Hi Steve,
Thanks for the clarification! In the installations I referred to, the
RG-17 was
strapped to a 120 foot wooden pole with cable straps, so the gravity
explanation
seems right on. This was a professional (well, sort of, it was a
government cable
crew) installation. As the problem seemed to be common all over the
base, the decision
was made to replace all RG-17 with Andrews Heliax and the problem went
away! Again, all
the installations were vertical where the problem appeared.
Thinking back on it, the horizontal runs (underground in conduit) to the
HF Conical
monopole antennas never had the problem. They still use -17, but are
scheduled for
replacement in the Spring, due to the relocation of the HF transmitter
house.
Tnx 73 de Tom/W4OKW
Steve Katz wrote:
>
> Re: RG17...
>
> The center conductor doesn't shrink and withdraw the center pin. It, along
> with the dielectric, can literally slide inside the braided outer conductor
> and create the effect that you see, due to gravity and the incredible weight
> of this cable.
>
> I've used it for 35 years and have never had this occur, even once,
> following the prescribed instructions for use, which always include making a
> drip loop at the antenna feedpoint and binding that loop tightly to the
> tower leg or whatever's supporting the antenna. With a 360 degree loop in
> place, the slippage cannot occur. This cable cannot self-support vertically
> for any distance. If you use the same cable laying on the ground, you won't
> see the "slippage" or "shrinkage."
>
> -WB2WIK/6
>
> "If everything seems under control, you're just not going fast enough." -
> Mario Andretti
>
> > -----Original Message-----
> > From: fclarke [SMTP:fclarke@erols.com]
> > Sent: Tuesday, December 17, 2002 7:36 PM
> > To: Steve Katz
> > Cc: 'k3bz@arrl.net'; 'Tom'; towertalk@contesting.com
> > Subject: Re: [Towertalk] Coax
> >
> > RG-17 has a nasty habit of the center conductor shrinking and
> > withdrawing the center pin
> > from the connector. Drove us nuts trying to troubleshoot a repeater
> > problem a few years
> > ago.
> >
> > Our base electronics shop canned all the RG-17 and replaced it with
> > Andrews Heliax and
> > solved many problems. Of course it is easy when Uncle Sam is paying for
> > those $$$$$
> > connectors!
> >
> > Hardline seems to be showing up at hamfests and then there is always the
> > old standby -
> > ex CATV hardline. 75 ohm, but there are ways around that.
> >
> > 73 de Tom/W4OKW
> >
> >
> > Steve Katz wrote:
> > >
> > > Hi Jerry,
> > >
> > > I don't know anyplace in eastern PA, but if I lived there, I'll bet I'd
> > find
> > > one!
> > >
> > > Here in southern California, my usual source is Apex Electronics, 8909
> > San
> > > Fernando Road, Sun Valley, CA (818) 767-7202. They usually have miles
> > of
> > > it, still spooled, often with government contract tags still attached.
> > >
> > > Since 1000' of RG17A/U weighs about half a ton, it is expensive to ship.
> > > When I lived back east, I always had a more "local" source of such
> > items,
> > > but that was a very long time ago. I'd probably do a search (Yellow
> > Pages,
> > > etc) on "military surplus" and "military surplus electronics," "military
> > > surplus wire and cable," etc. to determine who the local sources are.
> > >
> > > Also, if you live near any military depots, they usually have auctions
> > > annually or so to dispose of stuff they don't need. I've attended such
> > > auctions at Picatinny Arsenal in NJ and NWCC in Mechanicsburg, PA years
> > ago
> > > and the deals are absolutely amazing. One I remember is picking up a
> > > 0-15Vdc, 0-100A regulated power supply (linear, and weighed about 200
> > lbs)
> > > for $50 in brand new condx. I couldn't lift it, so they helped me with
> > a
> > > pallet jack to get it into my station wagon...
> > >
> > > WB2WIK/6
> > >
> > > "If everything seems under control, you're just not going fast enough."
> > -
> > > Mario Andretti
> > >
> > > > -----Original Message-----
> > > > From: Jerry Keller [SMTP:k3bz@arrl.net]
> > > > Sent: Tuesday, December 17, 2002 9:10 AM
> > > > To: Steve Katz; 'Tom'; towertalk@contesting.com
> > > > Subject: RE: [Towertalk] Coax
> > > >
> > > > Steve... could you refer me to a source for that military RG-17A/U?
> > I'm in
> > > > eastern PA. Jerry K3BZ
> > > >
> > > > -----Original Message-----
> > > > From: towertalk-admin@contesting.com
> > > > [mailto:towertalk-admin@contesting.com]On Behalf Of Steve Katz
> > > > Sent: Tuesday, December 17, 2002 10:40 AM
> > > > To: 'Tom'; towertalk@contesting.com
> > > > Subject: RE: [Towertalk] Coax
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > > I am getting ready to replace some 10 year old coax and was
> > wondering
> > > > > what the coax, not hardline, of choice is for HF now. It will be
> > > > feeding
> > > > > a 2 element
> > > > > 5 band cubical quad with a capability of 1500 watts.
> > > > >
> > > > [Steve Katz] You didn't say how long that cable was going to
> > be, or
> > > > what is supporting the quad. The best choices for transmission line
> > > > usually
> > > > take into account the frequency of operation, line length and
> > operating
> > > > environment, e.g., fixed or crank-up tower; if any of the line will be
> > > > buried; if any of the line will be inaccessible for service; etc.
> > > > Example:
> > > > For longer runs, my first choice is RG17A/U since it's very strong,
> > very
> > > > low
> > > > loss and extremely easy to work with in all aspects except its rather
> > > > enormous weight. So, I don't use it on crank-ups (too heavy), but for
> > a
> > > > fixed, guyed tower it's pretty perfect, not to mention readily
> > available
> > > > for
> > > > a fraction of what the military pays for it. WB2WIK/6
> > > >
> > > >
> > > >
> > > >
> > > > > --
> > > > > 73,
> > > > >
> > > > > Tom mailto:trobertson@elp.rr.com
> > > > > KQ5S
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > AN Wireless Self Supporting Towers at discounted prices,
> > > > > See http://www.mscomputer.com
> > > > >
> > > > > Wireless Weather Stations now $349.95. Call Toll Free,
> > > > > 888-333-9041 for additional information.
> > > > > _______________________________________________
> > > > > Towertalk mailing list
> > > > > Towertalk@contesting.com
> > > > > http://lists.contesting.com/mailman/listinfo/towertalk
> > > > _______________________________________________
> > > > AN Wireless Self Supporting Towers at discounted prices,
> > > > See http://www.mscomputer.com
> > > >
> > > > Wireless Weather Stations now $349.95. Call Toll Free,
> > > > 888-333-9041 for additional information.
> > > > _______________________________________________
> > > > Towertalk mailing list
> > > > Towertalk@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/towertalk
> > > >
> > > _______________________________________________
> > > AN Wireless Self Supporting Towers at discounted prices,
> > > See http://www.mscomputer.com
> > >
> > > Wireless Weather Stations now $349.95. Call Toll Free,
> > > 888-333-9041 for additional information.
> > > _______________________________________________
> > > Towertalk mailing list
> > > Towertalk@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/towertalk
|