Return-Path: Received: from mtain-mb03.r1000.mx.aol.com (mtain-mb03.r1000.mx.aol.com [172.29.96.23]) by air-md03.mail.aol.com (v129.4) with ESMTP id MAILINMD032-8b7d4c1be6123e1; Fri, 18 Jun 2010 17:33:06 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mb03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 8E44038000094; Fri, 18 Jun 2010 17:33:04 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1OPjAg-0007Dv-K3 for rs_out_1@blacksheep.org; Fri, 18 Jun 2010 22:32:18 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1OPjAg-0007Dm-2B for rsgb_lf_group@blacksheep.org; Fri, 18 Jun 2010 22:32:18 +0100 Received: from mail-bw0-f43.google.com ([209.85.214.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1OPjAe-0002WZ-2b for rsgb_lf_group@blacksheep.org; Fri, 18 Jun 2010 22:32:18 +0100 Received: by bwz19 with SMTP id 19so527940bwz.16 for ; Fri, 18 Jun 2010 14:32:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=JWRBCJxu7zOjA3gXKPeySeFzMlBj24NXzlCn5b/Tp7Q=; b=jFXvvOpjUQhUw7iUZw9ISp34D7e1K6HEq1LBFQIkYaSVKknbmjsfDp75+GXXgDlO99 d57GVD0RarAngZI5xiWLP/1wdDqAHDCCnNoa8DLrEzjN5/Vhth+zNPFRd3WcKM8SBbez 6tcvRuMQ+TcDLuHXYen1M9L1WxxihUBuie27c= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=VR4eVe7fuFJ/affsO20y8/cfhEIFIooWzcYgyQRwJyDF/3Y4Qcxo+qqRe2uRG3U03X Oqj9qq4xJsTxAAEP1cGI6XxzWUh8ETe7Ay3yDq4uj5rF/4mVEOOSol+Ef9LDU5MAXE1q tQbrmYfj7LSXC48TiBTLTs/txw5IqDrLV/rsw= MIME-Version: 1.0 Received: by 10.204.81.89 with SMTP id w25mr1298524bkk.39.1276896735093; Fri, 18 Jun 2010 14:32:15 -0700 (PDT) Received: by 10.204.100.69 with HTTP; Fri, 18 Jun 2010 14:32:15 -0700 (PDT) In-Reply-To: References: Date: Fri, 18 Jun 2010 22:32:15 +0100 Message-ID: From: Roger Lapthorn 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: LF: RE: Earth electrode loop area - I'm struggling Content-Type: multipart/alternative; boundary=0016e6d64c834f6548048954b002 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_20_30,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-m257.1 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d60174c1be610329b X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --0016e6d64c834f6548048954b002 Content-Type: text/plain; charset=ISO-8859-1 Many thanks for this calculation Rik - you are a real star! I was using L^2 which may have been my problem (I found this in the RSGB LF handbook, which I guess is wrong). This makes the area some 600 times bigger than my calculation and a believable figure now. Now looking at the actual area of the loop that is "in the air" (as opposed to in the ground) I estimate this as being: 15m^2 (the run along the garden fence) 5m^2 (the part under the sloping roof of the study) 30m^2 (the area under the house between the copper pipes and ground) i.e. about 50m^2 This suggests the current flow is not deep within the soil as only an additional 20m^2 is in the ground. This would also suggest that the impact of higher conductivity soil should not be that great, as in the limit all the current flows along the surface? Still, this was a worthwhile exercise and I have learnt something from it, and that is what our wonderful hobby is all about. Thanks again Rik. 73s Roger G3XBM On 18 June 2010 22:10, Rik Strobbe wrote: > Hello Roger, > > my pennyworth: > > assuming > - 50uW ERP > - antenna is traded as a loop (gain = -0.4dBd) > > Due to the negative gain (-0.4dB versus dipole) a loop antenna must > "radiate" 55uW to get 50uW ERP. > Since the antenna feeding current is 0.15A the radiation resistance is 2.44 > milliOhm (R= P/I^2) > The radiation resistance of a small loop is : Ra = 320xPi^4*A^2/L^4 > where A = loop area (m^2) and L = wavelength (m) > For 500kHz Ra = 5*10^(-7)*A^2 or A = 1416*sqrt(Ra) > If Ra = 0.00244 Ohm then effective the loop area is 70m^2 > > 73, Rik ON7YD - OR7T > > > ------------------------------ > *Van:* owner-rsgb_lf_group@blacksheep.org [ > owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [ > rogerlapthorn@gmail.com] > *Verzonden:* vrijdag 18 juni 2010 22:29 > *Aan:* rsgb_lf_group@blacksheep.org > *Onderwerp:* LF: Earth electrode loop area - I'm struggling > > Please can someone help me with the maths? I've been trying to work out > my effective loop area and I cannot get sensible answers. These are the > measured or estimated numbers I have: > > Voltage across "loop" = 24.48V rms - measured > Current flowing in "loop" = 0.15A - measured > ERP (from far field levels) = 50-100uW (may be less) based on -18dB S/N > with M0BMU > > From these figures I should be able to work out the loop area, but either > my calculations are wrong or the figure is correct and the effective loop > area is very very small. > > Help! > > 73s > Roger G3XBM > > -- > http://g3xbm-qrp.blogspot.com/ > http://www.g3xbm.co.uk > http://www.youtube.com/user/g3xbm > G3XBM GQRP 1678 ISWL G11088 > -- http://g3xbm-qrp.blogspot.com/ http://www.g3xbm.co.uk http://www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 --0016e6d64c834f6548048954b002 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Many thanks for this calculation Rik - you are a real star!

