Hello Jim, Alan, G.., Laurence, Roelof, MF,
Thanks for the discussion and detailed informations. Many interesting
things to learn. That sounds all very exciting and confirms many of my
assumptions.
Hope to meet you soon on the band.
73, Stefan/DK7FC
Am 17.06.2012 22:06, schrieb James Moritz:
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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