Dear Robin,
I sure wish I kept a copy of the photo that was circulating around
Bechtel this past winter showing the result of a coax fire that started
at the base of a monopole and flared out through the coax ports
at the top. It looked like something you see in oil refineries....
Since we were putting in Multi-Carrier Power Amplifiers all over the
place,
and since there was a typo in the original SOW that specified "10KW
output power,"
I approached my boss and asked if one of the contractors turned the
output
adjustment screw past 8'oclock, and he turned white as a sheet........
(The kludges being deployed would go into alarm at 200 watts, but
what do managers know, they're only there for the tee shirt.)
Hal Mandel
W4HBM
On Wed, 22 Sep 2004 23:53:27 +0100 Robin Szemeti <robin@redpoint.org.uk>
writes:
> On Saturday 14 August 2004 17:01, Dr. David Kirkby wrote:
>
> > Do you have access to a large drum of coax, just capable of taking
> the
> > power? Then a long length of it would become lossy and so
> dissipate
> > the heat along its length. If you unwound it, it will do it. Don't
> > leave it wound up, as it will obviously overheat.
> >
> > I used to use a 500' real of RG/58 coax as my dummy load on 2m
> with a
> > pair of 4CX250Bs. That could melt after several minutes, so was a
> bit
> > too thin. But 50 feet would have been fine I am sure - the loss
> was so
> > high.
>
> hmmm ... just remember a pair of 4cx250s puts out at best 700w on
> 2m, this is
> a 20KW device ... a 3CX15000 ... think about the dissipation, in a
> lossy
> line it will be exponential .... so if 100m had say a 10db loss
> you'd lose
> roughly half the power in 30m, that 10kw in 30m ... or 300w per
> metre ... I'd
> think its life could be measured in seconds ... apart from that,
> RG8 would
> probably not even stand the voltages from 20Kw into 50R, so maybe a
> couple
> of dozen kilometres of LDF550 might do the trick?
>
> I think I'll continue the search for a load ... I now have a water
> chiller
> capable of handling up to 45kw, so a water cooled load is looking
> like an
> option :)
>
> --
> Robin Szemeti
>
> Redpoint Consulting Limited
> Real Solutions For A Virtual World
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>
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