[Elecraft] K2/100 output variation

[G3SJJ]

Yes I understand Don. I was using the TUNE effect to demonstrate what I see.

I performed the following test on 40m with my 2 element phased array 
connected and an SWR of 1:1. Keying with a series of dashes, K2 output 
power of 34 watts initially dropped to 26w then toggled between 26 and 
34, this translated to an output power of  435w and 561w. With slightly 
more drive it oscillated between 42 and 50w producing about 670 and 830. 
The changeover time between the two levels is between 1 and 2 seconds.  
I didn't want to continuing QRMing the band so declined to check at full 
bore! (it is about 780w and 1kW for each state)

Someone emailed me directly and said he had changed **R99** to 1.1K, so 
now I am not sure whether to change R98 or R99??

73 Chris G3SJJ




Don Wilhelm wrote:
> Chris,
>
> You cannot make a sound judgement using TUNE.  Evaluate the R98 value change
> with actual keying.  If you change bands or change the power level, it will
> take a few dot times to settle into the new power setting, that part of your
> observation is normal.
>
> The rest of the situation is due to the loop response of the ALC control
> loop (that controls the power output) - it is quite with only the base K2,
> but adding the KPA100 can cause the loop to overshoot and oscillate -
> increasing R98 reduces the time constant of the loop and reduces the
> overshoot.
>
> Monitor the output on 10 meters during determining the maximum value for
> R98 - too much resistance will reduce the maximum power output on the higher
> bands, and yes you can compromise if you are willing to accept the lower
> power on 10 meters.
>
> 73,
> Don W3FPR
>
>   
>> -----Original Message-----
>>
>> No, that didn't help, Stewart. With the 100 PA disconnected and 5 watts
>> requested, I see around 0.5 w difference in actual power and that
>> is stable.
>>
>> Having re-connected the 100 w pa to restore the K2/100 to the state I
>> would normally use it, I have put a scope on the output. With requested
>> power of 50w, in Tune the readout shows 29w immediately, dropping to 24,
>> 21 and 17w, it then toggles between 17 and 22w. I can see this stepping
>> on the waveform displayed  on my scope. It also explains what I was
>> seeing the other night. Since I was working pile-up style, the overs
>> would be short, so each time I went to transmit the power variation in
>> the K2 would also vary drive to the amp with the consequent output
>> variation of between 100 and 200 w from the amp.
>>
>> Chris G3SJJ
>>
>>     
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