Return-Path: Received: (qmail 7412 invoked from network); 24 Jan 2003 15:20:06 -0000 Content-Transfer-Encoding: 8bit Received: from netmail02.services.quay.plus.net (212.159.14.221) by mailstore with SMTP; 24 Jan 2003 15:20:06 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 5199 invoked by uid 10001); 24 Jan 2003 15:20:06 -0000 Received: from post.thorcom.com (193.82.116.70) by netmail02.services.quay.plus.net with SMTP; 24 Jan 2003 15:20:06 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.12) id 18c5cE-0007vr-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 24 Jan 2003 15:19:34 +0000 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.12) id 18c5cE-0007vi-00 for rsgb_lf_group@blacksheep.org; Fri, 24 Jan 2003 15:19:34 +0000 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 18c5c4-00020w-00 for rsgb_lf_group@blacksheep.org; Fri, 24 Jan 2003 15:19:24 +0000 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 18c5c2-0005HC-00 for rsgb_lf_group@blacksheep.org; Fri, 24 Jan 2003 15:19:22 +0000 Message-ID: <5.1.0.14.0.20030124142752.00aed8b8@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Fri, 24 Jan 2003 15:19:19 +0000 To: rsgb_lf_group@blacksheep.org From: "James Moritz" In-reply-to: MIME-Version: 1.0 X-MailScanner: No Virus detected Subject: Re: LF: AW: VFO for VLF receiver? Digital type pre-mixer, any ideas? Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=0.4 required=6.0tests=DEAR_SOMEBODY,IN_REP_TO,SPAM_PHRASE_03_05version=2.43 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rsgb_lf_group-outgoing@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Dear Jan-Martin, LF group At 11:37 24/01/2003 +0100, you wrote: >Suppose I could use an FF, preferably CD4013 for the mixer. > >But I can't find any reference to similar constructions, only have a vague >memory that it has been mentioned in TT some time in the last 35 years A D-type flip-flop does work something like a mixer. If you feed 1MHz into the clock input, and 1.001MHz square wave into the D input, the output will approximately be a 1kHz square wave. The interesting thing is that you will also get the 1kHz square wave if the D input is 0.001, 0.999, 1.999, 2.001, 2.999, 3.001... nMHZ +/-1kHz. The D-type flip-flop effectively "samples" the logic level at the D input the moment the clock transition occurs - it works like a sample-and-hold with a square wave input, and no anti-aliasing filter (this analogue scheme is used in things like sampling scopes, modulation meters, vector voltmeters, etc., or optically with a stroboscope). The trouble is that, since it is effectively mixing the square wave input with a train of impulses at the clock frequency, and low pass filtering the result, the output spectrum contains many harmonic and non-harmonic components as well as the desired output. These are easy to filter out if the difference frequency is much smaller than either input frequency, but if you try to use the sum frequency output, or the output frequency is comparable to the input frequency, the output waveform is roughly a square wave but with substantial pulse-width modulation, which would be difficult to filter to get a clean VFO signal. So for your mixer-VFO, a conventional mixer would work better. Cheers, Jim Moritz 73 de M0BMU