Message-ID: <003a01c3a89a$6d0fd550$b732f7c2@johnb5a82ea1a4>
From: "John Rabson" <word.factory@zetnet.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <19d.1ca91b53.2cdcf1ce@aol.com> <01ce01c3a895$53649500$ac2465d5@oemcomputer> <3FB150A2.1020407@virgin.net>
Date: Tue, 11 Nov 2003 21:26:01 -0000
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Subject: Re: LF: Re: Dummy loads at LF
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About 30 years ago, Ongar Radio station to the north-east of London had a
number of nine kilowatt HF ISB transmitters. For dummy loads they used
carbon tubes about a foot long and an inch or two in diameter. Resistance
was 75 ohms and they were cooled by pumping water through them. I had a box
of such resistors, but they went missing in a house move.

73
John Rabson G3PAI

----- Original Message ----- 
From: "Stewart Bryant" <stewart.bryant@virgin.net>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, November 11, 2003 9:12 PM
Subject: Re: LF: Re: Dummy loads at LF


> When I was a PhD student we used to make high power resistors
> to terminate very large pulse generators from PVC tube filled
> with copper sulphate and with brass end plugs. By varying the
> size of the resistor and the concentration of the copper sulphate
> we could get the value we wanted. I can't remember how powerful
> these generators were (not my project), but they ranged
> from the size of a small van to a very large lorry :)
>
> Interestingly the high frequency performance of these resistors
> was not a problem.
>
> A quick check on Google pointed me to this design info:
>
> http://www.kronjaeger.com/hv/hv/comp/res/
> (It's actually interesting to also look at the top level page)
>
> http://www.samtech.co.uk/PDF%20files/liquid%20res.pdf
>
> 73
>
> Stewart
>
> Johan Bodin wrote:
> > Dear group,
> >
> > at a wavelength of 2200m I can't see any reason why a bucket of
> > salt water can't be used as a "poor man's dummy load". Also,
> > water needs a lot of energy to heat up. At 4.18 kJ/(kg*K) a 10 liter
> > bucket will take a kWh, or so, before reaching the boiling point...
:-)
> >
> > By the way, the speed (frequency) control system at SAQ contains
> > servo controlled "liquid rheostats".
> >
> > Any ideas for electrode material?
> >
> > 73
> >
> > Johan SM6LKM
> >
> >
> >
>
>
>