On Mon, 7 May 2012 19:17:58 -0500
Mike Waters <mikewate@gmail.com> wrote:
>it would be interesting to
>experiment with some
> CAT5/6 sometime, just for the fun of it. :-)
>
I did that. I was testing a small dual-feed DHDL loop (-50
dBi gain) using twisted pairs removed from a CAT 5 cable.
On the bench the twisted pair showed 100 ohm of impedance
and a loss of about 2.8 dB at 1.8 MHz on a 100' run. (I
also tried CAT 6. The results were the same. The
difference between CAT 5 and CAT 6 is that the CAT 6
pairs' twists are more precisely controlled, which results
in a more uniform impedance and lower losses at the upper
end of the spectrum.)
I was running two 16 foot lenghts of twisted pairs, one
from each element, into a phasing/combiner box, which had
carefully designed balanced-transformer inputs. The
twisted pairs had #31 common mode chockes every 4 foot.
While the twisted pairs worked, despite the balanced
arrangement, there was more common mode (BC and noise)
pick-up than the same runs using (non-balanced, but
grounded) RG-179 cables. The RG-179 cables had the same
#31 chokes as the twisted pairs. I attribute the
performance difference to the fact that the shields of the
coax cable were grounded, while the twisted pairs were
"floating".
I believe that if one wants to use a balanced arrangement,
twinax may be the ultimate solution. Otherwise, just stick
with good quality RG-6.
73,
George
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