Bill and all,
This is probably no secret to most of you, but true 9913 and other
air-dielectric cable (Flexi-4XL, etc.) is fragile stuff. To get the benefit
of the lower loss you need to be sure you aren't creating impedance bumps by
melting the plastic spiral dielectric standoff when you solder on connectors
or destroying the coaxial spacing by installing too tight a radius or
otherwise crushing the cable. Even pulling the cable ties too tight when
you strap it to the tower can crush it. This is also true, to a somewhat
lesser extent, of foam dielectric cables. This stuff is a common topic of
discussion among the AMSAT crowd and most feel (and I agree) that to get any
real benefit out of this cable you need to install mil-spec N-connectors or
other similar professional product. Forget about PL-259 (UHF) connectors on
9913. If you are going to solder on connectors you might as well just use
good RG-213. It's much more rugged and if you are careful you won't destroy
the dielectric by soldering. There are crimp-on PL-259s that at least won't
melt the dielectric when you install them, but they aren't as water
resistant as good N-connectors and they aren't constant impedance
connectors, which matters in some cases. These air-dielectric cables make
great pipes to run water into the shack if you don't seal the outdoor ends.
You don't want water leaking into the cable from around the connector nor do
you want it coming through the connector (say from a cracked balun...
personal experience on that one). Mil spec and similar design N-connectors
are supposed to be nearly waterproof. If you add a good tape job over the
outside of the connector you won't have the unpleasant experience of finding
a big puddle of water on your desk during a rain storm. There are numerous
good ways to do that. I like using a combination of Scotch 23 rubber
splicing tape and either Scotch Super 33+ (7 mil) or Scotch Super 88 (8.5
mil) tapes. Some like electrical tape with Coax Seal (which I believe is
the same stuff as the gutter seal you can buy at hardware stores), some use
liquid products (Scotchkote, liquid electrical tape, etc.) in combination
with the electrical tape. Almost everyone uses electrical tape as part of
the combination. Please, get good electrical tape, not the discount
home-center brands. It's hard to beat the two Scotch products I listed
earlier. Steve, K7LXC, sells this stuff on his website (no financial
interest here) and I believe I have also purchased Scotch 23 there. He has
also published a good tutorial on how to use the stuff, as have many others.
In a recent post here on TT, WC1M, Dick, mentioned Kellems grips. If you
don't know what they are, check out K1TTTs Technical Reference at
http://www.k1ttt.net/technote/cable.html. Hubbell-Kellems actually does
have an online catalog now. It's here:
http://www.hubbellcatalog.com/wiring/catalogpages/section-t.pdf. The
section of interest to us starts on Page 28. These things (Kellems grips)
are an ideal solution to the problem of supporting a long vertical drop of
heavy cable without it being crushed due to its own weight. A look at the
TT archives shows that they have been mentioned here previously. Guess I
missed that while I was off the reflector for a few years. Anyway, hope
this will benefit some of the folks new to the reflector.
The opinions expressed above on the worth(lessness) of solder-on PL-259s are
those of the author. Others may love them. No flames, please.
73 - JC, k0hps@amsat.org
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Bill Aycock
Sent: Friday, July 01, 2005 3:01 PM
To: Craig Clark; towertalk@contesting.com
Subject: Re: [TowerTalk] replacing coax on a crank-up
Craig- This was a good contribution- But- I have a question or two about
the 9913. one- did you use common 9913 or one of the more weather-proof
varieties- two- if common 9913, how did you treat it to improve the
end-sealing?
Thanks- Bill-W4BSG
At 02:51 PM 7/1/2005 -0400, Craig Clark wrote:
> > 1. crank ups and coax (George M. Badger, III)
>
>Hello George et al,
>
>For most HF applications, a good RG213 is more than adequate for feeding
>antennas on a crank-up tower. That said, with my Tri-ex W67, I used Davis's
>Buryflex: since I sell it, why not use it.
>
>I cycled my tower ever year to lubricate the top bearing and eye-ball the
>connections to ensure that they were water tight. The Bury-flex was up for
>years and showed no signs of degradation from water or UV rays and was not
>damaged when the tower crashed, hi hi.
>
>Standard LMR400 is not the best choice as it has a solid center conductor.
>If you want to use LMR, use UF which has a stranded center conductor. The
>loss numbers on LMR400 and Buryflex are about the same. Bflex is a bit more
>expensive due to its burial grade outer layer of plastic.
>
>When you engineer the coax you have to take in to account the length from
>the shack to the base of the tower and then up the tower. I chose to secure
>the coax and rotor cable to the standoffs so you had to calculate the
>length of each loop. I found this to be better than letting the cable have
>free run.
>
>I ran a low loss coax, 9913, from the shack to the antenna switch at the
>base of the tower. I then ran Bflex to each of the antennas. I had on this
>tower:
>
>Cushcraft:
> X-7
> 5 element 6 meter
> 19 element 2 meter
> 146/440 dual band vertical
>
>I can't imagine using RG214 unless you already have it. Especially if it is
>silver plate. $$$$$
>
>Good luck.
>
>
>73, Craig Clark, K1QX
>
>RADIOWARE AND RADIO BOOKSTORE
>PO BOX 209
>RINDGE NH 03461
>603 899 6957
>WWW.RADIO-WARE.COM
Bill Aycock - W4BSG
Woodville, Alabama
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
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