Robert Atkinson wrote:
You beat me to it Bruce!
They call it a Stealth(tm) Ground Plane. It's used in the Zephyr Geodetic 2
antenna.
See
http://www.trimble.com/infrastructure/pdf/gnss-choke-ring-antenna_brochure.pdf
"proper" attenator materials (Eccosorb by Emerson & Cuming and I think Grace make some) are expensive, but I've had some luck with carbon loaded anti-static foam in the past. I've used it to kill enclosure resonaces for EMC and at around 4GHz to reduce skin leakage and ground reflections when testing aircraft radio altimeters on the ground.
Robert G8RPI
I have used Carbon fiber fabric from the hobby shop and I have used
rubber from tires found along the road.
This is at 10 GHz so I don't know how it would work at 1.5 GHz
Bill K7NOM
--- On Thu, 25/3/10, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote:
From: Bruce Griffiths <bruce.griffi...@xtra.co.nz>
Subject: Re: [time-nuts] Poor man's choke ring
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Date: Thursday, 25 March, 2010, 1:18
Neville Michie wrote:
If I understand the choke ring antenna it is to remove signals propagating
across the ground plane.
Now if there was a very lossy layer on the ground plane any signals propagating
across it would be attenuated.
For instance, if you find a plastic that melts in your microwave, a sheet of
that plastic over your ground plane should work.
Or do plastics that attenuate enough not exist?
cheers, Neville Michie
Trimble produce an antenna with a dissipative ground plane.
Bruce
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