Return-Path: Received: from mtain-mh09.r1000.mx.aol.com (mtain-mh09.r1000.mx.aol.com [172.29.96.221]) by air-da01.mail.aol.com (v127_r1.1) with ESMTP id MAILINDA012-86114b86fd7715f; Thu, 25 Feb 2010 17:45:11 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mh09.r1000.mx.aol.com (Internet Inbound) with ESMTP id 042BF3800008F; Thu, 25 Feb 2010 17:45:09 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NkmQw-00006b-5P for rs_out_1@blacksheep.org; Thu, 25 Feb 2010 22:43:50 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NkmQv-00006S-KT for rsgb_lf_group@blacksheep.org; Thu, 25 Feb 2010 22:43:49 +0000 Received: from imr-db02.mx.aol.com ([205.188.91.96]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NkmQs-0000eE-UF for rsgb_lf_group@blacksheep.org; Thu, 25 Feb 2010 22:43:49 +0000 Received: from mtaout-mb05.r1000.mx.aol.com (mtaout-mb05.r1000.mx.aol.com [172.29.41.69]) by imr-db02.mx.aol.com (8.14.1/8.14.1) with ESMTP id o1PMhY7a027967 for ; Thu, 25 Feb 2010 17:43:34 -0500 Received: from White (g229121046.adsl.alicedsl.de [92.229.121.46]) by mtaout-mb05.r1000.mx.aol.com (WebSuites/MUA Thirdparty client Interface) with ESMTPA id 3086EE0000E5 for ; Thu, 25 Feb 2010 17:43:31 -0500 (EST) Message-ID: <931424D0B09442018D818E6AD1E5A63A@White> From: "Markus Vester" To: References: <38A51B74B884D74083D7950AD0DD85E82A1B18@File-Server-HST.hst.e-technik.tu-darmstadt.de> <70718ADC6A924E2F9BA6C5F1294DAD14@JimPC> Date: Thu, 25 Feb 2010 23:43:29 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 12.0.1606 X-MimeOLE: Produced By Microsoft MimeOLE V12.0.1606 x-aol-global-disposition: G x-aol-sid: 3039ac1d29454b86fd137341 X-Spam-Score: 1.2 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RCVD_IN_SORBS_WEB=1.236 Subject: LF: Re: 9kHz noise level Content-Type: multipart/alternative; boundary="----=_NextPart_000_003D_01CAB674.553775C0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30,HTML_MESSAGE, MISSING_OUTLOOK_NAME 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-sid: 3039ac1d60dd4b86fd756eab X-AOL-IP: 193.82.116.20 ------=_NextPart_000_003D_01CAB674.553775C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear LF, sometime back in 2000 I attempted to measure the daytime noise backgro= und 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 wit= h moderate averaging and placing the cursor between the visible impuls= ive spherics, I arrived at a background noise of about 5 dBuV/m refere= nced to 1 Hz (equivalent to 142 dB kTo). This seems lower than most of the figures quoted recently, including= Jim's measurement. There may have been some issues with my calibratio= n, but I don't think my figure would have been off by tens of dBs. Any= way I will try to repeat the measurement this weekend. Part of the dis= crepancy could be that published figures inevitably include the energy= of the distict spherics, which may well contribute the dominant part= of the average noise power. Empiricaly I found that some noise limiti= ng or blanking was essential to maximize SNR for narrow bandwidth rece= ption. Based on this figure for noise, a first calculation for Stefan's 100= m kite antenna predicted a reception range well over 200 km,. using= QRSS-30 at 21 mHz! So the dreamers may be in for a nice sunday surpri= se... Best 73, Markus (DF6NM) From: James Moritz=20 Sent: Thursday, February 25, 2010 7:50 PM To: rsgb_lf_group@blacksheep.org=20 Subject: LF: Re: 9kHz noise level Dear LF Group, As a quick experiment to estimate noise level at 9kHz, I coupled a sig= gen=20 into my broadband RX loop antenna using a "current transformer in reve= rse"=20 arrangement to induce a known EMF into the loop. I used Spectrum Lab= to=20 monitor the RX output, set up for QRSS3 reception (0.46Hz noise bandwi= dth).=20 I reduced the signal level to give what I imagine would be an "M" copy= =20 trace, and from the induced EMF and loop area worked out the equivalen= t=20 field strength - this was 35uV/m. It is a bit difficult to say what th= e SNR=20 is, due to the constantly varying impulsive noise, but 6dB is probably= not a=20 million miles from the mark, which would imply a noise field strength= about=20 25uV/m per sqrtHz. I don't know if the noise level on VLF this evening= is=20 particularly high or low. The Alpha beacons are clearly audible here. Cheers, Jim Moritz 73 de M0BMU ----- Original Message -----=20 From: "Andy Talbot" To: Sent: Thursday, February 25, 2010 11:22 AM Subject: Re: LF: AW: 9 Dreamers > To get the V/m value from this, first calculate the effective area= of a=20 > 9kHz > isotropic antenna : > At 9kHz, lambda =3D 33333m, G =3D 4.pi.A/lambda^2, G =3D 1, so= A =3D > 88*10^6 m^2 > > 1mW of noise per Hz bandwidth, received in this aperture means noise= =20 > density > Nd =3D is 1.1E-11 W/m^2 > Field strength E volts/metre, =3D=3D SQRT(Nd. 377) > =3D 65uV/m in 1 Hz bandwidth, or 65uV/ (ROOT Hz) > ------=_NextPart_000_003D_01CAB674.553775C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Dear LF,
 
