Return-Path: Received: from rly-mh07.mx.aol.com (rly-mh07.mail.aol.com [172.21.166.143]) by air-mh04.mail.aol.com (v121_r4.4) with ESMTP id MAILINMH044-be849252fb73da; Thu, 20 Nov 2008 04:37:18 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mh07.mx.aol.com (v121_r4.4) with ESMTP id MAILRELAYINMH078-be849252fb73da; Thu, 20 Nov 2008 04:36:57 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1L35xf-0008WH-AD for rs_out_1@blacksheep.org; Thu, 20 Nov 2008 09:36:31 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1L35xe-0008W8-Ry for rsgb_lf_group@blacksheep.org; Thu, 20 Nov 2008 09:36:30 +0000 Received: from cavuit01.kulnet.kuleuven.be ([134.58.240.43]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1L35xd-0002WB-UH for rsgb_lf_group@blacksheep.org; Thu, 20 Nov 2008 09:36:30 +0000 Received: from smtps01.kuleuven.be (smtpshost01.kulnet.kuleuven.be [134.58.240.74]) by cavuit01.kulnet.kuleuven.be (Postfix) with ESMTP id 8FFDE7B8054 for ; Thu, 20 Nov 2008 10:36:21 +0100 (CET) Received: from smtps01.kuleuven.be (localhost [127.0.0.1]) by smtps01.kuleuven.be (Postfix) with ESMTP id 377E231E703 for ; Thu, 20 Nov 2008 10:36:21 +0100 (CET) Received: from dell-rik.fys.kuleuven.be (dhcp-10-33-85-199.fys.kuleuven.be [10.33.85.199]) by smtps01.kuleuven.be (Postfix) with ESMTP id 2BE8031E702 for ; Thu, 20 Nov 2008 10:36:21 +0100 (CET) X-Mailer: QUALCOMM Windows Eudora Version 7.1.0.9 Date: Thu, 20 Nov 2008 10:36:49 +0100 To: rsgb_lf_group@blacksheep.org X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe In-Reply-To: <49251A7B.6050603@telia.com> References: <001e01c94a77$cc1fa780$a402a8c0@Inspiron> <004e01c94a9c$dddbe860$0900a8c0@AM> <1227166876.4925149c95ec8@imp.netikka.net> <49251A7B.6050603@telia.com> Mime-Version: 1.0 Message-Id: <20081120093621.2BE8031E702@smtps01.kuleuven.be> X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: LF: ERP calculations / measurements Content-Type: text/plain; charset="us-ascii"; format=flowed 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=none 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-IP: 193.82.116.20 Hello group, it seems to be generally accepted that a small vertical antenna has a gain of 3 (4.77dBi / 2.62dBd), due to the radiation pattern in the vertical plane. But in very few cases this gain seems to be measured when doing ERP measurements. As far as I understand this gain of 3 is based on a perfect ground (endless conductivity) that acts as a (perfect) mirror and thus creates the "mirror image" needed for radiation. But what about a short vertical antenna above a not-so-perfect ground? I have done some simulations with MMANA-GAL (15m high vertical at 500kHz) and over a perfect ground I get the expected 4.77dBi and a take-off angle of 0 degrees. If the conductivity is not endless the gain drops and the take-off angle rises: 1000mS/m (salt water) = 4.5dBi / 9 degrees 500mS/m (clay) = 4.4dBi / 10 degrees 50mS/m (marsh) = 3.9dBi / 14 degrees 15mS/m (loam) = 3.5dBi / 17 degrees 5mS/m (wet sand) = 2.9dBi / 21 degrees 0.05mS/m (dry sand) = -1.5dBi / 32 degrees Could this explain (a part of) the missing dB's ? 73, Rik ON7YD - OR7T Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm