Hi Wes,
I've used, and like to use, stuff like RG217, RG17, RG18, etc. Reason: Very
available as new mil surplus, handles lots of power, even mismatched; solid
dielectric will withstand tons of abuse including driving cars and trucks
over it, and it lasts a very, very, very long time. Drawback is weight,
which is a lot! I think RG17/RG18 is about a pound a foot, so 300' weighs a
lot. I wouldn't want to climb a tower with 300' coiled up over my shoulder,
but using a pulley and rope have hoisted long lengths of it up very tall
towers, not too much the worse for wear...
RG214/U isn't bad, either...double shielded, very tough stuff, and much
lighter -- but more loss, and for 300' at 28 MHz, I'd try for something a
bit larger.
73!
Steve, WB2WIK/6
> So Steve, what would you use for HF at 1500 watts if you had a run of 300
> feet?
>
> Thanks
>
> Wes, WZ7I
>
> At 17:29 08/07/02 , you wrote:
>
>
> Hi Kevin,
>
> I, too, have used tons of LMR400. Here's what happens with a cable
> tie:
>
> It would indeed be difficult to compress the dielectric so severely
> that it
> shorts out due to mechanical failure. I certainly agree with that.
> However, in my own home installation, here's what's happened, not
> just once,
> but repeately:
>
> -Cable tie the LMR400 to tower leg. No superhuman strength, or even
> tools,
> involved. Just pulling an 8" tie (like Panduit) snug, by hand.
> -Run 1500W through the cable (50 MHz) on a hot day.
> -LMR400 dielectric breaks down precisely at the cable tie point,
> creating at
> first intermittently high VSWR, then, ultimately, complete failure
> at that
> point.
> -Examination and dissection of the cable indicates brown/black
> charring at
> failure point, where cable tie was installed.
>
> Pretty self-evident. Mean Time To Failure: About five minutes,
> under
> conditions described.
>
> I can repeat this, any time you'd like to come visit and see!
>
> I've had other problems with LMR400, too. Those have been
> documented in
> various magazines over the years, but all are "transmitting"
> related, and
> related to using high power. Never had a problem in "receive only"
> applications.
>
> 73 de Steve, WB2WIK/6
>
>
>
> "If everything seems under control, you're just not going fast
> enough." -
> Mario Andretti
>
> > -----Original Message-----
> > From: Kevin Hemsley [SMTP:kev@ida.net]
> > Sent: Wednesday, August 07, 2002 9:35 AM
> > To: Towertalk@contesting.com
> > Subject: Re: [Towertalk] Coax opinions
> >
> > I like LMR400 and I have used LMR600 for a longer runs. I use
> buryflex up
> > the tower and for rotor loops.
> >
> > Steve Katz"<stevek@jmr.com wrote:
> >
> > > They cannot be cable-tied with metallic or nylon tie wraps; they
> > > cannot be securely clamped; they they should all be gently
> > > supported in several locations along a 150' run.
> >
> > This is the first that I have ever heard of not cable tying
> LMR400. LMR400
> > is pretty tough stuff. You would need an extremely tight cable tie
> to
> > crush
> > the dielectric. I'm not sure it's even possible to tighten a nylon
> cable
> > tie
> > enough to make a dent in LMR400. Most wire ties are not installed
> > bone-crushingly tight, so it would greatly surprise me if this
> were an
> > issue.
> >
> > We've installed tens of thousand of feet of LMR400 using cable
> ties and
> > I've
> > never seen a problem. I searched Google and the Times Microwave
> site and
> > couldn't find any mention of the limitations you list. Do you have
> a
> > reference that describes the problems associated with using wire
> ties with
> > LMR400 cable?
> >
> > Thanks,
> > Kevin.
> > ------------------------------------------------------
> > Kevin Hemsley
> > kev@ida.net
> > NF7J
> >
> >
> > _______________________________________________
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> > <http://www.mscomputer.com/>
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> _______________________________________________
> Self Supporting Towers, Wireless Weather Stations, see web site:
> <http://www.mscomputer.com/>
> Call 888-333-9041 to place your order, mention you saw this ad and
> take an additional 5 percent off
> any weather station price.
> _______________________________________________
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>
>
> _____________________
> Wes Cosand, PhD
> 6299 Durham Rd; Rt 413
> PO Box 349
> Pipersville, PA 18947-0349
> Email: wz7i@arrl.net
> Phone: 215-766-3842
> FAX: 215-766-3843
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