Dummy loads

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From: Alvin G. Gann (jgann@mindspring.com)
Date: Thu Jun 06 1996 - 18:20:23 EDT


Recently Stan, VE7SKT, posted a message about a Radio Shack 50 ohm resistor.
Today I was in my local friendly Radio Shack and bought a card of two 100
ohm, 10 w. wire wound resistors, RS 271-135. Using my DVM, I measured them
for resistance. One is 100.5 ohms, the other 101.7 ohms. The parallelled
value is 50.5, calculated and measured. Then I measured the inductance of
each. In the same order they are 40.1 uhy and 41.4 uhy. The parallelled
value measured
16.3 uhy. The calculated value would be 20.4 uhy, but I put them close
together and measured at the half way point on each lead using a Sencor
Z-meter digital LC meter. I don't remember what frequency that puppy uses
but I seem to remember it is high AF, several 10's of KHz. Interestingly, I
got no difference from either relative orientation, saying that there is no
mutual inductance.

As to using this as a dummy load, the measured 16.3 uhy gives an inductive
reactance of 721 ohms at 7.04 and 1036 ohms at 10.115. I haven't assembled
it to check if the measured VSWR is in agreement with those calculations or
not. I'm presenting the raw data (not statistically significant because of
the sample size of 2) and will allow you to judge for yourselves whether
this would make a useful dummy load. It would certainly be big enough to
check any QRP rig in a brick on the key test.

72 --Jerry W1UI


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