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[195.171.43.25]) by mx.google.com with ESMTP id ed13si1788927wic.105.2014.04.26.23.42.19 for ; Sat, 26 Apr 2014 23:42:20 -0700 (PDT) Received-SPF: none (google.com: owner-rsgb_lf_group@blacksheep.org does not designate permitted sender hosts) client-ip=195.171.43.25; Authentication-Results: mx.google.com; spf=neutral (google.com: owner-rsgb_lf_group@blacksheep.org does not designate permitted sender hosts) smtp.mail=owner-rsgb_lf_group@blacksheep.org; dkim=pass header.i=@mx.aol.com; dmarc=pass (p=REJECT dis=NONE) header.from=aol.com Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1WeIQG-0003D8-If for rs_out_1@blacksheep.org; Sun, 27 Apr 2014 07:18:44 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1WeIQF-0003Cz-Qd for rsgb_lf_group@blacksheep.org; Sun, 27 Apr 2014 07:18:43 +0100 Received: from omr-d02.mx.aol.com ([205.188.109.194]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.82) (envelope-from ) id 1WeIQD-0003VU-Lm for rsgb_lf_group@blacksheep.org; Sun, 27 Apr 2014 07:18:42 +0100 Received: from mtaout-mcc01.mx.aol.com (mtaout-mcc01.mx.aol.com [172.26.253.77]) by omr-d02.mx.aol.com (Outbound Mail Relay) with ESMTP id 5E78A7000008A for ; Sun, 27 Apr 2014 02:18:39 -0400 (EDT) Received: from White (95-91-237-52-dynip.superkabel.de [95.91.237.52]) by mtaout-mcc01.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id D575C380000A5 for ; Sun, 27 Apr 2014 02:18:38 -0400 (EDT) Message-ID: <6A66C9BDC5664C13B6E10C039FA8193B@White> From: "Markus Vester" To: References: <535C9006.5070404@virginbroadband.com.au> Date: Sun, 27 Apr 2014 08:18:37 +0200 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 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1398579519; bh=o4Nz3RoohvpnlAMmJWzs0igssCtYS9srDX6B6hCvMAM=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=x6bTjzjdkQq1o7E1xvgeFZ1lVGcc+37TtbBIWBzjrIsHeDk9ubnOMkD8sJz7v/g4h OOG1sge8WHMFixT3jkAoIapp6/ivor+OgZuFfxPBbC9VJ99FWkl9beie+AmcFCgMWy eUCRf5BvaixDHn6Y9M6rozaSxrxonE2nRrx589c0= x-aol-sid: 3039ac1afd4d535ca13e17ef X-AOL-IP: 95.91.237.52 X-Spam-Score: -0.6 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Hi Edgar, in principle, yes. But: The question is on how much improvement you would get, compared to a simple induction loop. A loop responds to the time derivative of the field, so doesn't respond to DC and very low frequencies. That's where sensors which respond to the field itself are needed (eg compass needles, Hall effect, fluxgates, NMR, squids). For example, the noise of a fluxgate is more or less flat with frequency, and there is a crossover frequency above which the simple loop wins (usually around 100 Hz, depending on factors like the size, copper mass, or ferrous core of the loop). [...] Content analysis details: (-0.6 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [205.188.109.194 listed in list.dnswl.org] 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (markusvester[at]aol.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.7 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: f7f918e40888a44a70dddae14bd6a529 Subject: Re: LF: Magnetometers Content-Type: multipart/alternative; boundary="----=_NextPart_000_0010_01CF61F1.4A1115C0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=HTML_30_40,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 Dies ist eine mehrteilige Nachricht im MIME-Format. ------=_NextPart_000_0010_01CF61F1.4A1115C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Edgar, in principle, yes. But: The question is on how much improvement you would get, compared to a = simple induction loop. A loop responds to the time derivative of the = field, so doesn't respond to DC and very low frequencies. That's where = sensors which respond to the field itself are needed (eg compass = needles, Hall effect, fluxgates, NMR, squids). For example, the noise of = a fluxgate is more or less flat with frequency, and there is a crossover = frequency above which the simple loop wins (usually around 100 Hz, = depending on factors like the size, copper mass, or ferrous core of the = loop).=20 A proton NMR magnetometer with a large enough sample is sensitive at DC, = and has the additional advantage of absolute calibration referenced to = the NMR Larmor frequency. But it actually responds to the integral of = the field, so SNR falls off more rapidly at with frequency.=20 Superconducting quantum interference devices (squids) have been used as = very low noise magnetometers up to a several 100 kHz. But this makes = sensse only in a shielded room. In the open, atmospheric background = noise dominates by orders of magnitude, and a copper coil of less than a = square meter is able to provides ample SNR at VLF. Narrowband resonant = matching doesn't improve the SNR from the coil itself (induction voltage = vs resistive noise), but it helps to bring down the noise contribution = from the attached preamplifier. Best 73, Markus From: edgar=20 Sent: Sunday, April 27, 2014 7:05 AM To: rsgb_lf_group@blacksheep.org=20 Subject: LF: Magnetometers Possibly a silly question but, Is it possible to detect low frequency electromagnetic waves with=20 Fluxgate or Proton Magnetometer? e.g. waves with frequency of 8 kHz to 29 kHz? Regards, Edgar Moonah, Tasmania. ------=_NextPart_000_0010_01CF61F1.4A1115C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Edgar,
 
in principle, yes. But:
 
The question is on how much = improvement you=20 would get, compared to a simple induction loop. A loop responds to the = time=20 derivative of the field, so doesn't respond to DC and very low = frequencies. That's where sensors which respond to the field itself = are=20 needed (eg compass needles, Hall effect, fluxgates, NMR, squids). For = example,=20 the noise of a fluxgate is more or less flat with frequency, and = there is a=20 crossover frequency above which the simple loop wins (usually = around 100=20 Hz, depending on factors like the size, copper mass, or ferrous=20 core of the loop).
 
A proton NMR magnetometer with a large = enough=20 sample is sensitive at DC, and has the additional advantage of = absolute=20 calibration referenced to the NMR Larmor frequency. But it actually = responds to=20 the integral of the field, so SNR falls off more rapidly at with = frequency.=20
 
Superconducting quantum interference = devices=20 (squids) have been used as very low noise magnetometers up to a several = 100 kHz.=20 But this makes sensse only in a shielded room. In the open, atmospheric=20 background noise dominates by orders of magnitude, and a copper coil of = less=20 than a square meter is able to provides ample SNR at=20 VLF. Narrowband resonant matching doesn't improve the SNR from the = coil=20 itself (induction voltage vs resistive noise), but it helps = to bring=20 down the noise contribution from the attached = preamplifier.
 
Best 73,
Markus
 

From: edgar
Sent: Sunday, April 27, 2014 7:05 AM
Subject: LF: Magnetometers

Possibly a silly question but,

Is it possible to = detect=20 low frequency electromagnetic waves with
Fluxgate or Proton=20 Magnetometer?

e.g. waves with frequency of 8 kHz to 29=20 kHz?

Regards, Edgar
Moonah, Tasmania.

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