Return-Path: Received: from mtain-ma06.r1000.mx.aol.com (mtain-ma06.r1000.mx.aol.com [172.29.96.14]) by air-df07.mail.aol.com (v129.4) with ESMTP id MAILINDF072-5efb4c474588d9; Wed, 21 Jul 2010 15:07:52 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-ma06.r1000.mx.aol.com (Internet Inbound) with ESMTP id A032038000044; Wed, 21 Jul 2010 15:07:49 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ObecP-0006zC-QP for rs_out_1@blacksheep.org; Wed, 21 Jul 2010 20:06:13 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ObecO-0006z3-Fy for rsgb_lf_group@blacksheep.org; Wed, 21 Jul 2010 20:06:12 +0100 Received: from imr-ma02.mx.aol.com ([64.12.206.40]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1ObecM-0001y1-Dk for rsgb_lf_group@blacksheep.org; Wed, 21 Jul 2010 20:06:12 +0100 Received: from imo-da03.mx.aol.com (imo-da03.mx.aol.com [205.188.169.201]) by imr-ma02.mx.aol.com (8.14.1/8.14.1) with ESMTP id o6LJ60dZ012504 for ; Wed, 21 Jul 2010 15:06:01 -0400 Received: from MarkusVester@aol.com by imo-da03.mx.aol.com (mail_out_v42.9.) id l.c9b.55942866 (45489) for ; Wed, 21 Jul 2010 15:05:56 -0400 (EDT) Received: from smtprly-db01.mx.aol.com (smtprly-db01.mx.aol.com [205.188.249.152]) by cia-mc07.mx.aol.com (v129.4) with ESMTP id MAILCIAMC074-5bc44c474509168; Wed, 21 Jul 2010 15:05:56 -0400 Received: from webmail-d086 (webmail-d086.sim.aol.com [205.188.181.41]) by smtprly-db01.mx.aol.com (v129.4) with ESMTP id MAILSMTPRLYDB013-5bc44c474509168; Wed, 21 Jul 2010 15:05:45 -0400 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> <3F71CB69-5F2E-4BEE-BB5E-651DA77CC39E@numeo.fr> <4C3F76CB.1020709@iup.uni-heidelberg.de> <4C40DAEB.3010500@iup.uni-heidelberg.de> <4C40DDE8.4070507@iup.uni-heidelberg.de> <01C3A2B647BB4AF099A4BC1947CF2E45@JimPC> To: rsgb_lf_group@blacksheep.org Date: Wed, 21 Jul 2010 15:05:44 -0400 In-Reply-To: <01C3A2B647BB4AF099A4BC1947CF2E45@JimPC> X-MB-Message-Source: WebUI MIME-Version: 1.0 From: Markus Vester X-MB-Message-Type: User X-Mailer: AOL Webmail 32213-STANDARD Received: from 194.138.39.52 by webmail-d086.sysops.aol.com (205.188.181.41) with HTTP (WebMailUI); Wed, 21 Jul 2010 15:05:44 -0400 Message-Id: <8CCF71EDB15163C-2268-2AD6@webmail-d086.sysops.aol.com> X-Spam-Flag:NO X-AOL-SENDER: MarkusVester@aol.com X-Spam-Score: 0.3 (/) X-Spam-Report: autolearn=disabled,FORGED_AOL_TAGS=0.281,HTML_MESSAGE=0.001,UNPARSEABLE_RELAY=0.001 Subject: VLF: RE: DLF passive received with earth antenna Content-Type: multipart/alternative; boundary="--------MB_8CCF71EDB1C3A62_2268_5E57_webmail-d086.sysops.aol.com" 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=FORGED_AOL_TAGS, HTML_FONTCOLOR_UNKNOWN,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-sid: 3039ac1d600e4c47458566bb X-AOL-IP: 193.82.116.20 X-AOL-SPF: domain : blacksheep.org SPF : temperror ----------MB_8CCF71EDB1C3A62_2268_5E57_webmail-d086.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Dear Stefan, Jim, LF, last weekend, I attempted a fieldstrength measurent of DHO38. I used a sm= all nonresonant loop (6 turns, 41 cm diameter, 0.792 m^2), directly connec= ted to the soundcard, without a preamp or buffer. With the "Mic" slider fu= lly up, full scale was 18.8 mV rms. The noise level (-98dB in 17.6 Hz =3D= 56.4 nV/sqrtHz) was low enough to measure the four strongest MSK signals. As Jim mentioned, the correction factor for thze MSK bandwidth depends on= bandwidth, and I spend some time calibrating this. Direct integration of= the spectral density across the 200 bd MSK spectrum resulted in an effect= ive bandwidth of 105 Hz. For Stefan's 2.93 Hz FFT (ie. 4.4 Hz noise bandw= idth due to Hann window), the bandwidth factor should theoretically be 20= .2 - 6.4 =3D 14.8 dB.=20 For simplicity, I read the levels from SpecLab's waterfall cursor. Long av= eraging (> 10 s scroll with Optimum Waterfall averaging) is required to mi= nimize the remaining raggedness of the spectrum. One should try to avoid= occasional times with apparent periodic patterns in the transmitted data,= leading to significant spectral peaks. An additional offset resulted from the parabolic peak estimation, which is= optimized for carriers, but tends to be 1.5 dB high for flat noise. So in= effect, Stefan would have to add 12.3 dB (rather than 14.8 or 11 dB) to= the cursor readout. For my measurements, I selected an 11.7 Hz FFT and ad= ded 6.3 dB. BTW There are probably better ways to read MSK levels from SpecLab, either= by using the new "pam().ampl" function, or simply selecting a large enoug= h resolution bandwidth (e.g. 187 Hz) to follow the signal modulation.