Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dk02.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9F6913800008C; Thu, 12 Jan 2012 06:03:47 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1RlIQr-0006xc-GM for rs_out_1@blacksheep.org; Thu, 12 Jan 2012 11:02:57 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1RlIQr-0006xT-4W for rsgb_lf_group@blacksheep.org; Thu, 12 Jan 2012 11:02:57 +0000 Received: from smtpout1.wanadoo.co.uk ([80.12.242.29] helo=smtpout.wanadoo.co.uk) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1RlIQo-0001X9-WB for rsgb_lf_group@blacksheep.org; Thu, 12 Jan 2012 11:02:57 +0000 Received: from youry0mkaz8jaq ([95.144.116.154]) by mwinf5d03 with ME id Lb2o1i00U3Kwtzz03b2oKh; Thu, 12 Jan 2012 12:02:49 +0100 Message-ID: <00e101ccd119$b7755790$ae01a8c0@youry0mkaz8jaq> From: "Martin Evans" To: References: <593F4C0651144C339855AFC49ED4329E@computereebf79> <1326365524.91314.YahooMailNeo@web28108.mail.ukl.yahoo.com> Date: Thu, 12 Jan 2012 11:02:45 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1807 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: Tuning inductance for 137kHz receive. Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:361436704:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1db4064f0ebe1330b6 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none Morning, Pete. Thanks for this. Yes, this is what I should do. My problem is that I get carried away - I begin by thinking of making a variometer - then I decide that it *must* be the biggest one ever - so I search for a *huge* former - which I can't find - and so it goes. Pathetic really. Maybe my resolution for 2012 should be to stop daydreaming and actually *do* something! Martin GW3UCJ. ######################################## Just make a variometer two inductors one inside the other like piston and cylinder and adjust in and out to resonance (I think this design is the simplest form of variometer mechanically). I use a couple of plastic paint buckets, mine are 200mm diameter. 3mH looks about right for the antenna described but fine inductance adjustment is necessary and it is best to get as high a 'Q' as you can. The band is very narrow and 'Q' helps reduce out of band high power signals. I am in fact describing my TX setup the primary inductor is a large 600mm diameter coil tapped. All my inductors are air cored. For RX you can tune the inductor with a large variable capacitor strapped across because there are no flash over issues. It is quite simple to make these tuning coils from scratch a lot of wire though, but I would recommend it. Try Rick Strobbe ON7YD's site highly recommended http://www.strobbe.eu/on7yd/136ant/#Introduction Hope this helps. 73 es GL Pete M0FMT IO91UX