Re: PVC w/ H2O

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Gomez Addams <gomezaddams@xxxxxxxxx>


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

> Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>
> Hello,
>
> 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.

> My coil forms are coated 1/8" PVC.

I have used the super thin-wall stuff (thinner than 1/8" even at 6"
diameter) and "foam-core" (sort of, not really, but a lot of people
call it that) DWV 1/8" or so for really large forms (12" diameter or
so).  Some day, I want to do a materials comparison of my own... some
day...

> I think the process of coating with polyurethane helps lesson the
> amount of
> loss as well.

It's possible.  I haven't thought about it much.  PVC being utterly
nonexistent to magnetic fields, the loss has to be due to the
electric field component.  Perhaps super-insulation helps that.

> Polystyrene is very cheap for smallish coils and is very low loss
> if you are
> in the high frequencies. I have a 4" form of this type for my
> future VTTC.

I have never seen styrene tubing.  Will have to think about that next
time!

 - B(G)L

...........................................
Al Queda doesn't have to conquer us, we'll
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