Return-Path: Received: from mtain-mg03.r1000.mx.aol.com (mtain-mg03.r1000.mx.aol.com [172.29.96.203]) by air-de07.mail.aol.com (v127_r1.1) with ESMTP id MAILINDE072-5ebb4b8803503cb; Fri, 26 Feb 2010 12:22:24 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mg03.r1000.mx.aol.com (Internet Inbound) with ESMTP id B015C38000093; Fri, 26 Feb 2010 12:22:22 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Nl3sP-0007Bb-QE for rs_out_1@blacksheep.org; Fri, 26 Feb 2010 17:21:21 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Nl3sP-0007BS-0F for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 17:21:21 +0000 Received: from mail-bw0-f215.google.com ([209.85.218.215]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Nl3sL-0007Qm-N7 for rsgb_lf_group@blacksheep.org; Fri, 26 Feb 2010 17:21:20 +0000 Received: by bwz7 with SMTP id 7so280828bwz.4 for ; Fri, 26 Feb 2010 09:21:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=MO7VnfHd6/2pVO91IetBRzVJXcEXmTwrAEku2sHpues=; b=DmEanumGBanggh5om8P83h2FO5WABArW3Nnp3e5KO6iwbdm59L44Ib76OSIoYeXv/3 TCWuOdhOuOIZQBBcIy4gvb46WUGjo1jMHSR2P/m0OO5ev7WyZXxO89Qadauv7qTqqWNa 12ES3RFvqu/PexVACRzulBro8QhVLT04kkHs8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=ADeOUdyUUH4GtpGiOsl/yKk4+JhRh3go0R77KNaTomL2Ab4R/70D5p8RbpW/6dUlUX gTZAVf+8XqQotWJ4ZlpFQWnZRl3srDqutUK7nAJ6zh5SI9NME9YaD6wJSX4fqdXm3xY3 lixIJhLXqTsUo7kDQIXhNLDOY5Q4sRqXzMa1M= MIME-Version: 1.0 Received: by 10.204.131.85 with SMTP id w21mr462597bks.174.1267204869765; Fri, 26 Feb 2010 09:21:09 -0800 (PST) In-Reply-To: <9afca2641002260907k56b21a49p386d43b0be234436@mail.gmail.com> References: <931424D0B09442018D818E6AD1E5A63A@White> <9afca2641002260907k56b21a49p386d43b0be234436@mail.gmail.com> Date: Fri, 26 Feb 2010 17:21:09 +0000 Message-ID: From: Andy Talbot 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=0015173fe5bc1eba2704808420ca 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-d284.2 ; domain : googlemail.com DKIM : pass x-aol-sid: 3039ac1d60cb4b88034e735c X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --0015173fe5bc1eba2704808420ca Content-Type: text/plain; charset=ISO-8859-1 WSPR looks at the energy in 1.5Hz bins, or chunks, and effectively filters the signal to this bandwidth. If the noise impulses ar eof significantly shorter duration, they will be smeared outas well as reduced i magnitude and probably end up appearing quite close to Gaussian. Certainly, on 73kHz the impulsive Loran interference and natural spikes appeared completely Gaussian when filtered to the sub-Hz bandwidth we used there. However, for 9kHz signalling, I think you would do a lot better by going for coherent signalling. The path should be very stable so you shoul dbe able to retian coherency for hours. Use GPS timing and at that frequency you can get an absolutely coherent local reference and timing, so try long duration PSK, with symbol timings based on ten second intervals, or minutes. Andy www.g4jnt.com On 26 February 2010 17:07, Roger Lapthorn wrote: > *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 > --0015173fe5bc1eba2704808420ca Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
WSPR looks at the energy in 1.5Hz bins, or chunks, and effectively fi= lters the signal to this bandwidth.=A0=A0 If the noise impulses ar eof sig= nificantly shorter duration, they will be smeared outas well as reduced i= magnitude and probably end up appearing quite close to Gaussian.=A0=A0=A0= =A0 Certainly, on 73kHz the impulsive Loran interference and natural spike= s appeared completely Gaussian when filtered to the sub-Hz bandwidth we us= ed there.=A0
=A0
However, for 9kHz signalling, I think you would do a lot better by go= ing for coherent signalling.=A0The path=A0should be very stable so you sho= ul dbe able to retian coherency for hours.=A0Use GPS timing and at that fr= equency you can get an absolutely coherent local reference and timing, so= try long duration PSK, with symbol timings based on ten second intervals,= or minutes.
=A0
On 26 February 2010 17:07, Roger Lapthorn <rogerlapthorn@= gmail.com> wrote:
Two questions...
(1) Does anyone know how modes like WSPR behave with signals buried de= ep 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. Pe= rhaps there are certain modulation types that are well suited to get throu= gh for this sort of impulsive noise? I am no expert so have no idea but wo= uld value the views of people like Andy.

(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 2010 19:51, Alexander S. Yurkov= <fitec@omskcity.com> wrote:
> Subject: LF: Re: 9kHz noise level
>
> Dear LF,
>
> sometime back in 2000 I attempted to me= asure 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 assu= ming that it would depend only little on frequency. Using good old Spectro= gram with moderate averaging and placing the cursor between the visible im= pulsive spherics, I arrived at a background noise of about 5 dBuV/m refere= nced to 1 Hz (equivalent to 142 dB kTo).

Seems noise level depend strong on the location. Anyway it is ob= vious 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 theoryassumed 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 theoretica= l:-) 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

--0015173fe5bc1eba2704808420ca--