Sorry, I strongly suspect this is a very old can of worms I'm exhuming, but
here goes...

The web is full of advice (and noise) about RG6 being better than RG59, but a
small proportion of experience-based postings suggests that RG59 is often
adequate even where UHF signals are used, especially if it includes a foil
shield under a braid shield, and it has a foam dielectric. Less common is a
point suggesting that for HF (and perhaps CCTV and other video, as well as
S/PDIF digital audio) it might be better to use RG59 because its braid is
better at screening for these lower frequencies to get better SNR. This seems
to make sense, but it is it so? It appears to me that for domestic scales an
RG59 with the added foil shield and a foam dielectric might be the best coax
to use for low power signals, until some weakness dictates a specific
requirement for improvement.

Lostgallifreyan wrote:
Sorry, I strongly suspect this is a very old can of worms I'm exhuming, but
here goes...

The web is full of advice (and noise) about RG6 being better than RG59, but a
small proportion of experience-based postings suggests that RG59 is often
adequate even where UHF signals are used, especially if it includes a foil
shield under a braid shield, and it has a foam dielectric. Less common is a
point suggesting that for HF (and perhaps CCTV and other video, as well as
S/PDIF digital audio) it might be better to use RG59 because its braid is
better at screening for these lower frequencies to get better SNR. This seems
to make sense, but it is it so? It appears to me that for domestic scales an
RG59 with the added foil shield and a foam dielectric might be the best coax
to use for low power signals, until some weakness dictates a specific
requirement for improvement.

If there was a "best" cable, there would be only one type. Some have
lower loss, some are more flexible, some have better weather resistance,
some have better shielding, some have a longer lifetime, some tolerate
temperature extremes better, some are more uniform, some are less
expensive, and so forth.

So deciding which cable is "better" requires a lot more information
about what your requirements are.

RG/U specs have long been abandoned by the military, so any manufacturer
can -- and do -- use these designations pretty much as they please. One
manufacturer's "RG-59/U" or "RG-59/U type" cable can be very different
from another's, in many important ways. So you have to look at the
specifications of the actual cables you're comparing.

That said, RG-6 is nominally larger in diameter than RG-59, so if
everything else is the same, it will have lower loss, be heavier, more
expensive, and less flexible.

Multiple shields are seldom important in amateur applications unless you
have some seriously strong local signal you need to keep out, or you
need to bundle several cables tightly together for a long run. Even
then, most amateurs will end up with a lot more signal leakage at other
points in the system than they'll get through a good quality single shield.

Speaking of shields, some cheaper cables have relatively poor coverage,
so a decent quality shield is sometimes a good investment. Adding foil
might make a poor shield better. But I have some popular foil-shielded
cable that has bizarre loss characteristics at around 400 MHz which vary
all over the map as the cable is flexed. So a poorly designed foil
shield can be worse than a decent braided one.

Foamed dielectric results in slightly lower loss. At UHF and below, this
is almost entirely due to the fact that it causes the center conductor
to be larger, reducing conductor loss. On the other hand, the velocity
factor and impedance vary a lot more from lot to lot than solid
dielectric cable, so in length-critical applications you'll need to be
able to measure the electrical length of each piece.

That's the five minute coax cable primer. If you dig a bit you'll find
out there's a lot more to it than this.

Roy Lewallen, W7EL

Lostgallifreyan wrote in
:

....
sense, but it is it so?

I wrote some notes that you may find interesting at
http://www.vk1od.net/transmissionline/RG6/index.htm .

Owen

Owen Duffy wrote in
:

Lostgallifreyan wrote in
:

...
sense, but it is it so?

I wrote some notes that you may find interesting at
http://www.vk1od.net/transmissionline/RG6/index.htm .

