Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dd05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9FB1A38000092; Sat, 30 Jun 2012 04:16:05 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1SkspD-0005Fl-CC for rs_out_1@blacksheep.org; Sat, 30 Jun 2012 09:14:39 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1SkspC-0005Fa-Co for rsgb_lf_group@blacksheep.org; Sat, 30 Jun 2012 09:14:38 +0100 Received: from nm16-vm0.bullet.mail.ird.yahoo.com ([77.238.189.192]) by relay1.thorcom.net with smtp (Exim 4.77) (envelope-from ) id 1SkspA-0004fv-Ng for rsgb_lf_group@blacksheep.org; Sat, 30 Jun 2012 09:14:37 +0100 Received: from [77.238.189.52] by nm16.bullet.mail.ird.yahoo.com with NNFMP; 30 Jun 2012 08:14:35 -0000 Received: from [212.82.108.227] by tm5.bullet.mail.ird.yahoo.com with NNFMP; 30 Jun 2012 08:14:34 -0000 Received: from [127.0.0.1] by omp1004.bt.mail.ird.yahoo.com with NNFMP; 30 Jun 2012 08:14:34 -0000 X-DKIM-Result: Domain=btopenworld.com Result=Signature OK X-Yahoo-Newman-Id: 977860.15251.bm@omp1004.bt.mail.ird.yahoo.com Received: (qmail 37719 invoked from network); 30 Jun 2012 08:14:34 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btopenworld.com; h=DKIM-Signature:X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=Xxfz6g339JLSk7cTRgeIPl6bc7YaSh/3cz38lC6qEhUFkPwqHMM6rYb4phjMuhE+kEuPARD7VSlCnszl9D8vk4oIVb3+STTgrM0k0ks8YmtfQepljMCyP6M6zXNDFH0NzzvPt7wKbbeTaN8amOjCRgSZvsjDMHr8FjpltQgpt50= ; DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=btopenworld.com; s=s1024; t=1341044074; bh=E0+I5ZAoa+OlJkAMPY+B6gSfzYFGHT5BEBi1klpBe44=; h=X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=ulKj2t4Eqs2AL9X42MKRuFW11c1xWna7ILt3qgmbpbRivVxSn66OKZ8J4HXtkJB/jVc2+rI35YIHpRPRPBna3j+2+QYVRIJCQMRPYax/8zdDX680tSUybBnp09SlErN8uXchWzEchzn5nua+3xwdDixavsG6W/qnm6giLJ4tmuU= X-Yahoo-Newman-Property: ymail-3 X-YMail-OSG: WdmADMIVM1lNv1Ny88Oe.DkONBBY0m7nT5Oph.0DQX1_Pw2 WmsJT1Wn8YtubZg1C3JVxN2VEtWw5OB7iEiNBh8M7M0cZJCAT3WWtan92L3_ PeScUd7Phvb_EDcJGMx9bBlcBVQ22tSYDhw3D4uxS5EWTf4DnRetKMF7g138 iG_iOcUD4cdpKzYbwgJ3hXyEhtRMNLobDyEaWWHZh3SjAqqB.Ay2vlPylevf xWlkv04UoZg3FUfkWY826n1GTonFXIyBysRkQfNG8oaf69DUmkUKNHQQKOJX NhF3Z4cKDDYuuJJ1xZQQi.04Qk_M50uZFCBJsiItk0Qi8j_xj0RtQS0wddCC CjcfHmrl48S.1iIKshGADjLtQc3PJ6A8xDYFQ4B2HVY2R_AMAqpqBOdMpWJ5 9672LVplMdUtj3WutLdXoCAR8BcybbNPS X-Yahoo-SMTP: Cxhli3eswBD1ozmtAojhjrja86kWx0Qm9tycD5QR1DKWrOLgjJcXkw-- Received: from JimPC (james.moritz@86.185.202.35 with login) by smtp817.mail.ird.yahoo.com with SMTP; 30 Jun 2012 08:14:34 +0000 GMT Message-ID: From: "James Moritz" To: References: <4FEE0F7E.2090109@iup.uni-heidelberg.de> <0F87F4C0AE524B1E9EA631C81D579573@gnat> <4FEE3A73.1090602@iup.uni-heidelberg.de> In-Reply-To: <4FEE3A73.1090602@iup.uni-heidelberg.de> Date: Sat, 30 Jun 2012 09:14:41 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463 X-Spam-Score: 0.2 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Dear Stefan, LF Group, The mechanical filter consists of an array of metal disks or rods that are mechanically resonant near the centre frequency of the filter. In order to convert the electrical input and output to/from mechanical vibration, there are transducers at the input and output, sometimes piezo-electric, but in this case probably magnetostrictive. These are a coil of wire wound around magnetic material which changes shape slightly depending on the magnetic flux. So electrically, the input and output of your filter are inductors - in order to get efficient transfer of signal power into the transducers and through the filter, they must be tuned to resonance, like any LC filter circuit. If they are not correctly tuned, little power from the mechanical resonators inside the filter will be coupled to the source and load, so the resonators will have very little damping, and the filter will have large peaks in the response, as you saw. Also, the insertion loss will be higher. The same type of behaviour with mis-matched loads occurs with almost any filter - LC, crystal, ceramic, cavity, etc. A similar effect occurs if one resonator is defective - in this case the mis-match occurs inside the filter. [...] Content analysis details: (0.2 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [77.238.189.192 listed in list.dnswl.org] 0.2 STOX_REPLY_TYPE STOX_REPLY_TYPE 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay lines X-Scan-Signature: f62c7cf8eeb8e5a327b71719e9bffff1 Subject: LF: Re: Help needed, mechanical filters Content-Type: text/plain; format=flowed; charset="ISO-8859-15"; reply-type=original 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=0.1 required=5.0 tests=MISSING_OUTLOOK_NAME 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: 0:2:459325600:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d302.1 ; domain : btopenworld.com DKIM : fail x-aol-sid: 3039ac1d40914feeb5c5627d X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none Dear Stefan, LF Group, The mechanical filter consists of an array of metal disks or rods that are mechanically resonant near the centre frequency of the filter. In order to convert the electrical input and output to/from mechanical vibration, there are transducers at the input and output, sometimes piezo-electric, but in this case probably magnetostrictive. These are a coil of wire wound around magnetic material which changes shape slightly depending on the magnetic flux. So electrically, the input and output of your filter are inductors - in order to get efficient transfer of signal power into the transducers and through the filter, they must be tuned to resonance, like any LC filter circuit. If they are not correctly tuned, little power from the mechanical resonators inside the filter will be coupled to the source and load, so the resonators will have very little damping, and the filter will have large peaks in the response, as you saw. Also, the insertion loss will be higher. The same type of behaviour with mis-matched loads occurs with almost any filter - LC, crystal, ceramic, cavity, etc. A similar effect occurs if one resonator is defective - in this case the mis-match occurs inside the filter. You can probably use the input and output resonating capacitors to match your filter directly to 50R, using two capacitors in a series or shunt matching arrangement, like some have used for loop antennas. But buffer amlifiers might be needed to provide stable input and and output impedances for the filter, and provide some gain to compensate for the insertion loss. Cheers, Jim Moritz 73 de M0BMU