=20 My results for DHO38 at 475.3 km range were -79.5 dB =3D 4.11 uV (Saturday night 23:30) -82.1 dB =3D 3.05 uV (Sunday daytime 10:15) With the effective height of the small loop=20 heff =3D A / (lambda/2pi) =3D 0.388 mm at 23.4 kHz (equivalent to Jim's formula), I get a fieldstrength of=20 10.6 mV/m =3D 80.5 dBuV/m (night), 7.86 mV/m =3D 77.9 dBuV/m (day). Here is a table containing also the fieldstrength measurements of three ot= her MSK stations: kHz dBuV/m Call km night day 45.9 68.3 56.1 (NSY) 1390, 23.4 80.5 77.9 (DHO) 475, 22.1 73.0 ~65.5 (GQD) 1155, 21.75 77.0 71.1 (HWU) 796. On the German blog http://www.mysnip.de/forum-archiv/thema/8773/109722/Superpulse+auf+19_6+kH= z.html someone who worked at DHO38 states that they have eight 100 kW transmitter= s, feeding an array of eight antennas. With 80% combined antenna efficienc= y, they can radiate 640 kW (EMRP). This would theoretically result in E =3D 84.1 dBuV/m here in Nuernberg. The difference to the measured values might be attibute= d to an ionospheric component, or ground loss, or simply to the fact that= they may not be regularly operating at full power. To apply my DHO measurement to Stefan's ground loop experiment in Heidelbe= rg, we would have to scale daytime fieldstrength from 475 to to 411 km, gi= ving=20 E =3D 9.1 mV/m at his site. The voltage at the antenna terminals was U =3D 44 mVpeak - 11dB + 12.3 dB =3D 36.1 mV rms. Thus the effective height of the 280 m long earth antenna was=20 heff =3D U/E =3D 3.97 m at 23.4 kHz, giving a the ground loop area=20 A =3D heff * lambda/2pi =3D 8090 m^2, and an effective return current depth d =3D heff /length =3D 29 m. This depth appears to be much less than half of the baseline length, so it= is probably indeed skin effect limited. Scaling the 23.4 kHz results to= 9 kHz would give 1.6 times more skin depth, but 1.6 times less effective= height (ie. 2.5 m) due to the larger wavelength to loop length ratio. Thu= s the transmit efficiency at 9 kHz would be about 26 dB less than that of= a 100 m kite antenna with similar loss resistance. Kind regards, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: James Moritz An: rsgb_lf_group@blacksheep.org Verschickt: Sa., 17. Jul. 2010, 23:43 Thema: LF: RE: DLF passive received with earth antenna Dear Stefan, LF Group,=20 =20 It gets confusing when the bandwidth changes! In this case, both measureme= nt bandwidths are much smaller than the modulation bandwidth, and the sign= al has a continuous spectrum, so it is reasonable to assume the measured= signal power will be proportional to the measurement bandwidth. The ampli= tude of the signal on the earth antenna was -20dB in 3Hz BW. To normalise= the measurements to a 3Hz FFT BW, you need to add 6dB to the amplitude of= the 1m^2 loop signal in 0.75Hz bandwidth, to give -94dB as you said. The= ratio of signal amplitudes is then 74dB, or a factor of about 5000. So th= e eqiuvalent area of the earth antenna is 5000m^2.=20 =20 Adding Markus' factor of 11dB to give the total signal amplitude from the= 1m^2 loop gives -83dB, 74 dB below your reference level of 44mV =3D -9dB.= Therefore the 1m^2 loop EMF is about 9uV, corresponding to FS of DHO38 be= ing about 18mV/m. If this is correct, it corresponds to about 1.1MW ERP,= which is impressive, but since the signal is down in the noise in your sy= stem, these figures can only be a very rough estimate.=20 =20 Cheers, Jim Moritz=20 73 de M0BMU=20 =20 ----- Original Message ----- From: "Stefan Sch=C3=A4fer" =20 To: =20 Sent: Friday, July 16, 2010 11:32 PM=20 Subject: Re: LF: RE: DLF passive received with earth antenna=20 =20 > Ehm, 18000m^2? I have just calculated 5000m^2. It is A =3D 1m^2 * > 10EX= P((-94--20)/20), right?=20 >=20 > 73, Stefan=20 >=20 > =20 ----------MB_8CCF71EDB1C3A62_2268_5E57_webmail-d086.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="utf-8"
Dear Stefan, Jim, LF,
 
