On Wednesday 22 September 2004 23:53, Robin Szemeti wrote:
> 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 :)
http://www.johnsradio-uk.com/products.asp
Bird 8645 25kW self contained beast. Already a snip but expect 15-20% off if
you haggle with cash. In comparison with what you're testing, and the time
other methods eat up, it's so cheap.
I've no connections to them.
Steve
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