Having made up the audio cables for the KX3 it was time to try it on QRSS (slow speed morse). As Bill W4HBK was running his QRSS grabber on 40m Friday night it would be possible to see the on air signal. The following is a capture from Bill over a 6 minute period
The upper signal (N4FRE) is the GPS locked ARDMEPT. The lower DFCW signal (WW2R) is from KX3. Both signals have 4Hz frequency shift and are running 200mW The drift on Transmit noticable on the KX3 and a little unpredictable; the pattern between different (even adjacent transmit period) periods is not the same
The following shows a comparison between the two signals over a two hour period. Each transmission is repeated every 10 minutes, synchronised to GPS. The good news is that the long term stability is good, It doesnt drift too much over the period BUT the bad news is that the short term drift over a couple of minutes is not good enough for QRSS
Unlike the Elecraft K3 there is no provision to lock the KX3 to an external high stability oscillator. The KX3 uses the SI570 chip that is self contained. Looks like the KX3 will need a lock board for narrowband modes.