[Elecraft] Re K2/100 Flat Topping on 30m

[peter barville]

On Thu, 31 Oct 2002, Don Brown wrote:

> I don't know if this is your problem but I had this come up in the
> KPA100 field test to the one I built. If R26 is set too low 30 meters
> would draw a lot of current at high outputs. I was getting up around
> 25-30 amps at 100 watts out. Other bands were not as high this only
> affected 30 meters. If this is the case you may be overloading your
> power supply and the voltage is dropping. Have you monitored the
> supply while transmitting to see if it is well regulated. The R26
> problem was due to setting the power calibration at 5 watts rather
> than 50 or 100 watts. When setting the calibration that low it is easy
> to be off by a fair amount at 100 watts. R26 sets the ALC feedback so
> it can cause strange reactions if not calibrated properly.
> 
> Don Brown
> KD5NDB   


I don't think the calibration of R26 can be the issue here, otherwise
the problem would be noticeable on all bands, and not just 30m (see my
*original* post).

However, if the low pass filter is tending to filter out some of the
desired 30m RF (ie the filter is rolling off too low in frequency), then
the PA would have to draw more current in order to produce the same
amount of RF. This could well explain why you were seeing excessive
current drain specifically on 30m, and why I (and perhaps others?) see
evidence of the rig flat topping on 30m at power levels well below 100
watts.

I'd be interested to know if others can set up a two tone test on 30m
and look at the output on a monitor 'scope.
-- 
72, peter g3xjs