Return-Path: Received: from mtain-dd04.r1000.mx.aol.com (mtain-dd04.r1000.mx.aol.com [172.29.64.144]) by air-de01.mail.aol.com (v127_r1.1) with ESMTP id MAILINDE014-5ea54b866e9d327; Thu, 25 Feb 2010 07:35:41 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-dd04.r1000.mx.aol.com (Internet Inbound) with ESMTP id D36E6380000D2; Thu, 25 Feb 2010 07:35:39 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NkcvB-0003Vb-P8 for rs_out_1@blacksheep.org; Thu, 25 Feb 2010 12:34:25 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NkcvB-0003VR-8M for rsgb_lf_group@blacksheep.org; Thu, 25 Feb 2010 12:34:25 +0000 Received: from mail-bw0-f215.google.com ([209.85.218.215]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Nkcv9-0004SP-1D for rsgb_lf_group@blacksheep.org; Thu, 25 Feb 2010 12:34:25 +0000 Received: by bwz7 with SMTP id 7so4484487bwz.4 for ; Thu, 25 Feb 2010 04:34:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=HZHDRrb4ETsdshtMEnRxWp6ZJvbPe8B027YkUzgQagg=; b=itHk9dG2UWFmDSY6zLGYJi/GML52C5jPPVsHUpKH5SF/ALWMBHF55xw+pQCWjPH57m 6OHl7Ve8FUsgvrNj8Rbpv2uTqfOKckaulUiRvuGwc7/nwrEiDMVbUibDeUchhrPT53wG X2F5Ix5ntWG6YfdOd2BgRIkbFG80tnoDg8G4o= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=TCRUOVkRXJyT1Bq9akt97PbLxig8bS0sgBP5QhfYV97QFeCAFn3ADdw43ojAdNsIQX aLJIbvLiFycW2KsYhhQL5Lqj7DBW2zQTYMI8X9lm7zGCsMbquPjtlaUGgjLXk7faY9+1 NWiOjlBqg8rsfIHPgJ/3715Xu70ew3dNj9XX8= MIME-Version: 1.0 Received: by 10.204.10.3 with SMTP id n3mr677028bkn.81.1267101257222; Thu, 25 Feb 2010 04:34:17 -0800 (PST) In-Reply-To: References: <818138.8525.qm@web28102.mail.ukl.yahoo.com> <38A51B74B884D74083D7950AD0DD85E82A1B1A@File-Server-HST.hst.e-technik.tu-darmstadt.de> Date: Thu, 25 Feb 2010 12:34:17 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: AW: LF: RE: Re: VLF_8.79 kHz Content-Type: multipart/alternative; boundary=0003255574d254ca0804806c0060 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_UNSAFE, 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-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m246.1 ; domain : googlemail.com DKIM : pass x-aol-sid: 3039ac1d40904b866e9b3ed5 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --0003255574d254ca0804806c0060 Content-Type: text/plain; charset=ISO-8859-1 Yes, but what is the gain / antenna factor of your Miniwhip? Measuing -115dBm means little in itself, you need to convert this to a calibrated V/m form. IF the miniwhip were *exactly 1m long* and positioned over a good groundplane, fed an *infinite input impedance*, zero input capacitance voltage follower amp with *unity voltage gain into 50 ohms*, then -115dBm would equate to 0.4uV/m in 24Hz, or .08uV/m/ SQRT Hz. If the value quoted recently of 150dB kTB is assumed, which is 25dB lower that my original calculation, it suggests a value in the region of 4uV / m / SQRT Hz may be more typical. Andy www.g4jnt.com On 25 February 2010 12:02, Roelof Bakker wrote: > Hello Andy, > > I measured the noise on 8800 Hz received on my mini-whip. > Receiver: SPM-30, BW = 24 Hz, noise level = -115 dBm > > The same measurement with a PERSEUS SDR and a bandwidth of 20 Hz revealed a > noise level of -122 dBm. > PERSEUS has an input isolating transformer, which rolls off below 15 kHz, > hence the lower measured noise level. > > It does not look too bad to me, really. > > 73, > Roelof Bakker, pa0rdt > > --0003255574d254ca0804806c0060 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Yes, but what is the gain / antenna factor of your Miniwhip?=A0
Measuing -115dBm=A0means little=A0in itself, you need to convert this= to a calibrated V/m form.
=A0
IF the miniwhip were exactly 1m long and positioned over a goo= d groundplane,=A0fed an infinite input impedance, zero input capaci= tance voltage follower amp with unity voltage gain into 50 ohms, th= en -115dBm would equate to 0.4uV/m in 24Hz,=A0 or=A0 .08uV/m/ SQRT=A0Hz.= =A0=A0=A0
=A0
If the value quoted recently of 150dB kTB=A0 is assumed, which is 25d= B=A0lower that=A0my original calculation, it=A0suggests a value =A0in the= region of=A0 4uV / m / SQRT Hz may be more typical.
On 25 February 2010 12:02, Roelof Bakker <= roelof@ndb.demon.nl> wrote:
Hello Andy,

I measured= the noise on 8800 Hz received on my mini-whip.
Receiver: SPM-30, BW = =3D 24 Hz, noise level =3D -115 dBm

The same measurement with a PERSEUS SDR and a bandwidth of 20 Hz revea= led a noise level of -122 dBm.
PERSEUS has an input isolating transform= er, which rolls off below 15 kHz, hence the lower measured noise level.
It does not look too bad to me, really.

73,
Roelof Bakker, pa0rdt


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