|[AMRadio] Dummy Load|
k4kyv at charter.net
Mon May 19 13:08:18 EDT 2008
>>I made a mistake about 35 years ago buying some "non-inductive resistors
>>for a dummy load. The only place they were non-inductive was at 60 Hz. The
>>carborundums are not in the category.
>> Joe W4AAB
I use a bank of a dozen 600-ohm 150w "Glo-bar" carborundum resistors to
achieve a 50-ohm dummy load rated 1800 watts continuous duty air-cooled.
I once picked up some so-called noninductive resistors that were wirewound
in two layers wired in parallel, with the wire of one layer wound in
opposite direction of the other layer. They would not work in a dummy load
without a series variable capacitor to tune out the reactance. I suspect
that type of resistor, which may be satisfactory for the AM broadcast, might
have substantial inductive reactance on the HF amateur bands. With the
capacitor, mine worked OK. I doubt if an ordinary wirewound resistor could
be made to work satisfactorily, since it would behave more like an rf choke
than a resistor at those frequencies.
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