If I went into most places selling cables I'd get laughed at if I took that
line, they'd say 'hie me to a research lab, if not an actual nunnery'. Not
that you're wrong, but if you want a single general purpose cable for HF and
VHF especially if stocking it for general sale, then there IS a 'best' cable,
defined simply by that which most likely serves the wide range of purposes at
a low price. Currently in the UK that cable seems to be RG6; few places like
to stock more than one type for RF if they think one will do. Perfectionism
is NOT the first base. It's reasonable to expect some standard without being
told to either become an expert or use a bell wire and stay in ignorance. RG6
works, but they sell it for VHF/UHF, not RF. I'm not so concerned with
moderate losses, but SNR maintained by good shielding matters to me.


You seem to miss the point that one shop's RG6 (or most other RG cables)
may well not be the same as another's. So there is no definitive answer
to you question.

It is also very unlikely that 'good shielding' will have any effect on
SNR in most applications, other than due to increased loss if the
braiding is very very poor, or you are running the cable very close to a
source of broadband interference.

Jeff

Fred wrote in
:


If I went into most places selling cables I'd get laughed at if I took
that line, they'd say 'hie me to a research lab, if not an actual
nunnery'. Not that you're wrong, but if you want a single general
purpose cable for HF and VHF especially if stocking it for general
sale, then there IS a 'best' cable, defined simply by that which most
likely serves the wide range of purposes at a low price. Currently in
the UK that cable seems to be RG6; few places like to stock more than
one type for RF if they think one will do. Perfectionism is NOT the
first base. It's reasonable to expect some standard without being told
to either become an expert or use a bell wire and stay in ignorance.
RG6 works, but they sell it for VHF/UHF, not RF. I'm not so concerned
with moderate losses, but SNR maintained by good shielding matters to
me.


You seem to miss the point that one shop's RG6 (or most other RG cables)
may well not be the same as another's. So there is no definitive answer
to you question.


No, haven't missed that at all. Most of my time is spent looking at all the
RG6's out there and examinng that. Besides, most advice out there implies I
have to buy it and try it to be sure, which is stupid because it's cheaper
and faster to get a better cable! RG6 is specified for UHF, I want HF.

It is also very unlikely that 'good shielding' will have any effect on
SNR in most applications, other than due to increased loss if the
braiding is very very poor, or you are running the cable very close to a
source of broadband interference.


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.

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'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.

Lostgallifreyan wrote:


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.

Are their any good references with test numbers on this? Been googling a
bit, haven't found anything definitive yet

- 73 de Mike N3LI -

On Wed, 03 Feb 2010 11:41:18 -0500, Michael Coslo
wrote:

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.

Are their any good references with test numbers on this? Been googling a
bit, haven't found anything definitive yet

Hi Mike,

With the CM performance being tied to foil application, such a
non-starter is bound to have only the whisp of academic research into
it if you expect to find test numbers. On the other hand, there's
sure to be a forest fire of testimonials.

To help in your search, try googling "cable transfer impedance." The
first page of responses should have a wealth of information.

73's
Richard Clark, KB7QHC

Michael Coslo wrote in
:

Lostgallifreyan wrote:


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.

Are their any good references with test numbers on this? Been googling a
bit, haven't found anything definitive yet

- 73 de Mike N3LI -


Not that I know of, I only saw this one:
http://www.bluejeanscable.com/articles/shielding.htm
It even describes cable transfer impedance so I guess it IS useful for other
than 'telling me what I want to hear'.

I just went for braided BT2002 because I know I can reuse it. I originally
found some in a telephone exchange skip, and had used it to extend UHF TV
antenna when I had a TV, many years ago, and later for a VHF dipole. I know
that a good braid covering is good for strong AF, so it seemes highly likely
that it will work on HF just as well if it's that good on frequencies on
either end of it.

On Sun, 31 Jan 2010 08:56:41 -0600, Lostgallifreyan
wrote:

Fred wrote in
:


If I went into most places selling cables I'd get laughed at if I took
that line, they'd say 'hie me to a research lab, if not an actual
nunnery'. Not that you're wrong, but if you want a single general
purpose cable for HF and VHF especially if stocking it for general
sale, then there IS a 'best' cable, defined simply by that which most
likely serves the wide range of purposes at a low price. Currently in
the UK that cable seems to be RG6; few places like to stock more than
one type for RF if they think one will do. Perfectionism is NOT the
first base. It's reasonable to expect some standard without being told
to either become an expert or use a bell wire and stay in ignorance.
RG6 works, but they sell it for VHF/UHF, not RF. I'm not so concerned
with moderate losses, but SNR maintained by good shielding matters to
me.


You seem to miss the point that one shop's RG6 (or most other RG cables)
may well not be the same as another's. So there is no definitive answer
to you question.


No, haven't missed that at all. Most of my time is spent looking at all the
RG6's out there and examinng that. Besides, most advice out there implies I
have to buy it and try it to be sure, which is stupid because it's cheaper
and faster to get a better cable! RG6 is specified for UHF, I want HF.

I have 5 runs of RG-6 (foil plus braid) running in a conduit with 2
LMR-600 cables carrying 1500 watts of RF at HF. I also have 3
CAT6 network cables in there. None of them hear the others.


It is also very unlikely that 'good shielding' will have any effect on
SNR in most applications, other than due to increased loss if the
braiding is very very poor, or you are running the cable very close to a
source of broadband interference.


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.

It's the shield, of which the braid is only part. Only if you are
running the RG-6 with other HF cables *might* you find a problem. As
I said above, I have 5 of them in the same conduit with cables
carrying 1500 watts of HF RF and there is no cross talk. That thin
foil is just fine at HF as well as UHF as long as it's not carrying
substantial power. Where you really need the extra shielding is at
very low frequency,or very high power. They do make quad shield RG-6
for receiving, but it's not a cable for high power transmitting. I'd
not put more than 100 watts into RG-6 of any configuration.

73 and good luck,

Roger (K8RI)



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.