Return-Path: Received: (qmail 6935 invoked from network); 23 Oct 2001 09:54:44 -0000 Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 23 Oct 2001 09:54:44 -0000 Received: (qmail 24243 invoked from network); 23 Oct 2001 09:54:27 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys with SMTP; 23 Oct 2001 09:54:27 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 15vyAU-0006NJ-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 23 Oct 2001 10:48:18 +0100 Received: from fortress.tele2.co.uk ([212.19.64.194] helo=mail.internal.tele2.net.uk) by post.thorcom.com with esmtp (Exim 3.33 #2) id 15vyAS-0006NE-00 for rsgb_lf_group@blacksheep.org; Tue, 23 Oct 2001 10:48:16 +0100 Received: from martin (wireless-066-114.tele2.co.uk [212.19.66.114]) by mail.internal.tele2.net.uk (Postfix) with SMTP id 5B8E7400CD for ; Tue, 23 Oct 2001 10:44:36 +0100 (BST) Message-ID: <000501c15ba7$ee820910$3100a8c0@martin> From: "M0MGM" To: rsgb_lf_group@blacksheep.org References: <200110230510_MC3-E442-2852@compuserve.com> Subject: LF: Re: Loading coils and shorted turns Date: Tue, 23 Oct 2001 10:48:54 +0100 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 6.00.2479.0006 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: My experiance of shorted turns on recording heads and transformers is that form a low impedance short that effectivly kills the inductor. Hello Martin, >In Peter Dodd's book LF experiments page 55 a drawing is shown of a loading >coil arrangment. The the coil inductance is adjusted by shorting turns on >the coil. Is this right? > >Martin ... not having Peter's book on hand, but there are several ways of adjusting the loading coil. The option of shorting turns on the coil can only give a rough adjustment of the inductivity needed. You can for example build a variometer. If you have a look at may homepage (http://www.qru.de/station.htm) you can see that I use a combination the method described above with a variometer inside my loading coil. In the middle of the page you can see the arrangment, a PVC tube with a smaller coil wound on it, parallel to the main coil. This allows a very definite fine adjustment of the inductance needed. If you do not have an RF meter on hand, it also helps to use an oscilloscope and put the wires of the oscilloscope near the top of the coil (do not directly connect it, you might have several thousand Volts there!) and tune for maximum voltage that you can see on the scope. I use a very simple and cheap scope to do this, which also gives me an indication about the waveform. Others have used two cylindrical coils that are being pushed into each other to fine-tune the inductivity. Walter, DJ2LF uses a lareg PVC pipe and has a small ferrit core lying inside, the position of this small core inside the pipe adjusts his inductivity. Be aware, that adjusting the loading coil is the key to get the antenna resonating, it can take a fraction of a turn with the variometer to find the resonance. Also, as an additional hint: think BIG! If you look to the loading coil I use in relation to the CD, you see, how big the coil should be. 40 cm in diamter and 50 or 60 cm length is not too big. Copper wire or litz wire might be fine, I myself used simple 1.5 square-millimeter wire used normally for electrical installations in houses, I used about 150 to 200 m for my coil. Hope this helps a bit. Best 73 Geri, DK8KW (W1KW)