last weekend, I attempted a fieldstrength measurent of DHO38. = I used a small nonresonant loop (6 turns, 41 cm diameter, 0.792 m^2), dir= ectly connected to the soundcard, without a preamp or buffer. With the "Mi= c" slider fully up, full scale was 18.8 mV rms. The noise level (-98dB in= 17.6 Hz =3D 56.4 nV/sqrtHz) was low enough to measure the four strongest= MSK signals.
 
As Jim mentioned, the correction factor for thze MSK bandwidth depend= s on bandwidth, and I spend some time calibrating this. Direct integration= of the spectral density across the 200 bd MSK spectrum resulted in an eff= ective bandwidth of 105 Hz.  For Stefan's 2.93 Hz FFT (ie. 4.4 Hz noi= se bandwidth due to Hann window), the bandwidth factor should theoreticall= y be  20.2 - 6.4 =3D 14.8 dB.
 
For simplicity, I read the levels from SpecLab's waterfall cursor. Lo= ng averaging (> 10 s scroll with Optimum Waterfall averaging) is requir= ed to minimize the remaining raggedness of the spectrum. One should try to= avoid occasional times with apparent periodic patterns in the transmitted= data, leading to significant spectral peaks.
 
An additional offset resulted from the parabolic peak estimation, whi= ch is optimized for carriers, but tends to be 1.5 dB high for flat noise.= So in effect, Stefan would have to add  12.3 dB (rather than 14.8 or= 11 dB) to the cursor readout. For my measurements, I selected an 11.7 Hz= FFT and added 6.3 dB.
 
BTW There are probably better ways to read MSK levels from SpecLab,= either by using the new "pam().ampl" function, or simply selecting a larg= e enough resolution bandwidth (e.g. 187 Hz) to follow the signal modulatio= n.
 
My results for DHO38 at 475.3 km range were
 -79.5 dB =3D 4.11 uV (Saturday night 23:30)
 -82.1 dB =3D 3.05 uV (Sunday daytime 10:15)
 
With the effective height of the small loop
 heff =3D A / (lambda/2pi) =3D 0.388 mm at 23.4 kHz
(equivalent to Jim's formula), I get a fieldstrength of
 10.6 mV/m =3D 80.5 dBuV/m (night),
 7.86 mV/m =3D 77.9 dBuV/m (day).
 