Owen


Very useful, though I'm still not clear about using it for HF. I found eBay
listing 270364333691 (worth seeing, low cost, good pictures and description),
but that shows a thin braid and film that I read might not be adequate for
shielding at HF. Low cost is great but I wonder if trying to get good
connections to aluminium braid will be more trouble than it's worth, if the
worth of a cable with a copper braid isn't that much higher. (Still looking
for one). The cable that seems most likely to work based on all I read is a
BT2002 cable with a double copper braid over a foam dielectric and stranded
core, but the cost is three times higher.

Roy Lewallen wrote in
:

If there was a "best" cable, there would be only one type. Some have
lower loss, some are more flexible, some have better weather resistance,
some have better shielding, some have a longer lifetime, some tolerate
temperature extremes better, some are more uniform, some are less
expensive, and so forth.

So deciding which cable is "better" requires a lot more information
about what your requirements are.


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.

I take your point about poor foil/braid shields being worse than good braids.
That's partly what drove my question. It seems to me that RG6 in all forms I
have found is optimised for VHF and higher. Nothing I've seen either before
or after that question has yet convinced me that RG6 is the better choice for
HF. I've seen plenty of posts saying it will work, but just as many saying
they've seen old RG59 cables doing fine at UHF too.

So far I think I'm likely to go with the more costly double braided BT2002.
Most posts I read stated that poor performance was usually due to
difficulties connecting firmly to the soft aluminium shield than to the
cable's own qualities. I suspect the extra cost for double copper braid will
be repaid in easier (soldered) connections and other savings elsewhere, plus
a certainty that it is effective at HF. I'm not going to be using it for UHF
(although I have done once, it worked ok for a long TV aerial extension), and
I've already used it for VHF with good results. Main thing with the BT2002 is
that it's old, there might be something directly equivalent made for British
Telecom data links now, perhaps thinner, or cheaper, or more flexible, but I
don't know how to check for that. I've seen a list of BT type cables but I
think it was as old as that cable is.

Last time I got the BT2002 I found it, didn't have to pay for it. The only
thing making me wary of it now is that it won't be free this time.

Lostgallifreyan wrote:
Roy Lewallen wrote in
:

If there was a "best" cable, there would be only one type. Some have
lower loss, some are more flexible, some have better weather resistance,
some have better shielding, some have a longer lifetime, some tolerate
temperature extremes better, some are more uniform, some are less
expensive, and so forth.

So deciding which cable is "better" requires a lot more information
about what your requirements are.


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. . .

Sounds like you have your answer, then.

Roy Lewallen, W7EL

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

Roy Lewallen wrote in
:

Lostgallifreyan wrote:
Roy Lewallen wrote in
:

If there was a "best" cable, there would be only one type. Some have
lower loss, some are more flexible, some have better weather
resistance, some have better shielding, some have a longer lifetime,
some tolerate temperature extremes better, some are more uniform, some
are less expensive, and so forth.

So deciding which cable is "better" requires a lot more information
about what your requirements are.


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. . .

Sounds like you have your answer, then.

Roy Lewallen, W7EL


Yes, if I was using for UHF and perhaps VHF as they sell it for. But as far
as I know the older UG59 used a braid with better physical coverage and was
specified for HF as well. I'd rather get something this time that has good HF
shielding as priority, so I'm not convinced that RG6 is the right choice. A
bit of extra loss isn't as bad as poor shielding.

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.

Lostgallifreyan wrote:

Yes, if I was using for UHF and perhaps VHF as they sell it for. But as far
as I know the older UG59 used a braid with better physical coverage and was
specified for HF as well. I'd rather get something this time that has good HF
shielding as priority, so I'm not convinced that RG6 is the right choice. A
bit of extra loss isn't as bad as poor shielding.

The standard for cable tv and satellite instalations is RG6 "quad shield",
which has a less dense braid, but a (almost) 100% aluminum foil shield.

The question is how do you connect to it? Commerical applications use special
crimp on connectors, you can solder it with the proper flux.

A friend brought some Radio Shack screw on PL-259 connectors that work fine
with it, but they are $6 each in the US, and unavailable here.

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.