On Fri, 27 Aug 2010 11:56:06 -0400, n8de@thepoint.net wrote:
>I stick with Belden, Times, and other major manufacturers.
Last year, I helped N6RZ's widow clean out his shack and dismantle his
antennna farm. There was a lot of coax, almost of all of it good stuff
-- Belden, Times, and Amphenol, and a few pieces of off brand crap. I
can only guess about the vintage, but Times and Amphenol part numbers
don't Google. :) There was RG17, 214, 1/2-in and 3/4-in Andrews heliax,
etc.
I took some of it to an NCCC meeting the month before CQP to auction it
off. All the guys turned their noses up at it -- I couldn't give it
away. So I bought all of it -- paid a fair price for the hard line,
cheap for the coax they wouldn't take. Measured it with my HP generator
and spectrum analyzer. With the exception of the few pieces of off-brand
crap, all of it measured up to original specs. I used it to build a nice
set of stubs.
The stuff that had been on antennas had probably been there for 10-20
years at least. Dave had three go-rounds with cancer over a period of 30
years, and it was the fourth round that killed him. Once he had that
first bout, he didn't do much climbing. Some of the jackets looked awful
-- his QTH was at the top of a ridge, lots of sun exposure. All the
connections were very well taped and sealed. When I cut open jackets to
install new connectors or cut a stub to length there was visible
corrosion, but everything measured just fine at HF. The stubs are in use
in my HF station, which runs legal power, and working just fine. Loss in
a stub will show up as a reduction in the depth of a null. The old coax
measured just as well as new stuff.
Now, all of my work has been directed to HF, not VHF or UHF, and I might
be pickier if I were using this stuff at 144 or 432 MHz, or in a
repeater, where extremely good shield integrity is needed. Another very
important point -- at HF and low VHF, virtually ALL loss in coax is due
to IR loss in the center conductor and shield. Dielectric loss doesn't
become a factor in good coax until you hit at least 500 MHz. Yes,
moisture in the dielectric can lower that frequency. Yes, serious
corrosion can increase the resistance of the shield. But with the
exception of those few pieces of off-brand junk, I didn't observe any of
it in Dave's old stuff, nor in some old Belden of my own that I bought
at least 30 years ago.
73, Jim Brown K9YC
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