In message , Jerry Stuckle
writes
On 3/15/2014 9:18 AM, Ian Jackson wrote:
In message ,
Bob E. writes
75-ohm RG-6 coax: quad shield differs from "standard" RG-6 in that the
dielectric is reduced in diameter to accomodate the extra shielding.

How does this affect the performance? I'm looking at 1 GHz (HDTV use).

Thanks.

I note that there have been a some replies, but none seem to make much
attempt at answering your question.

RG6Q is used extensively in the UK cable TV industry as 'drop' cable -
ie from the taps in the street cabinet to the home. It is used to
provide a high degree of immunity from ingress of interfering signals -
especially those at the lower frequencies (in the reverse path part of
the spectrum - typically between 5 and 65MHz). RG6 is not a particularly
low-loss cable, and for long drop runs, RG11 is sometimes used.

As for the attenuation differences between RG6 and RG6Q, I've done a bit
of Googling, and I can't see anything which is immediately pointed out.
Even on this site
http://www.ehow.com/list_7605813_difference-between-rg6-rg6q.html
all it says is that "RG-6 and RG-6Q share nearly the exact same outer
dimensions and have similar flexibility. RG-6Q is slightly stiffer due
to the increased amount of inner shielding".

I suspect that even if the diameter of the RG6Q dielectric is slightly
less (something which I've never really noticed) - requiring a slightly
thinner inner conductor in order to preserve the Zo - the increase of
attenuation won't be very much. However, I'm sure that a bit more
intensive Googling on RG6 physical and electrical specs will reveal the
true answer!

No one has answered his question because the information is insufficient.

FYI - my company (a home automation company) installs thousands of feet
of coax every year (even more twisted pair). But we never specify what
to use until we know how it is being used.

Additionally, it depends if he needs to send send power over the coax
also, and if so, how much.

For instance, the new specs for HDTV (Ultra-hi-def, 3D at 240
frames/sec) require bandwidths of up to 18Ghz. It's something we have
to take into consideration on ANY installation.

Just saying it's going to be used for HDTV is not sufficient.

My immediate lateral-thinking guess is that the OP has acquired some
RG6Q, and is wondering whether he can use it as antenna drop cable for
UHF TV (which, in the UK, includes HD). He has specifically said that
it's for use at less than 1GHz. His main concern is probably that
quad-shield might be a more lossy than RG6 (which indeed it could be as
a smaller diameter dielectric would require a smaller diameter inner in
order to maintain a Zo of 75 ohms, and this would increase the
attenuation). Of course, he could also be concerned about some of the
many other parameters - but I suspect not. If it's not attenuation
that's concerning him, I'm sure he will tell us.
--
Ian

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