Here is a table containing also the fieldstrength measurements of thr= ee other MSK stations:
kHz      dBuV/m      Cal= l     km
           night &n= bsp; day
45.9   68.3   56.1  (NSY)  1390,
23.4   80.5   77.9  (DHO)  475,
22.1   73.0 ~65.5 (GQD) 1155,
21.75 77.0   71.1 (HWU)  796.
 
On the German blog
http://www.mysnip.de/forum-archiv/thema/8773/109722/Sup= erpulse+auf+19_6+kHz.html
someone who worked at DHO38 states that they have eight 100 kW transmitter= s, feeding an array of eight antennas. With 80% combined antenna efficienc= y, they can radiate 640 kW (EMRP). This would theoretically result in
 E =3D 84.1 dBuV/m
here in Nuernberg. The difference to the measured values might be attibute= d to an ionospheric component, or ground loss, or simply to the fact that= they may not be regularly operating at full power.
 
To apply my DHO measurement to Stefan's ground loop experiment in Hei= delberg, we would have to scale daytime fieldstrength from 475 to to 411= km, giving
 E =3D 9.1 mV/m
at his site. The voltage at the antenna terminals was
 U =3D 44 mVpeak - 11dB + 12.3 dB =3D 36.1 mV rms.
Thus the effective height of the 280 m long earth antenna was
 heff =3D U/E =3D 3.97 m at 23.4 kHz,
giving a the ground loop area
 A =3D heff * lambda/2pi =3D 8090 m^2,
and an effective return current depth
 d =3D heff /length =3D 29 m.
 
This depth appears to be much less than half of the baseline length,= so it is probably indeed skin effect limited. Scaling the 23.4 kHz result= s to 9 kHz would give 1.6 times more skin depth, but 1.6 times less effect= ive height (ie. 2.5 m) due to the larger wavelength to loop length ratio.= Thus the transmit efficiency at 9 kHz would be about 26 dB less than that= of a 100 m kite antenna with similar loss resistance.
 
Kind regards,
Markus (DF6NM)
-----Urspr=C3=BCngliche Mitteilung-----
Von: James Moritz <james.moritz@btopenworld.com>
An: rsgb_lf_group@blacksheep.org
Verschickt: Sa., 17. Jul. 2010, 23:43
Thema: LF: RE: DLF passive received with earth antenna

Dear Stefan, LF Group, 
 
It gets confusing when the bandwidth changes! In this case, both measureme= nt bandwidths are much smaller than the modulation bandwidth, and the sign= al has a continuous spectrum, so it is reasonable to assume the measured= signal power will be proportional to the measurement bandwidth. The ampli= tude of the signal on the earth antenna was -20dB in 3Hz BW. To normalise= the measurements to a 3Hz FFT BW, you need to add 6dB to the amplitude of= the 1m^2 loop signal in 0.75Hz bandwidth, to give -94dB as you said. The= ratio of signal amplitudes is then 74dB, or a factor of about 5000. So th= e eqiuvalent area of the earth antenna is 5000m^2. 
 
Adding Markus' factor of 11dB to give the total signal amplitude from the= 1m^2 loop gives -83dB, 74 dB below your reference level of 44mV =3D -9dB.= Therefore the 1m^2 loop EMF is about 9uV, corresponding to FS of DHO38 be= ing about 18mV/m. If this is correct, it corresponds to about 1.1MW ERP,= which is impressive, but since the signal is down in the noise in your sy= stem, these figures can only be a very rough estimate. 
 
Cheers, Jim Moritz 
73 de M0BMU 
 
----- Original Message ----- From: "Stefan Sch=C3=A4fer" <schaefer@i= up.uni-heidelberg.de> 
To: <rsgb_lf_group@blacksheep.org> 
Sent: Friday, July 16, 2010 11:32 PM 
Subject: Re: LF: RE: DLF passive received with earth antenna 
 
> Ehm, 18000m^2? I have just calculated 5000m^2. It is A =3D 1m^2 * >= ; 10EXP((-94--20)/20), right? 
> 
> 73, Stefan 
> 
>  
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