Dear Stefan, LF Group,
I just thought my receiver isn't working correctly. I thought the xtal
does not start to oscillate due to the higher ambient temperatures in the
afternoon. But later i found that the band noise on MF is significantly
lower than in the evening, at least 20 dB.
As well as the natural band noise being lower at MF (I estimate the noise FS
is about 10dB lower), there is also not the constant presence of man-made
noise, such as Loran and DCF39 sidebands. So the spectrum around 500kHz does
sound much quieter, especially during daytime.
What do others know about the ground wave range in summer and in the
afternoon? When does the band open? Similar to LF?
As others have said, broadly similar to LF - sky wave is very weak until
darkness has arrived, so ground wave dominates daytime communication. Ground
wave signal levels seem to depend greatly on the type of ground at distances
more than 100km or so. For example I can easily hear G3KEV during the
daytime here, and the path from Hatfield to Scarborough is over flat,
high-conductivity ground down the east of England. But G4WGT and G0NBD, and
stations in Wales, are extremely weak in daylight at similar distances,
although they are quite strong after dark The ground path to these stations
is over hilly, lower conductivity ground.
Sky wave signals over fairly long distances show very deep fading over
periods of a few minutes - signal levels are usually constantly changing,
and I have often seen variation of over 30dB in one minute on beacon
signals. This can make QSOs difficult, with a signal that was R5 suddenly
disappearing completely and not even visible on the spectrogram. Over very
long distances, trans-atlantic for example, the fading seems less severe
although signals are usually quite weak and propagation is very variable.
For contacts around Europe, I would say 136k actually gives more reliable
signal levels, but for many stations 500k is easier because higher ERP can
be achieved with a small antenna, and noise levels are often lower.
Cheers, Jim Moritz
73 de M0BMU
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