Return-Path: Received: from mtain-dc12.r1000.mx.aol.com (mtain-dc12.r1000.mx.aol.com [172.29.64.140]) by air-mf05.mail.aol.com (v129.4) with ESMTP id MAILINMF053-8beb4c3ebbf3ce; Thu, 15 Jul 2010 03:42:43 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-dc12.r1000.mx.aol.com (Internet Inbound) with ESMTP id 71EE738000095; Thu, 15 Jul 2010 03:42:41 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OZJ3c-00078A-7u for rs_out_1@blacksheep.org; Thu, 15 Jul 2010 08:40:36 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OZJ3b-000781-Lz for rsgb_lf_group@blacksheep.org; Thu, 15 Jul 2010 08:40:35 +0100 Received: from cavuit01.kulnet.kuleuven.be ([134.58.240.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OZJ3a-0000c9-Rl for rsgb_lf_group@blacksheep.org; Thu, 15 Jul 2010 08:40:35 +0100 Received: from smtps01.kuleuven.be (smtpshost01.kulnet.kuleuven.be [134.58.240.74]) by cavuit01.kulnet.kuleuven.be (Postfix) with ESMTP id D7EDA7B804E for ; Thu, 15 Jul 2010 09:40:26 +0200 (CEST) Received: from ICTS-S-HUB-N3.luna.kuleuven.be (icts-s-hub-n3.luna.kuleuven.be [10.112.9.13]) by smtps01.kuleuven.be (Postfix) with ESMTP id C8E4931E702 for ; Thu, 15 Jul 2010 09:40:26 +0200 (CEST) Received: from ICTS-S-EXC2-CA.luna.kuleuven.be ([10.112.11.13]) by ICTS-S-HUB-N3.luna.kuleuven.be ([10.112.9.13]) with mapi; Thu, 15 Jul 2010 09:40:26 +0200 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Date: Thu, 15 Jul 2010 09:40:27 +0200 Thread-Topic: RE: DLF passive received with earth antenna Thread-Index: AcsjrnaLRy4u4YhES42LDEgDuB//tgAP3BcY Message-ID: References: <4C363DCD.303@iup.uni-heidelberg.de>,<4C3650A1.6040104@iup.uni-heidelberg.de> ,<4C3DA75D.80407@iup.uni-heidelberg.de> ,<263121BD51374246B3F184A43B2E9619@JimPC> <4C3E27D4.3060407@iup.uni-heidelberg.de>, In-Reply-To: Accept-Language: nl-NL, nl-BE Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: nl-NL, nl-BE MIME-Version: 1.0 X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.9 (/) X-Spam-Report: autolearn=disabled,HTML_10_20=0.945,HTML_MESSAGE=0.001 Subject: LF: RE: RE: DLF passive received with earth antenna Content-Type: multipart/alternative; boundary="_000_BF4A524700075746A6467658DFC7102C51094D0E48ICTSSEXC2CAlu_" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=HTML_FONTCOLOR_BLUE, HTML_MESSAGE,TO_ADDRESS_EQ_REAL 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: 3039ac1d408c4c3ebbf13830 X-AOL-IP: 193.82.116.20 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --_000_BF4A524700075746A6467658DFC7102C51094D0E48ICTSSEXC2CAlu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear Jim, Stefan, LF group, BTW, if my guess of 5mV/m is correct, and the loop EMF is 44mV, the effect= ive loop area would be about 18000m^2... that sounds impressive, based on the antenna length (280m) the "hight" of= the loop would be 64m. At 9kHz the radiation resistance of a 18000 m^2 loop is a mere 8 micro-Ohm= , thus a current of 11A is needed to radiate 1mW. But as the penetration depth into the earth is inverse proportional to the= square root of the frequency the effective loop area at 9kHz might be 290= 00 m^2, increasing the radiation resistance to over 20 micro-Ohm. What mea= ns that 7A antenna current is need to get 1mW radiated. But even that would require many kW. 73, Rik ON7YD ________________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] namens James Moritz [james.moritz@btopenworld.com] Verzonden: donderdag 15 juli 2010 1:40 Aan: rsgb_lf_group@blacksheep.org Onderwerp: LF: RE: DLF passive received with earth antenna Dear Stefan, LF Group, Taking a guess at ERP of DHO38 as 100kW, the FS at 411km distance would be about 5mV/m (if ERP were only 10kW, FS would be 1.7mV/m, if it were 1MW, 17mV/m, so 5mV is probably not too many dB wrong). The EMF induced in a 1-turn, 1m^2 loop would be about 2.5uV. From your description yesterday, this should give a level on the SpecLab display of -9dB -(44mV/2.5uV)dB which is -94dB, so below your background noise level, as you discovered. The noise voltage of a TLC271 is typically 25nV/sqrtHz - this is a poor match for a low impedance source such as a single-turn loop, but even so= the signal level should be well above the noise. With 3Hz FFT resolution, op-a= mp noise might be 50 or 60nV, which would be about -127dB on the SpecLab scal= e according to your calibration. Therefore the op-amp is probably not the limiting factor here, it is more likely the sound card input is determinin= g the noise floor. So you need to increase the gain in front of the sound ca= rd by 30dB - 40dB to get a good SNR. You could do this by: -Increasing the number of turns in the loop - e.g. a 30 turn loop like I used for 9kHz reception, which would increase EMF by nearly 30dB (it would also increase Z of the loop by a factor of about 900, but at VLF this woul= d still be small compared to the op-amp Zin) -Put a step-up transformer between loop and op-amp - a 1:30 ratio would achieve a similar result to having a 30 turn loop. -Increase the gain of the op-amp stage. To get 30dB gain at 23.4kHz, a TLC271 has marginal gain-bandwidth product; an OP-27 would be better in th= is respect as well as lower noise. Or some combination of these things. But remember this will also increase the level of unwanted signals at the soundcard input - if you have any nearby broadcast stations, you might need to include low-pass filtering. BTW, if my guess of 5mV/m is correct, and the loop EMF is 44mV, the effective loop area would be about 18000m^2... Cheers, Jim Moritz 73 de M0BMU --_000_BF4A524700075746A6467658DFC7102C51094D0E48ICTSSEXC2CAlu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Dear Jim, Stefan, LF group,

