Return-Path: Received: from mtain-mh08.r1000.mx.aol.com (mtain-mh08.r1000.mx.aol.com [172.29.96.220]) by air-db05.mail.aol.com (v129.4) with ESMTP id MAILINDB054-86994bfce2ca2f8; Wed, 26 May 2010 04:58:50 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mh08.r1000.mx.aol.com (Internet Inbound) with ESMTP id 0A32A380000A8; Wed, 26 May 2010 04:58:48 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OHCQh-0002cm-G2 for rs_out_1@blacksheep.org; Wed, 26 May 2010 09:57:35 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OHCQh-0002cd-3z for rsgb_lf_group@blacksheep.org; Wed, 26 May 2010 09:57:35 +0100 Received: from mhost02c.leeds.ac.uk ([129.11.76.154]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OHCQf-0003AN-Bb for rsgb_lf_group@blacksheep.org; Wed, 26 May 2010 09:57:35 +0100 Received: from APOLLO2.ds.leeds.ac.uk (apollo2.leeds.ac.uk [129.11.5.5]) by mhost02c.leeds.ac.uk (8.14.3/8.14.3) with ESMTP id o4Q8vRlo029847 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NOT) for ; Wed, 26 May 2010 09:57:27 +0100 (BST) Received: from HERMES8.ds.leeds.ac.uk ([fe80::39ce:23e:d0b5:7e24]) by APOLLO2.ds.leeds.ac.uk ([129.11.5.5]) with mapi; Wed, 26 May 2010 09:57:27 +0100 From: Chris Trayner To: "rsgb_lf_group@blacksheep.org" Date: Wed, 26 May 2010 09:57:25 +0100 Thread-Topic: LF: AW: 8.97kHz - Near field and radiated signals? Thread-Index: Acr8sXZ9UofLCdlTReG4p3CN0Y5qcQ== Message-ID: <475317E6-80B4-4A03-B046-E64827223B70@leeds.ac.uk> References: <38A51B74B884D74083D7950AD0DD85E82A1C00@File-Server-HST.hst.e-technik.tu-darmstadt.de> , In-Reply-To: Accept-Language: en-US, en-GB Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US, en-GB MIME-Version: 1.0 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: AW: 8.97kHz - Near field and radiated signals? Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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: 3039ac1d60dc4bfce2c85023 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) Hi Rik, > the near fiels signal drops with the 3rd power of the distance. I think you'll find it's the H field that goes as the inverse 3rd power.= The voltage in the Rx ant is proportional to this, and the power is propo= rtional to the square of that. Thus the power, which is what dBs describe,= goes as the inverse 6th power. > So 3km versus 0.4km =3D 422 times weaker =3D -26dB In other words you need to convert your 422 not as 10 log(422) but as 20= log(422), which gives -52dB. Sorry to be the bringer of bad news ;-( Roger also said > I am confused by the near field attenuation rates quoted. Some quote 18d= B for doubling distance=20 This fits: double the distance is 1/8 H field, 1/64 power, 18dB. 73, Chris G4OKW ----------------------- Dr Chris Trayner School of Electronic & Electrical Engineering, The University of Leeds, Leeds LS2 9JT, United Kingdom Tel: +44 113 34 32053 Fax: +44 113 34 32032