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

To: <[email protected]>
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
>
>
>