BTW, if my guess of 5mV/m is correct, and the= loop EMF is 44mV, the effective loop area would be about 18000m^2...

that sounds impressive, based on the antenna length (280m) the "hight= " of the loop would be 64m.

At 9kHz the radiation resistance of a 18= 000 m^2 loop is a mere 8 micro-Ohm, thus a current of 11A is needed to rad= iate 1mW.

But as the penetration depth into= the earth is inverse proportional to the square root of the frequency the= effective loop area at 9kHz might be 29000 m^2, increasing the radiation= resistance to over 20 micro-Ohm. What means that 7A antenna current is need to get 1mW radiated.

But even that would require many kW.

 

73, Rik  ON7YD
________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] namens James Moritz [james.moritz@btopenworld.com]
Verzonden: donderdag 15 juli 2010 1:40
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: RE: DLF passive received with earth antenna

Dear Stefan, LF Group,

Taking a guess at ERP of DHO38 as 100kW, the FS at 411km distance would be=
about 5mV/m (if ERP were only 10kW, FS would be 1.7mV/m, if it were 1MW, 17mV/m, so 5mV is probably not too many dB wrong). The EMF induced in a 1-turn, 1m^2 loop would be about 2.5uV.  From your description yester= day,
this should give a level on the SpecLab display of -9dB -(44mV/2.5uV)dB which is -94dB, so below your background noise level, as you discovered.
The noise voltage of a TLC271 is typically 25nV/sqrtHz - this is a poor match for a low impedance source such as a single-turn loop, but even so= the
signal level should be well above the noise. With 3Hz FFT resolution, op-a= mp
noise might be 50 or 60nV, which would be about -127dB on the SpecLab scal= e
according to your calibration. Therefore the op-amp is probably not the limiting factor here, it is more likely the sound card input is determinin= g
the noise floor. So you need to increase the gain in front of the sound ca= rd
by 30dB  - 40dB to get a good SNR.

You could do this by:

-Increasing the number of turns in the loop - e.g. a 30 turn loop like I used for 9kHz reception, which would increase EMF by nearly 30dB (it would=
also increase Z of the loop by a factor of about 900, but at VLF this woul= d
still be small compared to the op-amp Zin)

-Put a step-up transformer between loop and op-amp - a 1:30 ratio would achieve a similar result to having a 30 turn loop.

-Increase the gain of the op-amp stage. To get 30dB gain at 23.4kHz, a
TLC271 has marginal gain-bandwidth product; an OP-27 would be better in th= is
respect as well as lower noise.

Or some combination of these things. But remember this will also increase<= br> the level of unwanted signals at the soundcard input - if you have any
nearby broadcast stations, you might need to include low-pass filtering.
BTW, if my guess of 5mV/m is correct, and the loop EMF is 44mV, the
effective loop area would be about 18000m^2...

Cheers, Jim Moritz
73 de M0BMU

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