K2/100 unstable power...
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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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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 > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Ciao Don
This evening have made the mod on my k2/100w.
Now r98 is 1000 ohm and on 10m have 90w, and on 40m the power
is more more steady.... 1w not more.
The Titan work properly now.
I'm very very happy...
Now totally american shack!!! K2, Omni V, and Titan 425
gold... also the antenna is a wonderful Butternut HF6V @5m with 15
radials!
Hope to meet u on air on 40 every week end on CW!
Many thanks for your support.
73 de IK1QHB Paul
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