On Thu, Jun 21, 2012 at 10:40 AM, Jim Brown <jim@audiosystemsgroup.com>wrote:
> The other element of transfer impedance is the uniformity and
> density of the shield, often described as shielding effectiveness.
> Foil/drain shields designed for use at VHF/UHF (i.e., CATV coax) have
> fairly high resistance at 2 MHz as compared to something with a decent
> copper braid, so they're not great shields at MF and low HF.
>
I have recently replaced some "RG-6" in use for maybe seven or eight years.
I opened it up to see what was happening. The degree of oxidation on the
inside and outside of the foil was perplexing. One could easily draw a
thumbnail along either side and build up a little pile of oxide. The foil
itself had become very brittle. It had been "sealed" and treated outside.
If Jim says the shielding needs help when it's new, there's not much hope
for some varieties when it gets old. Another reason not to use anything
other than the flooded variety. Particularly so for someone who can look
at the ocean. I'm hundreds of miles from salt air. Would need to go with
flooded for sure close to the ocean.
The deterioration would be sneaky slow, and unless one had worked out some
kind of benchmarking for it, one would never know.
I've got flooded "RG6" to my phased loops-on-ground, and the over-the-air
outdoor TV antenna, and they're hanging in there so far.
73, Guy.
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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