Return-Path: Received: from mtain-df10.r1000.mx.aol.com (mtain-df10.r1000.mx.aol.com [172.29.64.222]) by air-md08.mail.aol.com (v127_r1.1) with ESMTP id MAILINMD083-8b924b8998f237c; Sat, 27 Feb 2010 17:13:06 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-df10.r1000.mx.aol.com (Internet Inbound) with ESMTP id 23E953800008F; Sat, 27 Feb 2010 17:13:05 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NlUtC-0003sP-IU for rs_out_1@blacksheep.org; Sat, 27 Feb 2010 22:11:58 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NlUtC-0003sG-1x for rsgb_lf_group@blacksheep.org; Sat, 27 Feb 2010 22:11:58 +0000 Received: from imr-db03.mx.aol.com ([205.188.91.97]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NlUtA-00075W-2U for rsgb_lf_group@blacksheep.org; Sat, 27 Feb 2010 22:11:58 +0000 Received: from mtaout-da05.r1000.mx.aol.com (mtaout-da05.r1000.mx.aol.com [172.29.51.133]) by imr-db03.mx.aol.com (8.14.1/8.14.1) with ESMTP id o1RMBjP8006687 for ; Sat, 27 Feb 2010 17:11:45 -0500 Received: from Black (e179166161.adsl.alicedsl.de [85.179.166.161]) by mtaout-da05.r1000.mx.aol.com (WebSuites/MUA Thirdparty client Interface) with ESMTPA id 44B43E000094 for ; Sat, 27 Feb 2010 17:11:44 -0500 (EST) Message-ID: <9C37FBB31AF6404980D3039622DBE323@Black> From: "Markus Vester" To: References: <931424D0B09442018D818E6AD1E5A63A@White> <9afca2641002260907k56b21a49p386d43b0be234436@mail.gmail.com> In-Reply-To: Date: Sat, 27 Feb 2010 23:11:31 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6000.16480 X-MIMEOLE: Produced By Microsoft MimeOLE V6.0.6000.16669 x-aol-global-disposition: G x-aol-sid: 3039ac1d33854b8998a00f34 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: 9kHz noise level Content-Type: multipart/alternative; boundary="----=_NextPart_000_0013_01CAB802.328E1C60" 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: 3039ac1d40de4b8998f11dde X-AOL-IP: 193.82.116.20 ------=_NextPart_000_0013_01CAB802.328E1C60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear Jim, LF, yes I'm aware of the fact that the shielding from trees etc is more si= gnificant at lower frequency. Their ohmic conductance becomes a better= shunt in comparison with decreasing capacitive admittance, somewhat= similar to a C-R highpass equivalent circuit. There used to be two be= autiful 15 m high fir trees in the vicinity of our house. At 137 kHz,= I measured a ~ 15% increase in effective height when the trees were= deeply frozen, but the effect on 9 kHz may have been more severe. A= couple of years ago our neighbours had these trees chopped down, good= for LF but otherwise sad. In April 2003, I attempted to transmitt an 8.97 kHz carrier, radiating= about 1 microwatt from my normal LF antenna (220 pF at ~ 9m eff. heig= ht). I drove around and stopped in different places, putting up a 6m= fishing pole with a wire, connected to a resonant circuit and the lap= top soundcard. Each time I took a short Spectrogram full-band screensh= ot, along with a narrowband capture from a special Argo version, patch= ed for 22 kHz samplerate. An assembly of the screenshots is at http:/= /freenet-homepage.de/df6nm/8970_ALL.gif. Maximum detection range was= 6 km, just marginally outside the reactive nearfield. No noiseblankin= g was attempted at the time. If you look at the Spectrogram strips, you can see that the first (1.6= km) and third (6.0 km) images have a much lower absolute receive leve= l. At first I thought something was wrong with the receive antenna, un= til I realized that this was purely due to these sites being in a fore= sted area. I have now rigged up SpecLab again for VLF reception. The Russian Alph= a beacons seem to be usefiul calibration markers, the nearest one is= currently about 20 dB SNR here in a 42 Hz FFT. Does anybody in the gr= oup have information about their EMRP, or has someone attempted to mea= sure their fieldstrength in Europe? Best 73, Markus (DF6NM) ----- Original Message -----=20 From: James Moritz=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Friday, February 26, 2010 6:51 PM Subject: Re: LF: Re: 9kHz noise level Dear Markus, LF Group, I checked the noise level again during the daytime, and the noise le= vel was about 6dB lower than last night, i.e. about 13uV/m per sqrtHz One possibility for the discrepancy between results is that the effe= ctive height of your antenna is reduced at VLF compared to the LF cali= bration point. In my transmitting vertical field strength measuring se= ssions on 500k, 136k and earlier 73k, the Heff of the same antenna wor= ks out consistently less as the frequency is reduced. I think this is= due to increased "site loss" due to surrounding trees at the lower fr= equencies.=20 H-field sensing loop antennas can be expected to be less affected.= Of course, if there are no trees near your antenna, that theory is bl= own out of the water... Cheers, Jim Moritz 73 de M0BMU ------=_NextPart_000_0013_01CAB802.328E1C60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Dear Jim, LF,
 
