I've been told that braid makes a great deal of difference to common mode
noise pickup, and that while a thin foil and loose braid is fine at UHF it's
not to be expected to do the same for HF.

Even if you accept the principle that foil is worse than braid for
common mode signals, where do you think these signals are coming from?
Unless the cables route close to the source of the interference then
your antenna is going to pick it up much more than any difference in
shielding.


http://www.abccables.com/info-rg59-vs-rg6.html is one of the more descriptive
texts I read. No RG6 that I have found fits the description given there for
HF. RG59 does though, as does BT2002. I think I'll be going with that BT2002
anyway, never mind the expense. The waste of time trying to avoid it is alone
beginning to look more expensive than the price difference.

I must admit I do not understand the theory that foil is worse than
braid at lower frequencies, foil gives 100% coverage and is usually in
addition to braid. Even if it the thickness of the foil that is in
question, I don't see how, according to the article that you linked to,
it " don't(sic) have the proper type of shielding ".

There may be an issue with terminating foil shields well but that is a
different matter.

Jeff wrote in
:



I've been told that braid makes a great deal of difference to common
mode noise pickup, and that while a thin foil and loose braid is fine
at UHF it's not to be expected to do the same for HF.

Even if you accept the principle that foil is worse than braid for
common mode signals, where do you think these signals are coming from?
Unless the cables route close to the source of the interference then
your antenna is going to pick it up much more than any difference in
shielding.


True, but that's why I want it. It's to exclude HF noise made by anything in
the building. The antenna will be several tens of metres away. As the signals
I want are HF and perhaps high MF from that antenna, it seems unlikely that I
should go with a cable whose specs are too loosely defined, and all
interpretations of 'RG6' are now attempts to reduce cost while getting
acceptable performance at UHF.


http://www.abccables.com/info-rg59-vs-rg6.html is one of the more
descriptive texts I read. No RG6 that I have found fits the description
given there for HF. RG59 does though, as does BT2002. I think I'll be
going with that BT2002 anyway, never mind the expense. The waste of
time trying to avoid it is alone beginning to look more expensive than
the price difference.

I must admit I do not understand the theory that foil is worse than
braid at lower frequencies, foil gives 100% coverage and is usually in
addition to braid. Even if it the thickness of the foil that is in
question, I don't see how, according to the article that you linked to,
it " don't(sic) have the proper type of shielding ".


Well, that's why I'm questioning it here. Like Geoffrey Mendelson said in his
reply in the later thread on RG6 in this group, a lot of the posts I've seen
on the web say more about the posters making them. I think I'll get a better
signal here than on the web at large. No irritating forum signups before
posting, either.. That article does seem to have a few vague contradictions,
but I think the point about a thin foil that is adequate for UHF screening
being inadequate for HF is interesting, and I've seen that point claimed
before. I'm pretty sure I'm not going to get an answer for that from people
who are dealing with UHF or fast digital signals, and mainly from an
installer's point of view, if the equipment they're using will filter out HF
anyway. Their purpose is not the same as mine.

There may be an issue with terminating foil shields well but that is a
different matter.


I found an RG6 with copper braid, to take care of that. Cheap too, but only
if it works. If it doesn't it will be cheaper to go for better cable to start
with. I like that BT2002 with the double copper braid, but I'm not yet sure
if the difference justifies the cost, though judging by what some places
charge for RG6 it probably does..

Lostgallifreyan wrote:
I found an RG6 with copper braid, to take care of that. Cheap too, but only
if it works. If it doesn't it will be cheaper to go for better cable to start
with. I like that BT2002 with the double copper braid, but I'm not yet sure
if the difference justifies the cost, though judging by what some places
charge for RG6 it probably does..

There also is the question of cost and availablity. I can go to Home Center
and buy for about $.50 a meter a decent quality RG6 quad shield. In other
places, you should be able to localy source it for less.

Radio type coax requires me to special order it at the local electronics
store, and it will be a lot more expensive and less likely to be what
I wanted.

I really do miss being in the US able to go into any one of 6 Radio
Shack stores near my home and buy RG8x (really just improved RG-58) or
RG-8 coax by the foot. It wasn't the best one could buy, it it was "good
enough".

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.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.

"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.