> Subject: LF: Re: 9kHz noise level
>
> Dear LF,
>
> sometime back in 2000 I attempted to measure the daytime noise background at
> 9 kHz (see http://www.qru.de/vlf-theorie.html). I was using my regular LF
> antenna at my suburban QTH. The effective height is ~ 9 m, calibrated on LF
> by comparison to a small loop, and assuming that it would depend only little
> on frequency. Using good old Spectrogram with moderate averaging and placing
> the cursor between the visible impulsive spherics, I arrived at a background
> noise of about 5 dBuV/m referenced to 1 Hz (equivalent to 142 dB kTo).
Seems noise level depend strong on the location. Anyway it is obvious for
industrial noise.
> Empiricaly I found that some noise limiting or blanking was essential to
> maximize SNR for narrow bandwidth reception.
Theory confirm this empirical rule. Few years ago i do some a theoretical
study of optimal signal recieption in the condition of strong spherics
noise. Such a noise is substantialy nongaussian then conventional theory
assumed gaussian noise is not adequate. The study show conventional
filtering (or FFT, it is the same) is not optimal. To get optimal SNR one
should do some nonlinear processing before filtering. This processing is
very similar to limiting. There is some an article on the subject on my
web page www.qsl.net/ra9mb but unfortunely it is in russian. And it is
very theoretical:-) I wonder if such a processing really improove SNR on 9
kHz. Such a processing was realized in GLFER program as author told to me.
But i don't test it.
Regards,
Alexander/RA9MB
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