Water cooled dummy loads are commonly used in the broadcast transmitter
scene. I once visited Marconi in Chelmsford to do some acceptance
tests on a 100kW transmitter. In each bay where the transmitters were
assembled there was a power meter on the wall. Well, it didn't look
like a power meter at first sight. It consisted of a small metal
enclosure with pipes running in from the bottom and out of the top. It
measured about 1ft high and 6" wide. It had a thermometer in the inlet
and outlet pipes and a glass tube with a steel ball bearing which got
pushed up the graduated scale by the water flow. A large matrix chart
was pasted on the wall next to it.
To measure the power you first turned on the water by the stop-cocks
until the steel ball bearing sat about half-way up the tube, turned on
the transmitter and then read off the temperature difference between
the inlet and outlet thermometer. I was told that 10% accuracy was
> From: Rich Measures <firstname.lastname@example.org>
> To: email@example.com
> Subject: Re: [AMPS] Cantenna Dummy loads
> Date: 03 February 1999 06:50
> > The Cantenna dummy loads just can't take 1.5 Kw for
> >very long.
> Indeed. The resistor used typ. looks like an approx. 100w unit.
> Apparently the name "dummy load" refers to those who expect to be
> put 1.5kW of NØN (AØ, keydown) through it
> > I was wondering if anyone has tried to
> >cool one of these. Either by running water thru the
> >can in a coil of copper tubing or maybe even having
> >the water replace the oil and run it thru the can.
> Direct contact of the surface of the resistor with water (only during
> testing) might work, Bill. Water is the undoubtedly one of the best
> liquid coolants. // I bought a Bird Model 8730 10kW continuous
> 50-ohm termination (s/n 0295) that hooks up to a garden hose. The
> is surprizingly compact compared to conventional 10kW terminations.
> moving water passes over the surface of the 50-ohm resistor. The
> dielectric constant of the water figures in the Z match. When I'm
> testing an amp I connect a hose and sprinker to the water output
> and water the lawn. . . Now that my >1400w amps have been sold,
> need to find a new home for the 8730. A water flow meter and all of
> Bird paperwork is included. // Sprinkler Not included.
> - later
> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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