Return-Path: Received: (qmail 21207 invoked from network); 9 Jan 2001 11:10:51 -0000 Received: from unknown (HELO warrior-inbound.servers.plus.net) (212.159.14.227) by 10.226.25.101 with SMTP; 9 Jan 2001 11:10:51 -0000 Received: (qmail 26788 invoked from network); 9 Jan 2001 11:14:11 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior with SMTP; 9 Jan 2001 11:14:11 -0000 Content-Transfer-Encoding: 8bit Received: from majordom by post.thorcom.com with local (Exim 3.16 #1) id 14FwaK-0002ia-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 09 Jan 2001 11:05:00 +0000 Received: from bob.dera.gov.uk ([192.5.29.90]) by post.thorcom.com with esmtp (Exim 3.16 #1) id 14FwaJ-0002iV-00 for rsgb_lf_group@blacksheep.org; Tue, 09 Jan 2001 11:04:59 +0000 X-Priority: 3 X-MSMail-Priority: Normal Received: by bob.dera.gov.uk; (8.8.8/1.3/10May95) id LAA07315; Tue, 9 Jan 2001 11:05:56 GMT Received: (qmail 18771 invoked from network); 9 Jan 2001 11:59:02 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from gauntlet.mail.dera.gov.uk (172.16.9.10) by baton.dera.gov.uk with SMTP; 9 Jan 2001 11:59:02 -0000 Received: by gauntlet.mail.dera.gov.uk; id LAA07160; Tue, 9 Jan 2001 11:51:35 GMT Received: from unknown(10.71.64.31) by gauntlet.mail.dera.gov.uk via smap (3.2) id xma007084; Tue, 9 Jan 01 11:50:59 GMT Received: from frn-gold-1.dera.gov.uk (unverified) by mailguard.dera.gov.uk (Content Technologies SMTPRS 4.1.5) with ESMTP id for ; Tue, 9 Jan 2001 11:06:57 +0000 Received: by frn-gold-1.dera.gov.uk with Internet Mail Service (5.0.1460.8) id ; Tue, 9 Jan 2001 11:04:11 -0000 Message-ID: <65AECDF1F89AD411900400508BFC869F0D74F5@pdw-mail-1.dera.gov.uk> From: "Talbot Andrew" To: rsgb_lf_group@blacksheep.org Subject: LF: RE: LF Receiver Date: Tue, 9 Jan 2001 11:04:15 -0000 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.0.1460.8) Content-Type: text/plain; charset=iso-8859-1; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Sorry - I misunderstood, thought you were trying to digitally downconvert directly ! Yes, that would work quite well. In fact G4GUO did just that on 73kHz a few years ago using the 56002EVM with left and right channels for I/Q and a downconverter fed with quadrature square waves in a mixer made from 4066 analogue gates. There is no need for a DDS with quadrature outputs, switching mixers works best if driven from a clean square wave. The LF input has to be filtered to remove frequencies mixing with the third harmonic of the LO, which of course would have to be done with any mixer type - again the 100dB attenuation at 1MHz freqs, you can't get away from that so easily ! One problem is the 3kHz (or whatever) lowpass filters. These have to be analogue and very very precisely matched to preserve the 90 degree phase relationship. Switched capacitor designs, such as used on the Codec input, will work to an extent, but even these require some analogue filtering to remove frequencies interfering THEIR alias products. I'm not really a proponent of wide band digitisation then subsequently filtering, unless that is really what you want and need for simultaneous band monitoring purposes. Better to optimise gain / dynamic range, analogue filter to a few 100 Hz bandwidth then digitise at a lower rate. Andy G4JNT > perhaps I didn't make myself clear. What I > was suggesting was not > to digitize directly at 136 kHz. > My idea is along the following line : > Using a DDS with quadrature outputs (AD9854, if memory > serves), feed the > two signals to two mixers, each of them gets also the wanted > RF (in phase).> -- The Information contained in this E-Mail and any subsequent correspondence is private and is intended solely for the intended recipient(s). For those other than the recipient any disclosure, copying, distribution, or any action taken or omitted to be taken in reliance on such information is prohibited and may be unlawful.