On Mon, 21 Feb 2005 10:33:29 -0800, Roy Lewallen
wrote:
Is a material that is "high loss" at microwave frequencies always "high
loss" at HF? How "high" does the loss have to be in order to detract
from an HF antenna's performance when used as an end insulator? When you
put an object in the microwave oven for a minute with a glass of water
and the temperature rises 10 degrees C, how "high" is the loss? How
"high" is the loss at HF?

You're right, it doesn't even qualify as a SWAG! Hi!

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

It probably doesn't. I had just heard it was a way
to tell if the PVC had some kind of metal particals,
or whatever. I'm not that much up on PVC, but the rumor
I had heard was the "grey" PVC was better for HF rf use
compared to the white stuff. But I don't really know.
I've tried both, and never had any problems. The loading
coil on my shorter mobile antenna is wound on grey PVC,
and so far, I've never noticed any adverse effects.
My 2nd antenna uses a thin plastic tube, about like what
you would see on a sidewalk blower, or whatever...
Never noticed any problems with it either. I seem to have
about the same performance as an open frame coil, as far
as I can tell, and I've never noticed any heating, or
melting, etc..
My comment was more to protect the microwave, rather
than endorse the value of PVC nuking...:/ I have
tried it though...The grey stuff does stay cold when
nuked...Whatever thats worth..I didn't try the white
though...I've never had trouble with any material as far
as end insulators...I've run legal limit through plastic
coathangar insulators 3 inches long, and didn't arc...
That I could tell anyway...Same for PVC or wood...
The only time I've ever arced, was when the bare wire was
actually rubbing a tree branch...I started to burn it
up...Probably had been that way 2 weeks before I noticed
it..
MK

Roy Lewallen wrote:
Is a material that is "high loss" at microwave frequencies
always "high loss" at HF?

Roy, we know you are into quantitative stuff but some
of us are into qualitative stuff. We know not to put
our hands into a flame even though we have no idea what
is the temperature of the flame or what temperature our
hands reach when put into a flame. If the exact temperature
of a flame Vs a blister on your skin is important to you,
why not experiment and report? :-)
--
73, Cecil http://www.qsl.net/w5dxp

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On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:

It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.

Roy Lewallen, W7EL

The microwave test was written up in Hints & Kinks, 13th edition, page
6-6, although no scientific explanation was given as to why warmed
plastic would be worse than cool, after 2-3 minutes nuking on "high"
with a cup of water also present. (Author was E.R. Berg, KZ9Y.)

bob
k5qwg



wrote:
I'd also add a glass of water in the microwave when you do
that...I'm not sure if they are still that way, but it used
to be bad for them to run with no load...IE: food...MK