Return-Path: Received: (qmail 23772 invoked from network); 16 Dec 2002 13:14:26 -0000 Received: from murphys.services.quay.plus.net (212.159.14.225) by mailstore with SMTP; 16 Dec 2002 13:14:26 -0000 Received: (qmail 11587 invoked from network); 16 Dec 2002 13:13:51 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by murphys.services.quay.plus.net with SMTP; 16 Dec 2002 13:13:51 -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 18Nv3l-0004js-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 16 Dec 2002 13:13:25 +0000 Received: from [213.218.77.56] (helo=cmailENV4.svr.pol.co.uk) by post.thorcom.com with esmtp (Exim 4.10) id 18Nv3l-0004jj-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Dec 2002 13:13:25 +0000 Received: from [62.21.144.179] (helo=w8k3f0.freeler.nl) by cmailENV4.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 18Nv3j-0007Wq-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Dec 2002 13:13:24 +0000 Message-ID: <5.1.0.14.0.20021216134838.00ac2c50@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Mon, 16 Dec 2002 14:14:58 +0100 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <18NsUL-1YFOL2C@fwd02.sul.t-online.com> References: <5.1.0.14.0.20021215145628.00a2ba10@POP3.freeler.nl> MIME-Version: 1.0 Subject: Re: LF: Measuring earth resistance Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=-1.0 required=5.0tests=BIG_FONT,IN_REP_TO,QUOTED_EMAIL_TEXT,REFERENCES, 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

I wrote:

................
> Measuring earth resistance at 50Hz has no meaning for the loss at 136kHz
> because the earth resistance (impedance is more correct) is frequency
> dependent.

Upon this Uwe, DJ6WX, remarked:

but you use a noise source ie. not 136kHz only. does that not matter ?

The noise source indeed produces noise over a wide band of frequencies. But as a detector a receiver is used and therefore only a small frequency band around 136kHz is used to balance the bridge. The width of that band depends on the pass band of the receiver. Because the bridge can theoretically be balanced for one frequency component of the noise only it is necessary to use as small a bandwidth as possible. With a wide pass band of the receiver a minimum in the noise can still be found but it is not very pronounced. So the narrower the pass band of the receiver, the deeper the noise minimum becomes.

73, Dick, PA0SE