Return-Path: Received: (qmail 20021 invoked from network); 2 Oct 1999 08:40:21 +0100 Received: from unknown (HELO magnet.force9.net) (195.166.128.26) by guiness.force9.net with SMTP; 2 Oct 1999 08:40:21 +0100 Received: (qmail 1353 invoked from network); 2 Oct 1999 07:45:59 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by magnet.plus.net.uk with SMTP; 2 Oct 1999 07:45:59 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 11XJQT-0002w2-00 for rsgb_lf_group-outgoing@blacksheep.org; Sat, 02 Oct 1999 08:17:49 +0100 Received: from typhoon.mail.pipex.net ([158.43.128.27]) by post.thorcom.com with smtp (Exim 3.02 #1) id 11XJQS-0002vx-00 for rsgb_lf_group@blacksheep.org; Sat, 02 Oct 1999 08:17:48 +0100 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 16308 invoked from network); 2 Oct 1999 07:17:45 -0000 Received: from userb169.uk.uudial.com (193.149.71.152) by smtp.dial.pipex.com with SMTP; 2 Oct 1999 07:17:45 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 From: "Nick" To: rsgb_lf_group@blacksheep.org Subject: Re: LF: re Dave's Comment on filters Date: Sat, 02 Oct 1999 08:18:45 +0100 Message-ID: References: <004801bf0c5b$78aca1c0$23088cd4@default> In-reply-to: <004801bf0c5b$78aca1c0$23088cd4@default> X-Mailer: Forte Agent 1.6/32.525 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: On Fri, 1 Oct 1999 21:31:05 +0100, you wrote: > Am I missing something? or >am I maybe not sufficiently practiced to take full advantage of the >difference? Hi I've been lurking here for a while but am not active on LF (yet). I do make my living out of EMC measurement and trouble shooting though so have a fair idea of noise and signal performance, The theoretical improvements are those that would take place against random noise, not close spaced strong signals, so if static and atmospheric noise were the limiting factor then what you say is true. If on the other hand strong local signals were the problem then nose bandwidth, skirt shape/depth, and stop band are critical in keeping them out to be able to hear the ones you want and the improvement because of a reduction in the adjacent signal can be much greater than the figures mentioned. When you have spectrogram on the end the actual bandwidth you are looking at the signal through is that of the FFT process and is MUCH narrower than the receiver filter. In this case the rx bandwidth is only a 'roofing filter' and, provided all the chunk of signal arriving is around the same signal level, the rx bandwidth is irrelevant. If there are strong signals coming and going within the passband however this will cause AC pumping and all sorts of problems associated with that. In this case a narrower bandwidth would help a lot if it kept the unwanted strong signals out. Hopefully my understanding of the situation actually ties up with what people observe on the band, any comments welcome. Nick (G4WHO)