Paul,
That is the correct fix for the problem.
The K2 controls power using a control loop that includes the entire
transmit chain. The control loop is stable with the base K2, but when
the gain of the KPA100 is added, the control voltages can overshoot -
just how much depends on the gain of a particular K2/100 when operated
at the high power setting.
Since the transmit gain is usually greatest on 40 meters, you will
likely notice the problem more there, and it will be at its minimum on
10 meters where the gain is less. The exact gain will vary depending on
the particular component tolerance mix and the amount of careful
construction used when building the K2.
Increasing R98 will dampen the loop response, but be careful not to go
too high or th epower output on 10 meters may never get up as high as it
should. Decide how much you are willing to impact the 10 meter power
output and use the highest value resistor at R98 that still allows that
power on 10 meters.
Each K2 is different (because of slight differences in gain). Some will
adequately dampen the loop overshoot with the normal 270 ohms while
others can use a value as high as 1500 ohms at R98. Determine the best
value for your K2 by testing with a temporary pot as indicated in the
Power Control Mod instructions.
73,
Don W3FPR
IK1QHB wrote:
Hi folks
I have end to build the KPA100 few days ago but there's a problem to fix.
When drive my Titan 425 gold series with my K2/100 ( nø 5985) have unstable
power control ( 20, 21, 23, 24, 19 watts), the grid current and output power
jump up and down (tipically 800 to 1100w with 20w input) on every band,
specially on 40 and 80m.
When KPA100 is OFF i can see very little flutter on simple k2 at 5w... 0,1
0,2 watts of flutter on internal k2 wattmeter
Seems not Feedback problem or similar, my antenna is a GP and Ros is
perfect...
Have read the mods by elecraft:
http://www.elecraft.com/Apps/Power_Control_Mod.html
Let me know if somebody have fix the problem with this or other mods.
Many thanks in any case, 73 de
Paul IK1QHB
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