Today I roughed up a cable to get on air with WSPR and the new KX3 via a Signalink USB.
Ground, PTT and audio are wired from the RJ45 plug to the TRRS 3.5mm plug, while speaker out goes to the SPKR socket on the back of the Signalink. If WSPR spots are anything to go by it seems to be working pretty well and on air my transmissions sound reasonable (no outlandish hum or anything).
Looking at the received WSPR signals, it seems that the KX3 drifts a little in frequency compared to the FT-817. Here's a screen shot using the KX3 after running for about 30 minutes:
Here's an old shot of reception with the ft-817:
However, after running for a few hours the KX3 looks much better:
It's now been a day of operation at 2W 10% transmit and I feel that the receive drift is pretty clear:
Ever helpful Wayne Burdick from Elecraft responded in the Yahoo forum to say "I'm experimenting with algorithms that reduce short-term drift." It seems like the issue is related to VFO temperature compensation so it's possible they might be able to slow the effect for narrow, slow, digital modes in a future firmware update.
I'm really loving the KX3, the latest firmware update gave us really good noise reduction, and I'm starting to think about selling off the FT-817 which is really redundant. My hesitation is that the ft-817 is kind of compact and robust compared to the KX3 which really needs a case to be carried without worrying about bashing a knob off.