Return-Path: Received: (qmail 21861 invoked from network); 16 Dec 2002 13:14:25 -0000 Received: from marstons.services.quay.plus.net (212.159.14.223) by mailstore with SMTP; 16 Dec 2002 13:14:25 -0000 X-Priority: 3 Received: (qmail 14617 invoked by uid 10001); 16 Dec 2002 13:13:53 -0000 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by marstons.services.quay.plus.net with SMTP; 16 Dec 2002 13:13:52 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 18Nv3i-0004jf-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 16 Dec 2002 13:13:22 +0000 Received: from [213.218.77.56] (helo=cmailENV4.svr.pol.co.uk) by post.thorcom.com with esmtp (Exim 4.10) id 18Nv3h-0004jW-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Dec 2002 13:13:21 +0000 Received: from [62.21.144.179] (helo=w8k3f0.freeler.nl) by cmailENV4.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 18Nv3g-0007Wq-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Dec 2002 13:13:20 +0000 Message-ID: <5.1.0.14.0.20021216132519.00acad40@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Mon, 16 Dec 2002 13:45:58 +0100 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <2D280BB697C7EE4C979C5C89925418EF368FDC@TNS-FBU-2E-003.corp .telenor.no> MIME-Version: 1.0 Subject: Re: LF: Measuring earth resistance Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=-1.1 required=5.0tests=BIG_FONT,EMAIL_ATTRIBUTION,IN_REP_TO,MAILTO_LINK, SPAM_PHRASE_00_01version=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Content-transfer-encoding: 8bit To All from PA0SE

Jan-Martin, LA8AK. wrote:

but suppose the values of the noise generator are for the range 3-30MHz, the coupling capacitors must be increased for VLF

The noise bridge was indeed not designed for LF but there is plenty of noise on LF and the bridge can be perfectly nulled on 136kHz. But the X-control has hardly any effect as its range is from 190pF till -155pF (means inductive reactance) and that amounts to -j6.15 kohm till j7.54 kohm as minimum values that can be measured in parallel with Rx. But for measuring earth resistance the X-control is not used because I bring the aerial system into resonance so that only a pure ohmic resistance has to be measured.

To make the X-control useful on LF it might be better to connect C1 in series with R3 and C2 in series with Zx; but I have not investigated that. I used the parallel version because at high frequencies it is easier to compensate for the parasitic capacitances of R3 and C2.

73, Dick, PA0SE

-----Opprinnelig melding-----
Fra: WarmSpgs@aol.com [mailto:WarmSpgs@aol.com]
Sendt: 15. desember 2002 21:29
Til: rsgb_lf_group@blacksheep.org
Emne: Re: LF: Measuring earth resistance

Dick Rollema's noise bridge schematic and a photo of his assembled unit can
now be downloaded from:

http://lwca.org/library/articles/pa0se/earth/

73
John Davis