"Geoffrey S. Mendelson" wrote in
:

I can only guess you situation, but if you can do it, I would just go
to a supplier you trust and buy RG6 and see if it works. While I'm sure if
you had the right equipment you could find differences in the noise that
comes through various RG6 versions, it may not be enough to matter.


Well, that's maybe first choice. Just haven't decided if I'll stump up the
£18 or wait and search a bit longer for more info.

My situation is an HF antenna that will bring a signal from several tens of
metres away, into a building with stuff likely to put RF at several
frequencies onto the line. I'll filter out what I don't want with a selective
'tuner' eventually, but whether I do that or not I still have to reduce
common mode noise that is in same band as signals I want. I'll be using
ferrite slugs to reduce this, but I learned that this works by blocking skin-
effect carriage of RF signals on the outside of the coax shield, reducing
common mode noise by making current in the shield balance that in the core.
This implies that when a skin effect carries current down the outside of the
shield, but is not equal (and inverse) to current in the core, it must be
balanced by current on the inside of the shield instead. In transmissions,
I'm told this can turn a shield into an emitter, and though I'm receiving the
inverse is true, so I don't want the shield to pick up local noise and feed
it to the input via imbalances between shield and core. So if this use of
ferrites relies on suppressing signals in skin effect current flow, and HF
skin effect thickness are thicker than those for UHF, it seems to follow that
a metallised plastic film is too thin. It appears that a shield for HF must
be at least twice as thick as the skin effect depth for HF. RG6's foil or
metallised plastic seems too thin, and while the braid is thick enough, its
physical coverage is poor. I think it's mostly there to ensure continuity of
foil as a guard against UHF noise when foil cracks on bending, and as a means
to anchor a connection.