Got my nerves together and tested the YouLoop last night with the same settings as my magnetic loop.
Thankfully it was just okay (but still amazing for the price/performance/size).
But it turns out modern computer hardware is still awful at keeping time. I noticed that my PC had drifted almost 3s in the last day. That’s too much for FT8 to cope with and I could see WSJT-X missing strong signals.
Windows does have a NTP client to keep the time updated, but it clearly only expects a low amount of drift and by default only updates once a week.
You can check the difference between your local time and real time on Windows by running:
w32tm /stripchart /computer:time.windows.com /dataonly /samples:5
I’m running NetTime with a 30min resync to see how things improve tonight. Hope no one minds me hitting the NTP server 336 times more often that normal…
Clearly the real fix is to work out how to replace my PC’s awful crystal with a GPSDO…. Or just sync using a USB GPS dongle I guess.