[Elecraft] [K2] poor IMD on barefoot K2, even at low power

[Don Wilhelm]

Oleg,

It sounds like you have most everything right, so you may indeed be 
getting a false indication.

A quick check on the PA transistors is to connect a dummy load, set the 
power control to maximum and press TUNE.  If you develop over 14 watts 
on 40 and 30 meters, then the PA transistors are likely working just 
fine, but if the actual maximum power is only 6 to 10 watts, then you 
can suspect a bad PA transistor.

You could be overloading the receiver - run the K2 into a dummy load and 
put a short wire on the receiver - adjust the wire length so you obtain 
an S-9 or less signal into the receiver.

As Julian mentioned, the IMD report on many PSK-31 applications is not 
to be trusted for absolute values, but it can still be used for relative 
comparisons.

You might want to check the output of your soundcard for "cleanliness" 
too.  A bit of distortion in the soundcard output would create a bad 
IMD, but the M-Audio soundcard is usually clean.

Try swapping the laptop and the desktop PCs to see if that makes any 
difference (drive the K2 from the laptop).

73,
Don W3FPR

dl0tuh wrote:
> Don, Julian, thank you for your replies!
>
> I forgot to mention - RTTY mode is activated and selected, SSBCr is 1:1.
> SSBA is 3.
>
> The real IMD value may be far from what DigiPan tells me, but I see a very
> well known picture - two solid lines on the waterfall for two main tones and
> several minors for intermodulation products when sending idle.
>
> I was not sure if the distortion happens in FT840 or PC on receiver side,
> but with an antenna I can see strong but clean signals on the air. I also
> used my SoftRock and recorded the PSK sound - same distorted picture.
>
> Can it be something very stupid, like one dead transistor (Q7 or Q8) in the
> PA?
>   
>