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.


Dear Roy,
Perhaps that is not the objective, Roy - maybe the rationale' is
simply to decide whether or not a particular sample of material is a
"high loss" dielectric or not.

Regards,

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

Bob, W9DMK wrote:
"-maybe the rationale is simply to decide whether or not a particular
sample of material is a "high loss" or not."

I think that`s it. The properties of dielectrics are functions of
temperature and frequency. My CRC Handbook of Chemistry and Physics
shows PVC`s dielectric constant is definitely a function of frequency,
unlike polystyrene and some other pastics.

I`ve seen PVC used as a base insulator for vertical elements of a HF
antenna array, and it worked OK.

I think low power factor and dissipation=A0are desirable for an
insulator. My 1987 edition of the ARRL Handbook has a table 47 on pages
35-36 and 35-37 titled "Properties of Common Thermoplastics. Maybe later
editions have expanded tables.

Best regards, Richard Harrison, KB5WZI

W9DMK (Robert Lay) wrote:
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.



Dear Roy,
Perhaps that is not the objective, Roy - maybe the rationale' is
simply to decide whether or not a particular sample of material is a
"high loss" dielectric or not.

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?

Roy Lewallen, W7EL

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

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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