From: Claudio Pozzi <smtp01@email.it>
To: rsgb_lf_group@blacksheep.org
Date: Sun, 23 Apr 2017 16:14:44 +0200
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Subject: Re: VLF: Some natural signals
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On Sunday 23 April 2017 06:34:07 you wrote:
> Thanks Paul,
> 
> What a wonderful sound.
> 
> Unfortunate that bird's magnetic sensors donā€™t have the
> sensitivity/bandwidth for what you captured; they could perhaps tune their
> nav systems for reduced sensitivity to the disturbance that chorus
> indicates.
> 
> Do you know if anyone has made audio translations of the mHz to 1Hz
> ionospheric-TEC waves (which modulate signals in HF and other bands)?  I'm
> referring to what some folks call ULF waves, where ULF refers to a
> geophysical-community convention of roughly 1 mHz to 1 Hz.
> 
> Or if anyone has made audio translations of the mHz to Hz modulation that
> magnetic storms can impress on VLF signals?
> 
> 73, Jim AA5BW
> 

Hi Jim. 

Interesting question,but how can I made this audio translation?

The 10 mHz signal period (T=1/F) is 100 seconds. 

So if I modulate in frequency or in amplitude a 1000 Hz carrier what sound can 
I heard? 
And the sound of the translated frequency like SSB USB (1000+0,01 Hz) is 
indistinguishable from a 1000 Hz sound. 

A 10 mHz frequency signal must be at least 100 seconds long for one complete 
sinusoid. 
If it's shorter how can I measure the frequency? 
Can I assume that the missing part of signal is a sinusoid?

In my opinion VLF signals (lower than few Hz) are better analyzed in time 
domain, not in frequency domain.

If you listen a 3600 seconds recording of VLF sound reproduced high speed in 
3,6 seconds the sound should be interesting. But each "frequency" is 
multiplied by 1000.

The short wave AM broadcasting fading is an "amplitude modulation" with few 
tenths of Hz frequency (and some group delay distortion).

73 de Claudio IK2PII


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