for your reply & the FB link.
about 160 miles (250km) from the transmitter with about 125 miles (200km) sea
harmonic signal on 504kHz is visible with SpecLab for about 95% of the time but
the patterns I have described are random but appear to be controlled as the are
instantly on or off as if by human intervention.
start of the pattern usually is slightly tapered & the finish is a fan
shape as seen in the spliced images attached. The total time of this sequence
yesterday (one of two) was about 80 minutes with little variation of the
parallel pattern other than the start & end.
The transmitter is located about 30miles
NW of Dublin and is mainly a sea path down to my qth. The 2nd
harmonic presence seems to vary from time to time and does not depend on which
antenna I use, either pa0rdt or 20m top loaded vertical.
Gary,not sure how close to
the coast you are but maybe it is directly across the water from you.