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