Return-Path: Received: from mtain-db07.r1000.mx.aol.com (mtain-db07.r1000.mx.aol.com [172.29.64.91]) by air-di07.mail.aol.com (v128.1) with ESMTP id MAILINDI074-eb654bb4fb56283; Thu, 01 Apr 2010 16:00:22 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-db07.r1000.mx.aol.com (Internet Inbound) with ESMTP id E68BB38000091; Thu, 1 Apr 2010 16:00:19 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NxQXD-0000j2-BK for rs_out_1@blacksheep.org; Thu, 01 Apr 2010 20:58:35 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NxQXC-0000it-OY for rsgb_lf_group@blacksheep.org; Thu, 01 Apr 2010 20:58:34 +0100 Received: from mail-bw0-f215.google.com ([209.85.218.215]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NxQXA-0000ZY-88 for rsgb_lf_group@blacksheep.org; Thu, 01 Apr 2010 20:58:34 +0100 Received: by bwz7 with SMTP id 7so1206688bwz.4 for ; Thu, 01 Apr 2010 12:58:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:received:message-id:subject:from:to:content-type; bh=nBVV6ZplQ5nsj3JoQM0pTVOthQSJwGGydWjQhsbhumU=; b=XbXK54EjrZr8K8f2AyMwn8c5AfHrR+tL7Shlyn5D3SHGg2DMRS5JjtvfiOaUYFbVg2 SV0zTrrpkJbUVbqzTUKm9JpQKsaG1VOhh92F1MLWHaVEZUpNdwcH4Xzrkd1I8WFYK5OA 2vTG9J/yc7gvoDcIOU7gOCRcgRwcvOGLoCYXQ= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=RoPAux+RLOSXGv6gINRXP1BDcTquZNHvXVo+LW+c+SmMhBQXtuwlVxv9Dh7zq1AtXV zTZoGox4rYkTuea6g09bQvztEdw+5Dvewo6CygX1o37ddh0G1hJAnXcsf2SJByrSNov9 T6kmnrfNHkzi2m0msUG0DYaim+sy2Y43HAfnk= MIME-Version: 1.0 Received: by 10.204.55.204 with HTTP; Thu, 1 Apr 2010 12:58:25 -0700 (PDT) In-Reply-To: <841031C22EC944FEB2BB3E1DC237717E@acer3f31164f8b> References: <001d01cad190$aa92e590$0901a8c0@lark> <841031C22EC944FEB2BB3E1DC237717E@acer3f31164f8b> Date: Thu, 1 Apr 2010 20:58:25 +0100 Received: by 10.204.36.208 with SMTP id u16mr1847739bkd.168.1270151905666; Thu, 01 Apr 2010 12:58:25 -0700 (PDT) Message-ID: From: Andy Talbot 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: Re: E-Field Probe calibration question Content-Type: multipart/alternative; boundary=00032555a08225e74504833249af 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-m274.1 ; domain : googlemail.com DKIM : pass x-aol-sid: 3039ac1d405b4bb4fb534ec2 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --00032555a08225e74504833249af Content-Type: text/plain; charset=ISO-8859-1 On the basis of two measurements out in the field - the results suggests the voltage being picked up is slightly more than the effective length as stated, but resukts for such a quick first approxiomation are in teh right region: At two /P monitoring sites at distances of 3.5 and 14km, the measured power was calculated back to a field strength using the quoted antenna factor, then this E field was related to ERP using the standard equation. At 3.5km the ERP worked out at around 200mW which isn't too far from what I thought it was from Rloss / Rrad calculations. BUT, the Rx was surrounded by trees and a power cable close by, so could reasonably be expected to be lower than it should be. The second site was in the middle of flat land, at the top of a Hill (Lane End Down for those microwavers on this reflector), where there were virtually no local screening. ERP calculated back to 900mW. This result is too high, suggesting the E-Field probe antenna is picking up more signal than it ought to. I need to make some more measurements further afield, and to compare with a loop before coming to any conclusion - but an afternoon pleasently spent getting a measurement in the right region at least. Andy www.g4jnt.com On 1 April 2010 13:05, Mike McAlevey wrote: > Hi Andy. > I would go along with Alan's thinking. It's about the probe to reference > voltage. I am not a scientist or "enjuneir" either but with a one square > metre untuned loop you can't go far wrong. > > Mike > ----- Original Message ----- From: "Alan Melia" > > To: > Sent: Friday, April 02, 2010 12:44 AM > Subject: LF: Re: E-Field Probe calibration question > > > Hi Andy maybe I dont read it right, but if that is an E-field probe it is >> not a "dipole" The input capacitance senses the voltage at two points on >> the >> wavefront. The ground plane is, I believe, irrelevant. You just need >> another >> capacitance separated from the "probe" to reference to voltage to. See >> Renato's balanced probe (www.vlf.it) In your case this is the >> car.....but >> it could be the size of a dinky toy.The area of the wavefront intercepted >> by >> the probe or the ground reference does not affect the terminal >> voltage.....as I see it.................of course I might just be wrong >> cos >> i am really a scientist not an enjuneir!! >> :-)) >> Alan >> >> ----- Original Message ----- From: "Andy Talbot" < >> andy.g4jnt@googlemail.com> >> To: >> Sent: Thursday, April 01, 2010 12:02 PM >> Subject: LF: E-Field Probe calibration question >> >> >> I have a calibrated E Field antenna (Procomm AAC-1) with a quoted >>> antenna-factor of 0.15V into 50 ohms when placed in a field of 1V/m, >>> >>> This is mounted in the centre of a car roof and fed via a bulkhead >>> >> connector >> >>> to a calibrated measuring receiver inside the vehicle, which we can >>> assume >>> is a Faraday cage at LF, S0 my question is : How is the effective >>> >> height >> >>> of the antenna changed? It was 0.15m - the specification said so - but >>> this would have been over an infinite groundplane. Do I regard the body >>> >> of >> >>> the car as being the other half of a dipole? In which case, at 1.5m it >>> >> adds >> >>> 20dB to the received signal and makes a mockery of calibrated measurement >>> >> of >> >>> the E-Field value.. >>> >>> Is it worth persuing this route, or better to stick to untuned loops for >>> calibrated E-Field measurements at LF/MF? >>> >>> >>> Andy >>> www.g4jnt.com >>> >>> >> >> > > > --00032555a08225e74504833249af Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
On the basis of two measurements out in the field -=A0the results=A0s= uggests the voltage being picked up is=A0slightly more than the effective= length as stated, but resukts for such a quick first approxiomation are= in teh right region:
=A0
At two /P monitoring sites at distances of 3.5 and 14km, the measured= power was calculated back to a field strength using the quoted antenna fa= ctor, then this E field was related to ERP using the standard equation.
=A0
At 3.5km the ERP worked out at around 200mW which isn't too far= from what I thought it was from Rloss / Rrad calculations.=A0=A0 BUT, the= Rx was surrounded by trees and a power cable close by, so could reasonabl= y be expected to be lower than it should be.
=A0
The second site was in the middle of flat land, at the=A0top of a Hil= l=A0=A0 (Lane End Down for those microwavers on this reflector), where the= re were virtually no local screening.=A0=A0 =A0ERP calculated back to 900m= W.=A0 This result is too high, suggesting the E-Field probe=A0antenna is= picking up more signal than it ought to.=A0=A0=A0 I need to make some mor= e measurements further afield, and to compare with a loop before coming to= any conclusion - but an afternoon pleasently spent getting a measurement= in the right region at least.
On 1 April 2010 13:05, Mike McAlevey <mcalevey@xtra.co.nz> wrote:
Hi Andy.
I would go along= with Alan's thinking. It's about the probe to reference voltage.= I am not a scientist or "enjuneir" either but with a one square= metre untuned loop you can't go far wrong.

