Posted by
Tony Scesny on
Oct 30, 2010; 12:08am
URL: http://elecraft.85.s1.nabble.com/K3-LPA-power-level-accuracy-tp5688027p5688419.html
Hi James:
Use the DL1 dummy load from Elecraft. Its a great diagnostic
tool. It has low inductive resistors 20 watts but will take 90 watts
for short periods. Its greatest feature IMHO is the terminals to
measure the RF voltage. It has much greater accuracy. Hook it
directly to the coax connector on the back of K3. For power settings
from 0-12 LP CONFIG:WTMTR will show LP and all power above that it
will show HP. Now [disp] will show the defaults of 70 for LP and 30
for HP. Set power for LP at 10 watts and the voltage reading should
be around 15.4 volts and 90 watts at 35.65 volts. Adjust LP or HP to
correct the voltage. The change won't be linear so watch it. After
changing the LP and HP re-run the 5 and 50 watt calibrations. As the 5
and 50 watt cals are running you can watch the resulting voltages as
each band changes. (5 watts is 10.9v and 50 watts is 35.65 v) for
reference. There may be a particular band you want greater accuracy, so
you may want to interpolate to get the best average, since it is NOT PER
BAND. My K3 showed LP of 70 was OK but I changed HP to 40 to get
greater accuracy at 90 watts.
Don Wilhelm corrected the formula listed in the DL1 sheet. Watts
= (Vdmm + Vdiode} ^2 / 25 where Vdiode is assumed to be 0.3 v.
73 and have fun Tony K2ZLS at optonline dot net
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