While calibrating my scope, dummy load and DVM when working on my KX1 spring
tune up, I checked my outputs on my K3.
I found that the scope showed over 45 VPP at 5 watts into my dummy load. The
MFJ showed over 5 watts output.
I then performed the Low-Power (5 W) Wattmeter Calibration.
I adjusted the CONFIG:WMTR LP entry to show 45 volts peak on my scope when
driving my 49.7 ohm homebrew dummy load.
The MFJ-989D now shows 5 watts exactly when I key down with the power set to
5 watts.
The High Power (50 W) Wattmeter Calibration did not need adjusting!
BTW, the DVM has a frequency counter and it and the K3 VFO agree at 3.500
and 7.055!
So, unless I am missing something I am ready to go back to my KX1 spring
tune up with out worry about bogus readings.
BTW, I am considering buying the Elecraft Dummy Load because of the low
price and the built in DVM power output test points!
My thinking is that since my DVM has a hold function for readings I could
take the DVM and the Elecraft dummy load to my roof and connect the dummy
load to the coax that feeds the antenna (a 40 meter dipole cut for 1.0 SWR
at 7.05 MHz for example) and connect the DVM to the dummy load test points.
Then go back to the shack, key down for 1 second and go back to the roof and
check the reading of the DVM. This should tell me if my cable has any loss
beyond spec. It is only a 75 foot run but it is very old coax. For the
record, the K3 shows a 1.0 SWR on this antenna at 100 watts. The MFJ Tuner
shows a 1.0 SWR at 500 watts.
I got the 1.0 SWR on the dipole by cutting and measuring until I got
resonance. I am wondering if the resonance I got could be because I matched
the coax and the antenna length not a true 50 ohm antenna to a 50 ohm
transmission line! There is also the question of loss in the coax because of
age. By checking the power at the end of the coax versus power at the tuner
I hoped to get an idea about what is really going on.
Am I chasing ghosts here? Feedback would be appreciated!!
BTW, this is an exercise in learning for me! Thanks to Don Wilhelm I have
already learned a shortcut way to calculate power! Square the p-p voltage
and divide by 400! I like these kinds of little math "tricks".
Thanks in advance
Jack AE6GC
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Mar 18, 2009; 10:30pm
