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Date: Thu, 02 Jun 2011 16:16:53 +0100
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Subject: Re: LF: Schumann
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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
>
>
>