LMR240 @ 150 MHz -> 3dB/100ft -> 0.03 dB in a foot. -> 0.7% in a foot..
1000W being carried, that's 7W being lost in a foot. I think you'd feel
that, if you had something to compare to.. your hand probably covers about
1/3 foot, so that's like holding a 2W heater in your hand (compare to a
small christmas tree bulb.. the C7 small bulbs used in nightlights are 7W,
and too hot to touch)
Isn't QRO fun??
(contemplate, if you will, what happens if a waveguide flange on the 400kW
(CW) S-band transmitter of the Deep Space Network isn't perfectly mated...
Even a return loss of 50 dB (VSWR <1.01:1) is still 4W reflected back, and
50dB is a very, very impressive match)
----- Original Message -----
From: "Pat Barthelow" <aa6eg@hotmail.com>
To: <jimlux@earthlink.net>; <towertalk@contesting.com>;
<john.brewer@us.schneider-electric.com>
Sent: Monday, February 21, 2005 3:18 PM
Subject: LMR-240 Ultraflex/Heat
> 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@hotmail.com
>
> >From: "Jim Lux" <jimlux@earthlink.net>
> >To: <towertalk@contesting.com>,<john.brewer@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@us.schneider-electric.com>
> >To: <towertalk@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
> >
> >
> >_______________________________________________
> >
> >See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> >Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> >questions and ask for Sherman, W2FLA.
> >
> >_______________________________________________
> >TowerTalk mailing list
> >TowerTalk@contesting.com
> >http://lists.contesting.com/mailman/listinfo/towertalk
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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