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[Towertalk] Coax opinions

To: <towertalk@contesting.com>
Subject: [Towertalk] Coax opinions
From: stevek@jmr.com (Steve Katz)
Date: Wed, 7 Aug 2002 15:36:07 -0700
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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> 
> _____________________
> Wes Cosand, PhD
> 6299 Durham Rd; Rt 413
> PO Box 349
> Pipersville, PA 18947-0349
> Email: wz7i@arrl.net
> Phone: 215-766-3842
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