Hello Jim, Uwe and group,

Yes of course an LF broadcaster can only be used as reference if he is quite close to your station. Groundwave propagation must be dominant throughout the observation period. But there is a way to find this out:
Use the TV sync as reference to observe the MSF or DCF77 carrier. Requires no hardware (except for a potentiometers to adjust the input signals to the receiver).  Input signals (into the longwave receiver) will be 4*15625 Hz and 60kHz, or 5*15625 Hz and 77.5 kHz. Fortunately, in both cases the signals fit in a standard 3kHz IF bandwidth.

This allows checking if the reference phase is stable enough  -  if you are lucky you'll never have to let the TV turned on overnight ;-). I will try this experiment soon and let you know the results.

Thanks Uwe for the signal gallery. From your QTH, you can be sure to receive Loran from Sylt via groundwave !

Regards,
 Wolf  DL4YHF.