I was= using L^2 which may have been my problem (I found this in the RSGB LF han= dbook, which I guess is wrong). This makes the area some 600 times bigger= than my calculation and a believable figure now.

Now looking at the actual area of the loop that is "in the air&qu= ot; (as opposed to in the ground) I estimate this as being:

15m^2= =A0=A0=A0=A0=A0=A0=A0=A0=A0 (the run along the garden fence)
5m^2=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 (the part under the sloping roof of the stu= dy)
30m^2=A0=A0=A0=A0=A0=A0=A0=A0=A0 (the area under the house between the cop= per pipes and ground)

i.e. about 50m^2

This suggests the cur= rent flow is not deep within the soil as only an additional 20m^2 is in th= e ground. This would also suggest that the impact of higher conductivity= soil should not be that great, as in the limit all the current flows alon= g the surface?

Still, this was a worthwhile exercise and I have learnt something from= it, and that is what our wonderful hobby is all about.

Thanks agai= n Rik.

73s
Roger G3XBM




On 18 June 2010 22:10, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>= wrote:
Hello Roger,
=A0
my pennyworth:
=A0
assuming
- 50uW= ERP
- antenna is traded as a loop (gain= =3D -0.4dBd)
=A0
Due to the negative gain (-0.4dB ver= sus dipole) a loop antenna must "radiate" 55uW to get 50uW ERP.<= /font>
Since the antenna feeding current is= 0.15A the radiation resistance is 2.44 milliOhm (R=3D P/I^2)
The radiation resistance of a small= loop is : Ra =3D 320xPi^4*A^2/L^4
where A =3D loop area (m^2) and=A0L= =3D wavelength (m)
For 500kHz Ra =3D 5*10^(-7)*A^2 or= A =3D 1416*sqrt(Ra)
If=A0Ra =3D 0.00244 Ohm then effecti= ve the loop area is 70m^2
=A0
73, Rik=A0 ON7YD - OR7T
=A0
=A0
Van: owner-rsgb_lf= _group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Ro= ger Lapthorn [rogerlapthorn@gmail.com]
Verzonden: vrijdag 18 juni 2010 22:29
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: Earth electrode loop area - I'm struggling

Please can someone help me with the maths? I've been trying to wo= rk out my effective loop area and I cannot get sensible answers. These are= the measured or estimated numbers I have:

Voltage across "loop"=A0 =3D 24.48V rms=A0 - measured
Current flowing in "loop" =3D 0.15A - measured
ERP (from far field levels) =3D 50-100uW (may be less) based on -18dB S/N= with M0BMU

>From these figures I should be able to work out the loop area, but either= my calculations are wrong or the figure is correct and the effective loop= area is very very small.

Help!

73s
Roger G3XBM

--
http://g3xbm-= qrp.blogspot.com/
http://www.g3xbm.co.u= k
http://www= .youtube.com/user/g3xbm
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088



--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088
--0016e6d64c834f6548048954b002--