X-GM-THRID: 1234888028149353688 X-Gmail-Labels: rsgb lf Delivered-To: daveyxm@gmail.com Received: by 10.35.22.5 with SMTP id z5cs318595pyi; Fri, 27 Apr 2007 06:36:36 -0700 (PDT) Received: by 10.78.142.14 with SMTP id p14mr887933hud.1177680996197; Fri, 27 Apr 2007 06:36:36 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.google.com with ESMTP id a1si1248986ugf.2007.04.27.06.36.33; Fri, 27 Apr 2007 06:36:36 -0700 (PDT) Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1HhQZL-0005HX-BR for rs_out_1@blacksheep.org; Fri, 27 Apr 2007 14:33:03 +0100 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1HhQZK-0005HO-HC for rsgb_lf_group@blacksheep.org; Fri, 27 Apr 2007 14:33:02 +0100 Received: from smtp804.mail.ird.yahoo.com ([217.146.188.64]) by relay2.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1HhQZI-0006Up-Mg for rsgb_lf_group@blacksheep.org; Fri, 27 Apr 2007 14:33:02 +0100 Received: (qmail 56100 invoked from network); 27 Apr 2007 13:32:54 -0000 Received: from unknown (HELO MJUSonyLaptop) (m.j.underhill@btinternet.com@86.142.235.125 with login) by smtp804.mail.ird.yahoo.com with SMTP; 27 Apr 2007 13:32:53 -0000 X-YMail-OSG: hKLgic4VM1m2nD6tYeDX4U1zcQ6GI4pWrFh.K8WxUojwDaXNsYyGqK93ek5kf5fCOiRdVArB1mBkCkadTrf5iGCS_JtTQbK0kxlB6eNcLEH34cXB From: "Mike Underhill" To: Date: Fri, 27 Apr 2007 14:33:10 +0100 Message-ID: <000c01c788d0$996a3cc0$6405a8c0@MJUSonyLaptop> MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6822 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 In-Reply-To: Thread-Index: AceIwLJP6Bu/ihvVQlSQVCcNLuIYyQADHhlA Importance: Normal X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: RE: Filter expert needed - Mystery of the lost real zero. Content-Type: multipart/alternative; boundary="----=_NextPart_000_000D_01C788D8.FB31B200" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.3 required=5.0 tests=HTML_50_60, HTML_FONTCOLOR_UNKNOWN,HTML_MESSAGE 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 Status: O X-Status: X-Keywords: X-UID: 2011 This is a multi-part message in MIME format. ------=_NextPart_000_000D_01C788D8.FB31B200 Content-Type: text/plain; charset="windows-1250" Content-Transfer-Encoding: quoted-printable Andy=20 =20 For a second zero on the HF side try an inductor across the =91zero=92 capacitor. The trouble is that it will have to have the same reactance = as this 1.5p capacitor and that may not be easily realisable in practice. = The inductor could also go between resonators 1 and 3 or 3 and 5 I think. = If the inductor value is too high you can use a small =91link=92 coil on = each of the resonators to be inductively coupled and connect these by a pair of twisted wires. Getting the coupling right can be fiddly. You can get another LF zero rather than the wanted HF zero, I think, if you get the phasing wrong. =20 =20 I hope this helps but it is some time since I taught this stuff. Good = luck. =20 Mike =96 G3LHZ =20 =20 =20 From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Andy Talbot Sent: 27 April 2007 12:36 Subject: LF: Filter expert needed - Mystery of the lost real zero. =20 Is there anyone monitoring these groups/reflector who knows the deep = insides of filter design theory? =20 I've just synthesized a straightforward 50- 75MHz 5th order = Top-C-coupled bandpass filter to form part of a frequency converter that will feed an SDR-IQ digital receiver. While playing with the filter design using a circuit analysis package, and recalling satellite microwave cavity = filter designs from the dim-and-distant past, I remembered that by arranging cross-coupling between non adjacent resonators, it was possible to form pairs of real zeros in the upper and lower stop bands respectively. = These convert the filter to an elliptic type response, and considerably = improve the cut-off. I also recall it was a very critical thing to set up. =20 =20 So, I tried adding an additional cap between resonators 2 and 4, got a wonderful 10 - 20dB improvement in the low end cut-off response around = 40MHz exactly where it was needed, BUT ONLY THE ONE REAL-ZERO COULD BE FOUND = !!! There is absolutely no sign af any second null above the passband.=20 =20 Where's it gone? Shouldn't they always come in pairs? This is really bugging me, I can't sleep at night, can anyone explain? =20 Could it be because a top-coupled - C BPF is non-symmetrical? =20 Full circuit details can be found at HYPERLINK "http://www.scrbg.org/g4jnt/50-75bpf.pdf"http://www.scrbg.org/g4jnt/50-75= bpf .pdf =20 Andy G4JNT HYPERLINK "http://www.scrbg.org/g4jnt"www.scrbg.org/g4jnt No virus found in this outgoing message. Checked by AVG Free Edition.=20 Version: 7.5.463 / Virus Database: 269.6.1/777 - Release Date: = 26/04/2007 15:23 =20 ------=_NextPart_000_000D_01C788D8.FB31B200 Content-Type: text/html; charset="windows-1250" Content-Transfer-Encoding: quoted-printable

Andy

 

For a second zero on the HF side = try an inductor across the =91zero=92 capacitor.  The trouble is that it will have to have the same reactance as this 1.5p capacitor and that may = not be easily realisable in practice.  The inductor could also go between resonators 1 and 3 or 3 and 5 I think.  If the inductor value is = too high you can use a small =91link=92 coil on each of the resonators to be inductively coupled and connect these by a pair of twisted wires.  = Getting the coupling right can be fiddly. You can get another LF zero rather = than the wanted HF zero, I think, if you get the phasing wrong.  =

 

I hope this helps but it is some = time since I taught this stuff. Good luck.

 

Mike =96 G3LHZ

 

 

 


From: = owner-rsgb_lf_group@blacksheep.or= g [mailto:owner-rsgb_lf_group@blacksheep.or= g] On Behalf Of Andy = Talbot
Sent: 27 April 2007 12:36
 Subject: LF: Filter = expert needed - Mystery of the lost real zero.

 

Is there anyone monitoring these groups/reflector who knows the = deep insides of filter design theory?

 

I've just synthesized a straightforward 50- 75MHz 5th order Top-C-coupled  bandpass filter to form part of a = frequency converter that will feed an SDR-IQ digital receiver.   = While playing with the filter design using a circuit analysis = package, and recalling satellite microwave cavity filter designs from the dim-and-distant past, I remembered that by arranging cross-coupling = between non adjacent resonators, it was possible to form pairs of real zeros in = the upper and lower stop bands respectively.  These convert the = filter to an elliptic type response, and considerably improve the cut-off.  I = also recall it was a very critical thing to set up.   =

 

So, I tried adding an additional cap between resonators 2 and 4, = got a wonderful 10 - 20dB improvement in the low end cut-off response around = 40MHz exactly where it was needed,  BUT ONLY THE ONE REAL-ZERO COULD BE = FOUND !!!  There is absolutely no sign af any second null above the = passband.

 

Where's it gone?  Shouldn't they always come in pairs?  This is really bugging me, I can't sleep at = night, can anyone explain? 

Could it be because a top-coupled - C  BPF is = non-symmetrical?

 

Full circuit details can be found at    http://www.scrbg.org/g4j= nt/50-75bpf.pdf

 

Andy  G4JNT


No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.463 / Virus Database: 269.6.1/777 - Release Date: = 26/04/2007 15:23

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