yes I'm aware of the fact that the sh= ielding from=20 trees etc is more significant at lower frequency. Their = ;ohmic=20 conductance becomes a better shunt in comparison with=20 decreasing capacitive admittance, somewhat similar to a C-R highp= ass=20 equivalent circuit. There used to be two beautiful 15 m high= fir trees=20 in the vicinity of our house. At 137 kHz, I measured a ~=20 15% increase in effective height when the trees were deeply= frozen,=20 but the effect on 9 kHz may have been more severe. A couple of years= ago our=20 neighbours had these trees chopped down, good for LF but otherwise=20 sad.
 
In April 2003, I attempted to tr= ansmitt an=20 8.97 kHz carrier, radiating about 1 microwatt from my normal LF= =20 antenna (220 pF at ~ 9m eff. height). I drove around and sto= pped in=20 different places, putting up a 6m fishing pole with a wire,= connected=20 to a resonant circuit and the laptop soundcard. Each time I took= a short=20 Spectrogram full-band screenshot, along with a narrowband capture= from a=20 special Argo version, patched for 22 kHz samplerate. An assembly= of the=20 screenshots is at  http://freenet-homepage.de/df6nm/8970_ALL.gif<= /A>.=20 Maximum detection range was 6 km, just marginally outside the reactive= =20 nearfield. No noiseblanking was attempted at the time.
 
If you look at the Spectrogram strips= , you can see=20 that the first (1.6 km) and third (6.0 km) images have a muc= h lower=20 absolute receive level. At first I thought something was wrong wi= th the=20 receive antenna, until I realized that this was purely due to the= se sites=20 being in a forested area.
 
I have now rigged up SpecLab aga= in=20 for VLF reception. The Russian Alpha beacons seem to=20 be usefiul calibration markers, the nearest one is currently abou= t 20 dB=20 SNR here in a 42 Hz FFT. Does anybody in the group have informati= on about=20 their EMRP, or has someone attempted to measure their fieldstreng= th in=20 Europe?
 
Best 73,
Markus (DF6NM)
----- Original Message -----
Sent: Friday, February 26, 20= 10 6:51=20 PM
Subject: Re: LF: Re: 9kHz noi= se=20 level

Dear Markus, LF Group,

I checked the noise level again= during the=20 daytime, and the noise level was about 6dB lower than last night, i.= e. about=20 13uV/m per sqrtHz

One possibility for the discrepancy between= results=20 is that the effective height of your antenna is reduced at VLF compa= red to the=20 LF calibration point. In my transmitting vertical field strength mea= suring=20 sessions on 500k, 136k and earlier 73k, the Heff of the same antenna= works out=20 consistently less as the frequency is reduced. I think this is due= to=20 increased "site loss" due to surrounding trees at the lower frequenc= ies.=20
 
H-field sensing loop antennas can be expected to be less affect= ed. Of=20 course, if there are no trees near your antenna, that theory is blow= n out of=20 the water...

Cheers, Jim Moritz
73 de=20 M0BMU


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