[Elecraft] K3 PSK31 threshold/ 10W amp duty cycle.

[Richard Ferch]

LS,

With respect to power in PSK, I'd be just as concerned about signal 
quality (IMD, splatter) as about the power handling capability of the 
finals. PSK is extremely sensitive to IMD.

Instantaneous peak power in PSK can be twice the average power. Even if 
the amplifier is within its thermal ratings at full power, if 
instantaneous peaks are clipped your transmitted signal will have 
increased IMD. Operating below half the rated power should be OK, but 
you might want to do some on-air IMD testing before routinely using 
powers above half the rated power in PSK.

RTTY is a different story. The main issue in RTTY is not IMD, it is 
keying transients. These are visible as peaks in the frequency spectrum 
separated by multiples of the 45 baud keying rate. In the limited 
testing I have been able to do, I have not noticed any sensitivity of 
RTTY keying transients to output power.

What I have seen, however, is that my K3's AFSK signal is cleaner than 
the FSK signal - it's not that the FSK signal is bad, just that the AFSK 
keying transient peaks are lower. I believe Chen W7AY has made similar 
observations.

73,
Rich VE3KI