Return-Path: Received: from rly-dd02.mx.aol.com (rly-dd02.mail.aol.com [172.19.141.149]) by air-dd04.mail.aol.com (v121_r4.4) with ESMTP id MAILINDD044-b64493a51f19b; Sat, 06 Dec 2008 05:20:55 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-dd02.mx.aol.com (v121_r4.4) with ESMTP id MAILRELAYINDD026-b64493a51f19b; Sat, 06 Dec 2008 05:20:35 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1L8uGk-0004fc-JI for rs_out_1@blacksheep.org; Sat, 06 Dec 2008 10:20:14 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1L8uGk-0004fT-2C for rsgb_lf_group@blacksheep.org; Sat, 06 Dec 2008 10:20:14 +0000 Received: from mail.claranet.pt ([195.22.17.19]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1L8uGh-0004hE-Uv for rsgb_lf_group@blacksheep.org; Sat, 06 Dec 2008 10:20:14 +0000 Received: from mail.claranet.pt (ste [10.1.2.2]) by mail.claranet.pt (Postfix) with ESMTP id 1C74954313 for ; Sat, 6 Dec 2008 10:20:07 +0000 (WET) Received: from slave_13.esoterica.pt (unknown [80.172.156.70]) (Authenticated sender: ew9gtj) by mail.claranet.pt (Postfix) with ESMTP id 3007154310 for ; Sat, 6 Dec 2008 10:20:06 +0000 (WET) Message-Id: <5.2.0.9.2.20081206100245.024b04f8@pop.claranet.pt> X-Sender: ew9gtj@pop.claranet.pt X-Mailer: QUALCOMM Windows Eudora Version 5.2.0.9 Date: Sat, 06 Dec 2008 10:19:49 +0000 To: rsgb_lf_group@blacksheep.org From: Brian Rogerson In-Reply-To: <20081120093621.2BE8031E702@smtps01.kuleuven.be> References: <49251A7B.6050603@telia.com> <001e01c94a77$cc1fa780$a402a8c0@Inspiron> <004e01c94a9c$dddbe860$0900a8c0@AM> <1227166876.4925149c95ec8@imp.netikka.net> <49251A7B.6050603@telia.com> Mime-Version: 1.0 X-Karma: 0: X-Spam-Score: 0.7 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,MIME_HTML_MOSTLY=0.699 Subject: Re: LF: ERP calculations / measurements Content-Type: multipart/mixed; boundary="=====================_440148720==_" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.4 required=5.0 tests=HTML_EVENT_UNSAFE,HTML_MESSAGE, HTML_RELAYING_FRAME 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 --=====================_440148720==_ Content-Type: multipart/alternative; boundary="=====================_440148720==.ALT" --=====================_440148720==.ALT Content-Type: text/plain; charset="us-ascii"; format=flowed Rik and LF Your email below prompted me to carry out another afternoon of measurements from higher ground for the station FS/ERP survey. The results seem spectacular though I am unsure of what they mean. I hope to place the data on my web site later. 73, Brian CT1DRP At 09:36 20/11/2008, you wrote: >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 > --=====================_440148720==.ALT Content-Type: text/html; charset="us-ascii" Rik and LF

Your email below prompted me to carry out another afternoon of measurements from higher ground for the station FS/ERP survey.  The results seem spectacular though I am unsure of what they mean.  I hope to place the data on my web site later.

73, Brian CT1DRP



At 09:36 20/11/2008, you wrote:
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

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