Return-Path: Received: (qmail 17673 invoked from network); 31 Oct 2001 09:21:56 -0000 Received: from unknown (HELO warrior.services.quay.plus.net) (212.159.14.227) by excalibur.plus.net with SMTP; 31 Oct 2001 09:21:56 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 130 invoked from network); 31 Oct 2001 09:20:38 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior.services.quay.plus.net with SMTP; 31 Oct 2001 09:20:38 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 15yrQC-000441-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 31 Oct 2001 09:12:28 +0000 Received: from imo-d06.mx.aol.com ([205.188.157.38]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 15yrQA-00043v-00 for rsgb_lf_group@blacksheep.org; Wed, 31 Oct 2001 09:12:26 +0000 Received: from DL4YHF@aol.com by imo-d06.mx.aol.com (mail_out_v31_r1.8.) id l.d1.eb6f0be (4461) for ; Wed, 31 Oct 2001 04:11:19 -0500 (EST) From: DL4YHF@aol.com Message-ID: Date: Wed, 31 Oct 2001 04:11:19 EST Subject: Re: LF: Multi-layer loading coils To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 Content-Type: text/html; charset=windows-1252 X-Mailer: AOL 6.0 for Windows DE sub 10504 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Content-transfer-encoding: 8bit Hello Ha-Jo and LF group,


> It seems that the metal of the inner coil increases the loss
> of the outer coil (and possibly vice versa).

Exactly that's what I found in own experiments.

By "forcing" the magnetic field through any kind of metal, you increase the losses.
For the same reason, long coils shouldn't be wound too closely, which is especially true when using enameled copper wire. Some of the mag field lines don't run through the full length of the coil, but 'escape' to the  sides. Forcing them through the very thin gap between the copper seems to cause additional loss. Using a calculation program for single-layer coils (like COILS.EXE from an old ARRL handbook) you can see the effect, and it can be verified in practice.

73,  Wolf   DL4YHF.