Return-Path: Received: (qmail 25658 invoked from network); 7 Jun 2000 09:40:55 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by grants.core.plus.net.uk with SMTP; 7 Jun 2000 09:40:55 -0000 Content-Transfer-Encoding: 8bit Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12zctO-0006Vk-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 07 Jun 2000 11:16:58 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: from fm215.facility.pipex.com ([194.131.104.225]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12zctN-0006Vf-00 for rsgb_lf_group@blacksheep.org; Wed, 07 Jun 2000 11:16:58 +0100 Received: from isis (userec82.uk.uudial.com [62.188.10.162]) by fm215.facility.pipex.com (8.9.3/8.9.3) with ESMTP id KAA23379 for ; Wed, 7 Jun 2000 10:28:42 +0100 (BST) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <4.2.0.58.20000607100135.00966c00@mail.pncl.co.uk> X-Sender: blanch@mail.pncl.co.uk X-Mailer: QUALCOMM Windows Eudora Pro Version 4.2.0.58 Date: Wed, 07 Jun 2000 10:25:14 +0100 To: rsgb_lf_group@blacksheep.org From: "Walter Blanchard" Subject: LF: Formula MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: I found the following in an article recently. Quote: "The intensity E (known as the field strength) of a transmission at a distance D from a source transmitting P watts of RF power via a half-wave dipole in a free, unobstructed space, can be estimated using the formula: E=(7*sqrt (P))/D. Thus, for a 2 watt transmitter, the theoretical field strength in free space at one metre distance is approximately 10 V/m and at 100 metres distance 0.1 V/m" This formula is new to me and I can't find it in any textbooks I have. Since it ignores frequency shouldn't it be power flux per unit area and not field strength? Can anyone tell me where it comes from? Walter G3JKV.