[Amps] Lossy rod stock for coils

["John T. M. Lyles" <jtml@lanl.gov>]

Neil, G0JHC, asked:
> Although I see a number of articles (here in Europe) suggesting PTFE or
> Tufnol maybe used in the applications mentioned, I rarely see anyone using
> Tufnol.
>
> In order to "get wise" on the pros & cons of both materials I did a web
> search and found VERY little information on Tufnol rod in general. I asked a
> friend in the USA who builds amps and he said he had never heard of the
> stuff.
> My question is:
> (1)     Is Tufnol a European "thing"?
> (2)     Is one "better" than the other?

I did a search on the web and found that Tufnol is a big distributor 
of plastic materials in Europe. It is not a particular material 
formulation. They could supply rod stock in many different materials 
and some are not suitable for use in RF fields.
http://www.tufnol.com/machine.htm

Saying you have Tufnol rod is similar to me saying I have some Dupont 
plastic rod to try. You might need to describe the particular rod you 
hav by texture, feel, color. As you know PTFE (Teflon PFE And PTFE) 
will have a slippery white surface most times.

Your microwave oven test suggests it should not be used in high RF 
fields, if it got so hot in only 2 minutes in the oven with water 
load "in parallel":

Putting a cup of water in the oven does reduce the field available to 
heat the plastic under test.
While it loads the maggie (magnetron), if the plastic has any loss at 
all, it will also provide load. I assume then that the water is 
needed in case you have a nice piece of PTFE in there, which is 
hardly any load at all - to prevent arcing/cracking your magnetron 
from the reflected power. I have found that Amana microwave ovens are 
great for testing as they don't need any water load - they have a 
slightly lossy glass shelf in the bottom. Their "ballast" .

I use a WT LaRose 90 MHz 1 KW RF dielectric preheater, which I found 
at a local surplus equpment place. With paralllel plates for the 
'applicator' end, it will take most plastics into meltdown in a few 
minutes if there is any loss at all or any moisture in it. I use it 
to qualify hose material, insulator material, supporting pieces, for 
use in high power amplifiers at work. Teflon blocks will barely warm 
in the preheater.

73
John
K5PRO

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