Mike
----- Original Message ----- From: "Alan Melia" <= alan.melia@= btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, April 02, 2010 12:44 AM
Subject: LF: Re: E-Field Probe ca= libration question


Hi Andy maybe I dont read it= right, but if that is an E-field probe it is
not a "dipole"= The input capacitance senses the voltage at two points on the
wavefront. The ground plane is, I believe, irrelevant. You just need anoth= er
capacitance separated from the "probe" to reference to vol= tage to. See
Renato's balanced probe (www.vlf.it) =A0In your case this is the car.....bu= t
it could be the size of a dinky toy.The area of the wavefront intercepted= by
the probe or the ground reference does not affect the terminal
v= oltage.....as I see it.................of course I might just be wrong cos=
i am really a scientist not an enjuneir!!
:-))
Alan

----- Ori= ginal Message ----- From: "Andy Talbot" <andy.g4jnt@googlemail.com&g= t;
To: <= rsgb_lf_group@blacksheep.org>
Sent: Thursday, April 01, 2010 12:= 02 PM
Subject: LF: E-Field Probe calibration question


I have a calibrated E Field an= tenna (Procomm AAC-1) with a quoted
antenna-factor of 0.15V into 50 ohm= s when placed in a field of 1V/m,

This is mounted in the centre of a car roof and fed via a bulkhead
=
connector
to a calibrated measuring rece= iver inside the vehicle, which we can assume
is a Faraday cage at LF,= =A0S0 my question is : =A0 =A0How is the effective
height
of the antenna changed? =A0 = =A0It was 0.15m - the specification said so - but
this would have been= over an infinite groundplane. =A0Do I regard the body
of
the car as being the other hal= f of a dipole? =A0In which case, at 1.5m it
adds
20dB to the received signal an= d makes a mockery of calibrated measurement
of
the E-Field value..

Is= it worth persuing this route, or better to stick to untuned loops for
= calibrated E-Field measurements at LF/MF?


Andy
www.g4= jnt.com







--00032555a08225e74504833249af--