[TowerTalk] LMR-240 Ultraflex/Heat

[Pat Barthelow]

Jim does a good job with the details...
and raises a question....
Some 20 years ago at a Marconi FM broad cast band transmitter sharing the 
site of a local ham repeater, I happened to grab some RG 213 Jumpers in the 
the front of the transmitter rack panel.   They were carrying the (I 
believe) 1KW FM station's output.  They were noticeably warm when my palm 
was wrapped around them.  In general, when Ultraflex 240, RG-213,  or 
whatever, coax is carrying it's maximum average load, conitunous duty, on a 
flat swr line, Would a person feel the coax to be cool, warm, very warm or 
hot?  Any experience?
73,
Pat aa6eg at hotmail.com

>From: "Jim Lux" <jimlux at earthlink.net>
>To: <towertalk at contesting.com>,<john.brewer at us.schneider-electric.com>
>Subject: Re: [TowerTalk] LMR-240 Ultraflex
>Date: Mon, 21 Feb 2005 14:51:30 -0800
>
>Ooops, that was the peak power limit...
>The average power limit is much lower... Looking lower down on the data
>sheet...at 30MHz, they give 1.49 kW average.  Applying the same 6dB margin
>for mismatch, you're down to about 370W.
>
>The conditions at the bottom of the graph show 40C jacket, 100C
>innerconductor temp, VSWR 1.0:1, no bending, etc.
>
>So, it sort of depends on what you mean by "high power patch cables"... I
>wouldn't be comfortable running  a kilowatt through it with arbitrary loads
>and having it snaked around.
>
>Something to think about.. For very short cables with solid copper center
>conductors, the thermal path may be shorter longitudinally through the
>center conductor, where the thermal conductivity is high, as opposed to
>through the dielectric and jacket, where the thermal conductivity is orders
>of magnitude lower.
>
>When you buy semirigid microwave coax for cryogenic applications, you get
>stainless steel jacket and silver plated stainless steel center conductors,
>for just this reason.
>
>
>----- Original Message -----
>From: <john.brewer at us.schneider-electric.com>
>To: <towertalk at contesting.com>
>Sent: Monday, February 21, 2005 5:39 AM
>Subject: [TowerTalk] LMR-240 Ultraflex
>
>
> > I'm noting the power carrying capability and wondering if anyone's had 
>any
> > experience with this coax ( LMR240 ultraflex).
> >
> > Seems like it would be ideal for high power patch cables, since it's 
>much
> > more easily bent than larger (RG8/213) cable.
> >
> > I need to replace a 150 foot run, as well, and this cable seems 
>attractive
> > both from a price/spec standpoint.
> >
> > Are there any gotchas in its use?
> >
> > John K5MO
>
>
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