2x2 foot panel.  The elastomer isn't a whole lot more 
expensive: it's made in huge quantities and the raw materials are cheap. 
 The dominant cost is the packaging/shipping & handling.


the ferrite loaded elastomer is quite dense.  It reminds me of the lead 
apron they put on you when you get dental x-rays.  It's thin and floppy, 
but surprisingly heavy.


Once you get a handle on the names and kinds of stuff you might want, 
you can probably find a way to get it.  You might find it at somewhere 
like Newark or Allied.



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Re: [time-nuts] Improving performance of a GPS antenna...?

[Chuck Forsberg WA7KGX N2469R]

If foliage does such a number on GPS signals, just fill a big garbage bag
with yard debris and set the antenna in the middle of that.

On 04/04/2012 05:53 AM, Michael Baker wrote:

Hello, Time-Nutters--

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?

Thanks for any feedback on this!!

Mike Baker
WA4HFR


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--
Chuck Forsberg WA7KGX N2469R c...@omen.com   www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
  Omen Technology Inc  "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Jim Lux]

On 4/4/12 6:56 AM, Robert Berg wrote:

You can get inexpensive conductive foam from Amazon.



Not all conductive foam works as a decent RF absorber.  If the 
conductivity isn't well matched to 377 ohms, then the RF reflects right 
off of it.  The black foam that ICs used to come in is a good example.


The sheet RF absorber (as opposed to the pyramidal kind) typically has 
multiple layers of conductive sheet separated by a fairly lossless foam, 
with the conductivities and spacing of sheets chosen to optimize the 
absorption for a particular frequency range and angle of incidence. As 
with any RF load, the important thing is the "match".


Pyramidal absorbers (like you see in an anechoic chamber) make use of 
"cones" (so there's not a real sharp "transition" in impedance), and for 
higher frequencies, the reflections head down deeper into the valleys 
between the peaks.  (at least for angles of incidence close to normal).


All of the absorbers have very different properties at grazing angles 
than they do at normal incidence.


And, what you might be seeing is actually a magnetic absorber to 
suppress creeping waves along the surface.  It's a ferrite loaded 
elastomer. We use a lot of it at work, for instance, around the outside 
of a corrugated horn to suppress back/side lobes.



There's a new "choke ring" style antenna (patented, of course, and they 
deserve it) which uses spikes instead of solid rings. And, they wrap the 
choke over a hemispherical surface as opposed to on a plane.


Much tougher to design and fabricate  (no buying sets of cake pans any 
more), but if you want to differentiate yourself from the horde of 
Ashtech/D&M style chokes, you need something.


At JPL, we also use what's called a "helibowl" for ground testing.  It's 
a quad helix or other element inside a bowl.  Doesn't have much pattern 
close to the horizon.  I suspect you can google and find more details, 
or if people are interested, I can ask around about design information.








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Re: [time-nuts] Improving performance of a GPS antenna...?

[Azelio Boriani]

So it can be done: try to emulate the Zephyr GPS antenna with the RF
absorber.

On Wed, Apr 4, 2012 at 3:56 PM, Robert Berg  wrote:

> You can get inexpensive conductive foam from Amazon.
>
>
> On 4/4/2012 5:53 AM, Michael Baker wrote:
>
>> Hello, Time-Nutters--
>>
>> I saw a rather expensive GPS antenna made by one of the
>> big-name GPS survey equipment mfgrs that was mounted
>> on top of a 12 or 15 inch diameter disc about 3/4 inch thick.
>>
>> Turns out that the disc is made of some sort of RF absorbent
>> foam covered by a weather-proofing coating of some sort.
>>
>> If one were to try to home-brew something like this, where
>> would a small piece of the RF absorbent material be obtained
>> without having to spend too much $$ for this experiment?
>>
>> Thanks for any feedback on this!!
>>
>> Mike Baker
>> WA4HFR
>> 
>>
>> __**_
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/**
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
>
> __**_
> time-nuts mailing list -- time-nuts@febo.com
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> mailman/listinfo/time-nuts
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>
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Re: [time-nuts] Improving performance of a GPS antenna...?

[Robert Berg]

You can get inexpensive conductive foam from Amazon.

On 4/4/2012 5:53 AM, Michael Baker wrote:

Hello, Time-Nutters--

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?

Thanks for any feedback on this!!

Mike Baker
WA4HFR


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Re: [time-nuts] Improving performance of a GPS antenna...?

[Joseph Gray]

You could cut up a military surplus RF blanket :-) For those who don't
know, you cover the radome of an aircraft with this when the radar is
transmitting, so you don't cook anyone nearby. I never knew how
effective it was, but I didn't walk in front of the aircraft, just to
be safe.

Joe Gray
W5JG

On Wed, Apr 4, 2012 at 6:53 AM, Michael Baker  wrote:
> Hello, Time-Nutters--
>
> I saw a rather expensive GPS antenna made by one of the
> big-name GPS survey equipment mfgrs that was mounted
> on top of a 12 or 15 inch diameter disc about 3/4 inch thick.
>
> Turns out that the disc is made of some sort of RF absorbent
> foam covered by a weather-proofing coating of some sort.
>
> If one were to try to home-brew something like this, where
> would a small piece of the RF absorbent material be obtained
> without having to spend too much $$ for this experiment?
>
> Thanks for any feedback on this!!
>
> Mike Baker
> WA4HFR
> 
>
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> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>

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[time-nuts] Improving performance of a GPS antenna...?

[Michael Baker]

Hello, Time-Nutters--

I saw a rather expensive GPS antenna made by one of the
big-name GPS survey equipment mfgrs that was mounted
on top of a 12 or 15 inch diameter disc about 3/4 inch thick.

Turns out that the disc is made of some sort of RF absorbent
foam covered by a weather-proofing coating of some sort.

If one were to try to home-brew something like this, where
would a small piece of the RF absorbent material be obtained
without having to spend too much $$ for this experiment?

Thanks for any feedback on this!!

Mike Baker
WA4HFR


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