LF: 500kHz propagation

[Rik Strobbe <rik.strobbe@fys.kuleuven.be>]

Over the past days I monitored the G4JNT WSPR beacon 24/24.
During daytime I have a weak but consistent copy of Andy's signal, 
average -24dB with ups and down of some dB.
During nighttime the signal is -10dB on average, with the usual deep 
QSB (peaking -1dB, dips down to -20dB).
But the most interesting observation is that in the afternoon the 
first peaks (from -24dB up to -8dB) occur as early as 15:45 UTC.
This is almost 1 hour before sunset (16:37 UTC) and almost 1.5 hours 
before the D-layer (at mid point) goes into darkness.
73, Rik  ON7YD - OR7T