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[AMPS] Cantenna Dummy loads

To: <>
Subject: [AMPS] Cantenna Dummy loads
From: (John Fielding)
Date: Wed, 3 Feb 1999 17:02:37 +0200
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
easily achieved.

John    ZS5JF
> From: Rich Measures <>
> To:
> Subject: Re: [AMPS] Cantenna Dummy loads
To: <>
> 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
able to 
> 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
> Rich...
> R. L. Measures, 805-386-3734, AG6K,  
> --
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