sometime back in 2000 I attempted to= measure the=20 daytime noise background at 9 kHz (see http://www.qru.de/vlf-theori= e.html).=20 I was using my regular LF antenna at my suburban QTH. The effecti= ve height=20 is ~ 9 m, calibrated on LF by comparison to a small loop,=20 and assuming that it would depend only little on= =20 frequency. Using good old Spectrogram with moderate averaging and= placing=20 the cursor between the visible impulsive spherics, I arrived= at=20 a background noise of about 5 dBuV/m referenced to 1 Hz (equ= ivalent to=20 142 dB kTo).
 
This seems lower than most of the fig= ures quoted=20 recently, including Jim's measurement. There may have been some issues= with my=20 calibration, but I don't think my figure would have been off by= tens of=20 dBs. Anyway I will try to repeat the measurement this weekend. Part of the discrepancy could be th= at published figures=20 inevitably include the energy of the distict spherics, which= may well=20 contribute the dominant part of the average noise power. Empiricaly&nb= sp;I found=20 that some noise limiting or blanking was essential to maximi= ze SNR for=20 narrow bandwidth reception.
 
Based on this figure for noise, = a first=20 calculation for Stefan's 100 m kite antenna predicted a reception= range=20 well over 200 km,. using QRSS-30 at 21 mHz! So the dreamers&= nbsp;may=20 be in for a nice sunday surprise...
 
Best 73,
Markus (DF6NM)
 

Sent: Thursday, February 25, 2010 7:50 PM
Subject: LF: Re: 9kHz noise level
=
Dear LF Group,

As=20 a quick experiment to estimate noise level at 9kHz, I coupled a sig ge= n
into=20 my broadband RX loop antenna using a "current transformer in reverse"= =20
arrangement to induce a known EMF into the loop. I used Spectrum= Lab to=20
monitor the RX output, set up for QRSS3 reception (0.46Hz noise ba= ndwidth).=20
I reduced the signal level to give what I imagine would be an "M"= copy=20
trace, and from the induced EMF and loop area worked out the equiv= alent=20
field strength - this was 35uV/m. It is a bit difficult to say wha= t the SNR=20
is, due to the constantly varying impulsive noise, but 6dB is prob= ably not a=20
million miles from the mark, which would imply a noise field stren= gth about=20
25uV/m per sqrtHz. I don't know if the noise level on VLF this eve= ning is=20
particularly high or low. The Alpha beacons are clearly audible=20 here.

Cheers, Jim Moritz
73 de M0BMU




----= - Original=20 Message -----
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To:=20 <rsgb_lf_group@bl= acksheep.org>
Sent:=20 Thursday, February 25, 2010 11:22 AM
Subject: Re: LF: AW: 9=20 Dreamers


> To get the V/m value from this, first calcula= te the=20 effective area of a
> 9kHz
> isotropic antenna :
>= At 9kHz,=20 lambda =3D 33333m,   G =3D 4.pi.A/lambda^2,   G = =3D 1,  =20 so  A =3D
> 88*10^6  m^2
>
> 1mW of noise= per Hz=20 bandwidth, received in this aperture means noise
> density
&= gt; Nd =3D=20 is  1.1E-11 W/m^2
> Field strength E volts/metre, =3D=3D SQ= RT(Nd.=20 377)
> =3D 65uV/m in 1 Hz bandwidth,    or 65uV/= (ROOT=20 Hz)
>


------=_NextPart_000_003D_01CAB674.553775C0--