[Towertalk] Coax opinions

[Steve Katz]

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
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