Hello Marco
Thank you for your input, yes I was astounded to see them then confused
by the frequency differences. Maybe some captures on the web have been
calibrated to put the theoretical frequency spot on in the days before
we had the accuracy available now. I have to remember to calibrate my
sound card before taking measurements.
73 Eddie G3ZJO
On 02/06/2011 15:22, Marco IK1ODO -2 wrote:
The first Schumann resonance is not at (300000/40000)=7.5 Hz, but
higher, usually around 7.7-7.8 Hz.
I was astounded when I observed it for the first time about 12 years
ago and found that the frequency was "not right" !:-)
The reason is simple: our Earth is quite transparent at very low
frequencies, so the average circumference of the ionosphere-Earth
waveguide is shorter than 40000 km.
In other words, the center of the first Schumann resonance is below
your feet, at a deptht of approximately 300 km.
The second one is a little bit higher than 15 Hz, and progressively
the other come closer to harmonics of a 40000 km wavelenght; but since
the Q is low, it is dfficult to extimate the exact frequency.
Have a look at http://www.vlf.it/Schumann/schumann.htm.
Years ago there was a website from Stanford University reporting the
measured frequency of Schumann resonances vs. time. The frequency
changes because of day/night ionospheric height variations, and
beacuse of SIDs and other disturbances. Fascinating !
To receive them you need a very large coil, or a simple E field
receiver and a quiet location; feed the signal to an audio interface,
and run a spectrogram in average mode. Quite easy to say, but it takes
some ingenuity and work to extract an useable signal.
Renato IK1QFK has a live spectrogram covering from 0.1 Hz up, see
http://www.vlf.it/cumiana/livedata.html - today we have thunderstorms
in the area, and the signal is completely wiped out.
Vy 73 - Marco IK1ODO
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