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Re: PVC w/ H2O

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 09:56 PM 1/14/2007, Tesla list wrote:
Original poster: Gomez Addams <gomezaddams@xxxxxxxxx>

On Jan 13, 2007, at 7:44 PM, Tesla list wrote:

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>


Somewhere in the archives is a loss table for different types of
coil forms.
I think maybe Richard Quick compiled them. I any case, PVC does become
pretty lossey in the high freq spectrum.

Oh, absolutely!  I recently had to come up with a VERY low loss
radome for 5.3 GHz.  The only thing that was acceptable was thin
polyethylene.  Teflon would have been fine, but it's a bear to form,
and I had to have a closed-end cylinder.  I wound up using the bottom
of a 1 gallon vinegar jug!  Its presence was almost undetectable on
the network analyzer.

At work, we use Rohacell foam for this kind of thing. I also had a radome manufactured for a precision receiver (so we needed very low and consistent loss) that was kevlar composite over a kevlar honeycomb (I think).. the key was that the thickness of the sandwich was designed to have low loss at our angle of incidence (sort of like AR coatings on optical components).

My coil forms are coated 1/8" PVC.