[Elecraft] KPA-1500 Power Output Variation

[Jim McCook]

Some asked that I post results for the variable power output problem.  I 
now have a pretty good idea why output varies from 1350w to over 1700w 
at a given temperature with a fixed drive level between 7.000 and 
7.050.  The problem occurs only on 40m.  The antenna SWR varies from 1.4 
on 7.000 to 1.3 at 7.050, and 1.1 in the middle around 7.025 or 7.030.

Eventually, using the Utility, I discovered I could get very constant 
output by eliminating all tuner memories, then picking single Xl or Xc 
values _every 10 KHz_.  Values ranged from Xl = 480 at 7.000 to Xc = 121 
at 7.050, with other values in between.  That seems to be a big 
variation.  In any case, the values produced the right results when 
changed _every 10 KHz_.

Percentage change in SWR value over this relatively narrow frequency 
range is high compared to my other antennas.  I assumed memorizing those 
reactance values would solve the problem, but the tuner will only 
remember values within 20 KHz bins.  In other words, it would memorize 
only every other value.  That doesn't help.

On 160 and 80m the bins are 10 KHz wide.  On most other bands they are 
20 KHz wide, and on 10m they are 100 KHz wide.  I think narrow 
bandwidths of 40m antennas is common, so I'm hoping to see a change in 
the tuner's 40m tuner bin width to 10 KHz.

Jim W6YA