> 
> I checked the noise level again during the daytime, and the noise level was 
> about 6dB lower than last night, i.e. about 13uV/m per sqrtHz

Dear Jim,
with  such  a noise  Stefan's signal should be detectable in QRSS100 at
100 km. Seems to be worth if such noise level takes place every day and
every night. It is naturally to assume noise level has some seasonal and
some irregular variations. More data will be usefull.

Regards,
Alexander