[Elecraft] K2/100 power-out change

[W3FPR - Don Wilhelm]

Rich, Dave, and all,

This is 'usual' behavior for the K2 - it seems the power shifts by about 5 
watts in high power mode.  It is present, but not noticable in low power 
mode because the shift is only about half a watt which is a smaller 
percentage of the power setting.

Checking the schematic, it seems this is controlled by the VPWR signal which 
is an output from the 8 bit DAC.  It would seem to me that each DAC step 
should be about 0.5 watts (128 watts/256 steps), so even with a DAC 
uncertainty of +/- 1, the power should vary by only 1.5 watts assuming that 
the DAC input value is held constant (I don't think that is possible).  My 
guess is that there is an additional uncertainty in the firmware calculation 
of the power to be transmitted that causes the remaining part of the 
variation.  The present region of uncertainty appears to be +/- 5 DAC steps 
if my math is anywhere close to correct.

Perhaps Wayne can comment and tell us if the firmware loop can be tightened 
a bit to reduce this power varaiation.  I don't drive an amplifier, but for 
someone who is driving an amp with say 50 watts from the KPA100, the real 
varaiation is 10% and for a 1500 watt amp, the final output variation is 
about 150 watts!!!

I really can't see this as a problem in actual operating practice (there is 
little difference in transmitted signal between 1350 watts and 1500 watts), 
but it can make meters 'dance' which may be quite disconcerting.

73,
Don W3FPR

----- Original Message ----- 

> Sounds like both K2's I have had. 38xx and 44xx. The output jumps all over 
> the place. My amp does not like it either. When I posted about it, the 
> response I got was that is "normal".
>