[Elecraft] New KX1 low power and 20m oscillation

[Don Wilhelm]

Stan,

I was not available yesterday, so could not respond to your initial post.
The problem is most likely in the Low Pass Filter, so count the turns on 
L1 and L2 very carefully - count the number of times the wire passes 
through the center of the core.  Double check the capacitors in the LPF 
for correct values.

You might want to check the current draw during transmit.  Assume the PA 
transistor should be 50% efficient and there is another 100 ma being 
used by the DDS and other circuits, 2 watts should require a total on 
500 ma.  If the current draw is greater than that, the Low Pass Filter 
has a problem and is shunting some of the power to ground.  OTOH, if the 
current is commensurate with the power produced then the solution will 
be found in the Q4 Q5 circuits or the DDS.

Going back to your earlier conclusion that there were oscillations - 
yes, that can happen and can give erroneous power indications.  If you 
were to look at the output on a scope and find the RF waveform looks 
"modulated", you can be certain the LPF is not suppressing the harmonics.

73,
Don W3FPR

On 5/6/2012 6:29 PM, Stan Gibbs wrote:
> I may have been a bit hasty in concluding that there were oscillations on
> 20m; after I disconnected my K3's 20m antenna, the 20m signal looks fine.
> So I may have just been overloading the K3's front end.  Not sure why the
> 40m signal didn't suffer the same issue, though.
>
> Still have a very low power output (1.7W 40m, 2.0W 20m) and I've done all
> the suggested troubleshooting in the manual.  Components all look in their
> proper places and well soldered.
>