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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