Return-Path: Received: (qmail 11713 invoked from network); 30 May 1999 03:52:35 +0100 Received: from magnet.plus.net.uk (HELO magnet.force9.net) (195.166.128.26) by guiness.force9.net with SMTP; 30 May 1999 03:52:35 +0100 Received: (qmail 12547 invoked from network); 30 May 1999 02:56:17 -0000 Received: from punt.unica.co.uk (194.75.183.60) by magnet.plus.net.uk with SMTP; 30 May 1999 02:56:17 -0000 Received: from troy.blacksheep.org ([194.75.183.50] ident=root) by punt.unica.co.uk with esmtp (Exim 2.00 #2) id 10nvek-0002LW-01; Sun, 30 May 1999 03:48:58 +0100 Received: (from root@localhost) by troy.blacksheep.org (8.6.12/8.6.12) id CAA06770 for rsgb_lf_group-outgoing; Sun, 30 May 1999 02:45:55 GMT X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (root@post.unica.co.uk [194.75.183.70]) by troy.blacksheep.org (8.6.12/8.6.12) with ESMTP id CAA06766 for ; Sun, 30 May 1999 02:45:52 GMT Received: from ns.light-house.net ([206.152.252.2] helo=light-house.net ident=root) by post.thorcom.com with esmtp (Exim 2.04 #3) id 10nvqN-0002i4-00 for rsgb_lf_group@blacksheep.org; Sun, 30 May 1999 04:00:59 +0100 Received: from sault.com (asdet1-12.light-house.net [208.171.136.14]) by light-house.net (8.8.5/8.8.5) with ESMTP id WAA17091 for ; Sat, 29 May 1999 22:29:43 -0400 (EDT) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <3750A699.24CD4FAA@sault.com> Date: Sat, 29 May 1999 22:46:49 -0400 From: "Rod Mayward" X-Mailer: Mozilla 4.51 [en]C-NECCK (Win98; I) X-Accept-Language: en MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org Subject: Re: LF: Rx converter performance. References: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org Hi David Do you have any info on your converter, i.e. a schematic and source of parts? Thanks Rod KL7RG/8 G0MRF@aol.com wrote: > > I was pleased to hear Roger's 73kHz beacon on air earlier in the week. > Although a little down on its usual level, I was suspicious that my converter > wasn't performing as well as it does on 136k. > > Using Roger's beacon and some transmissions on 136 as test sources, I > discovered that my receiver was being "de-sensed" by the level of local > oscillator feedthrough. > > The converter upconverts the LF band to an IF of 10MHz. Unfortunately the > closer you get to "10MHZ" the lower the performance. 136 is OK but 73 was > poor in comparison. > > As I have already fitted a multi turn pot to optimise carrier balance on the > MC1496, I appeared to need a very narrow filter on the output. normal coils > / caps were no use, but the answer came in the form of an 86 pence 10MHz > ceramic resonator from RS components. > > I fitted two small ferrite transformers with a 1:9 and 9:1 ratio back to back > on the output of the converter. From the centre point (at 350 Ohms) I > connected the resonator in series with a 65pF variable to ground. Listening > to the 10MHz breakthrough and tuning the capacitor I managed to reduce the > level by 27 - 28dB. > > The performance on both bands has been improved. MDS on 136 has been > improved by about 1 -2 dB, but 73k is 10dB better than before! > > The technique could be useful to anyone trying to build a robust RX (DL) > using high level diode ring mixers. > > resonant frequency of the "notch filter" could be set anywhere from 9.6 MHz > to 10.05MHz. > > 73 > > David