Return-Path: Received: from rly-de06.mx.aol.com (rly-de06.mail.aol.com [172.19.170.142]) by air-de05.mail.aol.com (v123.4) with ESMTP id MAILINDE052-4df4a1356ad2b5; Tue, 19 May 2009 21:02:54 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-de06.mx.aol.com (v123.4) with ESMTP id MAILRELAYINDE062-4df4a1356ad2b5; Tue, 19 May 2009 21:02:39 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M6aBc-0007Qj-IT for rs_out_1@blacksheep.org; Wed, 20 May 2009 02:01:36 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M6aBc-0007Qa-5Y for rsgb_lf_group@blacksheep.org; Wed, 20 May 2009 02:01:36 +0100 Received: from smtp819.mail.ird.yahoo.com ([77.238.189.19]) by relay3.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1M6aBa-0006HV-Gf for rsgb_lf_group@blacksheep.org; Wed, 20 May 2009 02:01:36 +0100 Received: (qmail 24002 invoked from network); 20 May 2009 01:01:28 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btopenworld.com; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property: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=xnVGW3EQBsb/45Qhd4N7R3R8MbQDNbKrlsJW/O1Fw6L8C72T9EGog8FMS0te4U5PhG382ZvD2bNXn2q621SAO1kSzHtGIQCGOM8ZzDRm64JHPo3P5bjan/GlWayf3A4h4lyYEGPp8k297mI9xEkBiWy55jl2RPn8sQsp1JG9ZBg= ; Received: from unknown (HELO JimPC) (james.moritz@86.177.111.34 with login) by smtp819.mail.ird.yahoo.com with SMTP; 20 May 2009 01:01:28 -0000 X-YMail-OSG: ppGREDQVM1l6Bfk0XXqH.WboWkFKAWgKJVNdpP_gaQhs89ynWvcRdoqpo_S.yyfWKm8g9z9U2yAfB0mHKveHECgiGt32hue.aENjoqkkAivN_U4XqAWef_pfKEwdkMisjD16iS0nU8ProLj0lny_S5MunhnC2bQFb9ATAjP9JK83yGgf_ne.M2_VabQPvEYFdwjyv8.SogYfKVZGAEeLkk_iDcz7EU7ygOIIl_y9CJYyHoFb31SImepu5vcfhCQrWOPWRyFFUOTkDqBHDTVYHM2_T99ZhAc.dBaWEWW.pvZjuBcNGCU- X-Yahoo-Newman-Property: ymail-3 Message-ID: From: "James Moritz" To: References: <003001c9d8c4$719e7710$6401a8c0@asus> In-Reply-To: <003001c9d8c4$719e7710$6401a8c0@asus> Date: Wed, 20 May 2009 02:01:28 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6001.18000 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6001.18049 DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: LF: Re: 518khz - Notch Filter. Content-Type: text/plain; format=flowed; charset="iso-8859-1"; 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-IP: 193.82.116.20 Dear Gary, LF Group, An image of 518kHz at 506kHz implies LO = 512kHz? You could change the LO frequency to 500kHz, although then you would not be able to receive signals on that spot frequency. You could also try optimising the amplitude/phase "tweaks" in the software to give maximum rejection of the unwanted sideband at 518kHz. A simple notch filter with high rejection will inevitably have significant loss at nearby frequencies - there is a trade-off between Q, depth of notch, loss of wanted signal and frequency difference between wanted signal and notch frequencies. This can be improved by adding aditional components, e.g. adding a series capacitor to a parallel-tuned trap can "tune out" the loss at a frequency below the notch frequency. It is feasible to get something like a few dB loss at 504kHz with 20 - 25dB at 518kHz. More complicated designs like Andy's have a much nicer response shape, but may require unachieveably high inductor Q to get the design response. Cheers, Jim Moritz 73 de M0BMU