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[Towertalk] cable TV hardline

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Subject: [Towertalk] cable TV hardline
From: (Steve Katz)
Date: Fri, 9 Aug 2002 13:44:30 -0700
> Hi,
>       I have a question regarding your mention of not doing this sort
>       of thing on vhf/uhf.
>       I am preparing to let some friends temporarily place some vhf/uhf
>       antennas on my tower in order to operate a contest.  For 6 and 2
>       meters, I was going to feed the antennas with BuryFlex coax, but
>       for 432 I was going to do something with CATV hardline.  (The feed
>       line length will be about 110 feet.)
        [Steve Katz]  9913 and variants of it only have about 2.7 dB/100'
loss on 432 MHz.  CATV hardline probably cuts that to about 2.0 dB, not a
huge advantage.  I probably wouldn't bother with the hardline unless I was
out of regular 50 Ohm low-loss cable...

>       Was your remark meant to indicate that proper 50-to-75 ohm baluns
>       should be used instead of no baluns, or that 75 ohm hardline should
>       not be used? 
        [Steve Katz]  Neither.  I was remarking about making lousy splices
in coaxial cable, like just soldering center conductors together, using a
screw to attach the outer conductors, and sticking it in a bottle or
something, like one post discussed.  Those kind of splices work fine on 160
meters, and not very well on 70 cm!  I used 75 Ohm CATV hardline for many
years on 50-144-220-432-903-1296 MHz and had very good luck with it, without
using any 50:75 Ohm Ununs.  There's no reason I can think of to use matching
transformers, even if they were completely lossless, since I could always
adjust any antenna I had, including Yagis, Quagis, Loop Yagis, corner
reflectors, dishes -- anything -- to be 75 Ohms, and then there's no
mismatch, and no added mismatch loss in the coax.  The only tricky thing is
how to measure the results, since nearly all test and measurement
instrumentation for RF, and virtually anything hams have, is all normalized
50 Ohm equipment.  So, while a wattmeter (or whatever) indicates power in a
75 Ohm line, it doesn't indicate the correct amount of power.  For me,
that's kind of a "so what?" but it might bother some people...


>  I don't want to do the wrong thing here, especially
>       if it will damage their radios.  (I do not have vhf radios, except
>       an old dedicated packet rig.)
>       Many thanks.
> 73, Dave Clemons K1VUT
> Dave Clemons
> Evans Griffiths & Hart, Inc.
> 55 Waltham Street, Lexington, MA 02421
> (781)861-0670, (781)860-9321 (Fax)

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