[Elecraft] K2/100 - Power investigation

[Don Wilhelm]

David,

You are chasing your tail since you are trying to use all those 
wattmeters - they will all be different.
You say that you are using a wattmeter between the KPA100 and the KAT100 
- that in itself can lead to a variety of readings.  The only thing you 
can really trust is a good dummy load.  The DL1 is good.

Because of the scaling done in the KPA100 for the output of the 
wattmeter to the K2, you can calibrate it at low power.  Disconnect the 
power cable from the KPA100 and power only the base K2.  Now, you can 
use your DL1 dummy load and do the calibration at 10 watts (the power 
control is a lot easier to use with no PS connected to the KPA100).  Be 
certain your KPA100 wattmeter is balanced first (do that into a good 50 
ohm dummy load or it will not be correct - use your DL1).   Then set the 
KPA100 forward power pot so the K2 display matches the power calculated 
from the DL1/DMM reading.  You may have to make several trials to 
average things out, but once calibrated that way, your KPA100 wattmeter 
will have greater accuracy than the run of the mill wattmeters - and it 
will be accurate on both the low and high power scales.

If you do it right, you can judge the accuracy of those external 
wattmeters by comparing them to your KPA100.

You can expect some variation from band to band because the diodes are 
not entirely linear with frequency.  Pick one band and stick with it 
while doing the calibration.  Attempting to calibrate on several bands 
is an exercise in frustration.  I like to use 40 or 30 meters, but if 
your operation is mostly on 20 meters, then that may be a better choice 
for you.

If you are attempting to compare wattmeters  with a live antenna, 
remember that common mode current on the feedline can also have some 
influence, and the amount of influence may be vastly different from one 
meter to another - as I said, the only thing you can trust during these 
calibrations is a known dummy load.

73,
Don W3FPR

David Wilburn wrote:
> Ok, I got all kinds of numbers off of the DL1.  The Bird seems a touch 
> low, showing 80 - 100w across all bands.  Every time I measure it a 
> different way, I get different numbers.  Very frustrating.  The W1 
> quit after about 5 min.  The MFJ meter gives one reading, the Bird 
> another, using the DL1 and doing a calculation, goes crazy on 10&12m 
> but more stable, and once again different on others.  Friend is going 
> to loan me his Bird, think it is a 4309, and we will see what it 
> shows.  I have put the Bird between the K2 & the KAT100, and 
> transmitted and then ID'ed, and got the 80 - 100w.  Am I chasing my tail?
>
>
> Dave Wilburn
> K4DGW
> K2/100 - S/N 5982
>
>
>