[Elecraft] K2/100 output power fluctuation

[Don Wilhelm]

Ken,

This is not a 'problem', but is a condition that does occur in some K2s.
The situation is that the K2 power control mechanism is a loop, and if 
the gain in the RF stages is high (the gain increases when the KPA100 
switches in), then the power control loop can oscillate with a period 
from a half second to 2 seconds.

The cure is to add damping to the control loop which will cause the loop 
oscillation to diminish more quickly.  The element to change is RF board 
R98.  Remove the KPA100 and operate only the base K2, then temporarily 
replace R98 with a variable resistor (about 2K should work fine).  
Adjust the pot to higher and higher resistances watching the power 
output on 10 meters.  When the 10 meter power begins to drop, that is 
about as far as you can go without impacting the power output on the 
higher bands - measure the resistance of the pot (after removing it) and 
use the next lower standard value resistor in place of the original R98.
This information can be found on the Elecraft website under Application 
Notes as "Optional K2 Power Control" or look at the direct link 
http://www.elecraft.com/Apps/Power_Control_Mod.html.

Your 'thumping' in the computer speakers indicate that you should get 
better shielded speakers (or shield the wires into and out of the computer).

73,
Don W3FPR

Ken, KA0W wrote:
> Hello! 
>
> I'm noticing a power output fluctuation of about 10w on an external Array Solutions digital wattmeter and on an analog wattmeter out of my K2/100 (sn 6384). 
>
> The load isn't changing, tried different dummies, coax, and antennas too. Past recent history of station - no load problems thru 1.5kw.
>  
> It is more of an output jump, up and down - continuously back and forth. A fast jump, near instant. Doesn't matter much about power setting, whether 30w or 100w. 
>  
> At the 10w level (PA not switched in) out fairly stable, no jump up and down jumping. 
>
>