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October 9th 03, 06:34 AM

Tom Bruhns

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(Tom Bruhns) wrote in message om...
....
(Example: RG174 at f=30MHz will have a bit more than 3.4dB/100 feet
loss because of R, and probably well under .025dB/100 feet loss
because of G. See Roy's suggested reading for the source of those
numbers.)

It's also worth pointing out that if you use the same dielectric
material in a line with larger diameter, the R loss -- the loss in the
resistance of the wire -- drops, but the G loss stays the same. So
for a 1" diameter solid polyethylene dielectric 50 ohm line with
smooth copper conductors, at 30MHz the attenuation is about
0.214dB/100ft, and the attenuation due to G is perhaps 1/10th that
much. At 3000MHz, the coax probably still propagates pretty well in
TEM mode, and the R and G losses will be nearly the same and each
about 2dB/100ft.

Because of the higher losses in fiberglass-epoxy PC board material,
you can fairly easily end up with stripline which has higher G loss
than R loss, when using that board material in the GHz range. (Howard
Johnson recently had an article about this topic in, um, EDN or
Electronic Design, I can never remember which his column appears in.)

Cheers,
Tom

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