Return-Path: Received: from mtain-mc11.r1000.mx.aol.com (mtain-mc11.r1000.mx.aol.com [172.29.96.83]) by air-de04.mail.aol.com (v127_r1.1) with ESMTP id MAILINDE043-5eb04b88005530f; Fri, 26 Feb 2010 12:09:41 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mc11.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9712238000429; Fri, 26 Feb 2010 12:09:39 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Nl3fU-00070T-4g for rs_out_1@blacksheep.org; Fri, 26 Feb 2010 17:08:00 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Nl3fT-00070K-F0 for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 17:07:59 +0000 Received: from mail-bw0-f215.google.com ([209.85.218.215]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Nl3fQ-0007JJ-Rf for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 17:07:59 +0000 Received: by bwz7 with SMTP id 7so269294bwz.4 for ; Fri, 26 Feb 2010 09:07:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=2LJH/oXK+lJQz7LCFlBNlRlchH7rtLGS5qjU746ybYY=; b=ewHixG/Z+qS/JpFL3IfK8s6TXR3yO2kSiMFhvQvvn2YjFSs0RmLX8FxIlGWiiSTF0I 3fAAK8tAp3vwzMmtw3Y8Zc8fm03C5kKw6wFHtvaevOXnZqrQgeFcOcIOHvRt6Syo1NaG TDEJvuglccd77frixTv1eY0OJCWZO66riE5JM= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=g3CieNmSpS3XtoWxdk/kAlGTUrzJYVi2dAW81UprOPXIawwgd6cv12rVMT1rnItkSX sigxr/890sUOa4D+ym9Y6KEp6Aa8iaHVlvCmIr80/gURX/R2qNEidMipMLuW4e+CPXJt u3W8RitF5QbZKrL4oQX6bgyWZ20RURZzf7k/A= MIME-Version: 1.0 Received: by 10.204.38.77 with SMTP id a13mr507654bke.26.1267204069741; Fri, 26 Feb 2010 09:07:49 -0800 (PST) In-Reply-To: References: <931424D0B09442018D818E6AD1E5A63A@White> Date: Fri, 26 Feb 2010 17:07:49 +0000 Message-ID: <9afca2641002260907k56b21a49p386d43b0be234436@mail.gmail.com> From: Roger Lapthorn To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: 9kHz noise level Content-Type: multipart/alternative; boundary=00032555a3166f5680048083f040 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m273.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d60534b88005341ad X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --00032555a3166f5680048083f040 Content-Type: text/plain; charset=ISO-8859-1 *Two questions...* (1) *Does anyone know how modes like WSPR behave with signals buried deep in impulsive noise like sferics?* It seems that most of the natural noise at <9kHz is of this nature. Man-made noise is another matter. Perhaps there are certain modulation types that are well suited to get through for this sort of impulsive noise? I am no expert so have no idea but would value the views of people like Andy. (2) *Regarding OFCOM and NoV permits for <9kHz is it not reasonable that they should have some overview of any transmissions (radiated, conducted or inducted) which could be sources of interference?* We all appreciate that the radiated energy will be tiny, but near-field signals can be a significant interference source and over a considerable (local) distance at these very low frequencies. A most basic example could be interference to telephone, inductive loop audio systems, hi-fi or even pipe tracing systems. If any interference did occur, OFCOM would have some leads for investigation. It is not as if they are charging for NoVs. 73s Roger G3XBM On 26 February 2010 19:51, Alexander S. Yurkov wrote: > > 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 > > > > > -- http://g3xbm-qrp.blogspot.com/ http://www.g3xbm.co.uk http://www.youtube.com/user/G3XBM G3XBM GQRP 1678 ISWL G11088 --00032555a3166f5680048083f040 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Two questions...

(1) Does anyone know how modes like WSPR= behave with signals buried deep in impulsive noise like sferics? It= seems that most of the natural noise at <9kHz is of this nature. Man-m= ade noise is another matter. Perhaps there are certain modulation types th= at are well suited to get through for this sort of impulsive noise? I am= no expert so have no idea but would value the views of people like Andy.<= br>
(2) Regarding OFCOM and NoV permits for <9kHz is it not reasonab= le that they should have some overview of any transmissions (radiat= ed, conducted or inducted) which could be sources of interference? We= all appreciate that the radiated energy will be tiny, but near-field sign= als can be a significant interference source and over a considerable (loca= l) distance at these very low frequencies. A most basic example could be= interference to telephone, inductive loop audio systems, hi-fi or even pi= pe tracing systems. If any interference did occur, OFCOM would have some= leads for investigation. It is not as if they are charging for NoVs.

73s
Roger G3XBM

On 26 February 20= 10 19:51, Alexander S. Yurkov <fitec@omskcity.com> wrote:
> Subject: LF: Re: 9kHz noise level
>
> Dear LF,
>
> sometime back in 2000 I attempted to measure the daytime noise backgr= ound at 9 kHz (see http://www.qru.de/vlf-theorie.html). I was using my regula= r 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 on= ly 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 obviou= s 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 theore= tical
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<= br> 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.ne= t/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







--

http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088
--00032555a3166f5680048083f040--