Return-Path: Received: (qmail 16548 invoked from network); 10 May 2001 11:27:29 -0000 Received: from unknown (HELO guinness.servers.plus.net) (212.159.3.230) by excalibur.plus.net with SMTP; 10 May 2001 11:27:29 -0000 Received: (qmail 3362 invoked from network); 10 May 2001 08:24:29 -0000 Received: from post.thorcom.com (212.172.148.70) by mx.last.plus.net with SMTP; 10 May 2001 08:24:29 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.16 #2) id 14xls1-00051U-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 10 May 2001 09:32:25 +0100 Received: from rubellite.lion-access.net ([212.19.217.4]) by post.thorcom.com with esmtp (Exim 3.16 #2) id 14xls0-00051P-00 for rsgb_lf_group@blacksheep.org; Thu, 10 May 2001 09:32:24 +0100 Received: from w8k3f0 (1Cust175.tnt8.rtm1.nl.uu.net [213.116.110.175]) by rubellite.lion-access.net (I-Lab) with SMTP id 5DBE827DF for ; Thu, 10 May 2001 08:31:31 +0000 (GMT) Message-ID: <004401c0d92c$0f19a060$af6e74d5@w8k3f0> From: "Dick Rollema" To: rsgb_lf_group@blacksheep.org References: <65AECDF1F89AD411900400508BFC869F9C0491@pdw-mail-1.dera.gov.uk> <3AFA2E4C.EBB3C4EF@alg.demon.co.uk> Subject: Re: LF: Antenna Current Date: Thu, 10 May 2001 10:05:08 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2314.1300 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: To All from PA0SE Andy G4JNT wrote: > > I also suggest that the different current measured at each end of a > > loading coil, as mentioned in an earlier posting, could quite easily be > > due to the slight mistuning when the extra hardware associated with the > > ammeter is connected in circuit on the top side. Steve, GW4ALG, responded: > As mentioned in my earlier posting, I was careful to check for > system resonance before each measurement. How about you, Dick? The effect Andy mentions is indeed present. Apart from the thermo couple ammeter that I moved from top to bottom of the coil there is another instrument permanent in place at the top end. Inserting the second meter in series caused the aerial current to drop from 2A to 1.85A. But a slight retune restored it to 2A again. Also when measuring the current of 2.1A at the bottom end, the instrument at the top still indicated the same 2A. In my former e-mail I said the difference was 10%; it is 5% of course. Modelling showed that a difference of 1.55% is caused by the "normal" capacitive current that leaves the coil as part of the near field around the aerial as the coil is part of the radiating system. The remaining part must be extra capacitive current flowing to earthed objects surrounding the coil. To check this I moved the coil upwards and sideways in the shack and expected this would at least cause a small change in the current difference between top and bottom of he coil. But no, there was no detectable change at all. So I'm afraid I still don't quite understand the situation. 73, Dick, PA0SE