At 10/15/2004 09:19 AM, you wrote:
>Duplexer companies that use RG8, 58, 213, or any of that noisy crap should
>be "burned at the stake" :)
...including Phelps-Dodge? I don't think so.
The only problem with the coaxes you mention is that the braid is not solid
or silver-plated. If any water gets inside the coax in any way, the copper
braid eventually oxidizes & generates IMD. The noise you get is probably
mixing between the TX carrier & its sidebands, which you induce when you
move the coax with it's millions of point-contact diodes. If the duplexer
is kept in a controlled environment (not outside), the cables shoudn't degrade.
I had a piece of RG-8/X used as a pigtail to a portable repeater antenna
that looked perfectly good on the outside, but generated noise such as you
describe. Cutting it open revealed the water infiltration. In fact, it
only generated noise when flexed in the area where water got in. Further
down the coax where the braid still appeared shiny there was no noise when
flexed. I replaced the pigtail with RG-142 & that solved the problem. The
fact that RG-142 is double-shielded is incidental; it's the silver plated
shield that prevents IMD generation.
Bob NO6B
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