Return-Path: Received: (qmail 9581 invoked from network); 15 Apr 1999 09:27:28 -0000 Received: from magnus.plus.net.uk (HELO magnus.force9.net) (195.166.128.27) by medusa.plus.net.uk with SMTP; 15 Apr 1999 09:27:28 -0000 Received: (qmail 31006 invoked from network); 15 Apr 1999 09:27:01 -0000 Received: from post.thorcom.com (194.75.130.70) by magnus.plus.net.uk with SMTP; 15 Apr 1999 09:27:01 -0000 Content-Transfer-Encoding: 8bit Received: from troy.blacksheep.org ([194.75.183.50] ident=root) by post.thorcom.com with esmtp (Exim 2.04 #3) id 10XiO0-0003fb-00; Thu, 15 Apr 1999 10:24:40 +0100 Received: (from root@localhost) by troy.blacksheep.org (8.6.12/8.6.12) id JAA17529 for rsgb_lf_group-outgoing; Thu, 15 Apr 1999 09:23:11 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 JAA17525 for ; Thu, 15 Apr 1999 09:23:08 GMT Received: from mailserv.cc.kuleuven.ac.be ([134.58.8.44]) by post.thorcom.com with esmtp (Exim 2.04 #3) id 10XiMD-0003f0-00 for rsgb_lf_group@blacksheep.org; Thu, 15 Apr 1999 10:22:50 +0100 Received: from LCBD15.fys.kuleuven.ac.be (LCBD15.fys.kuleuven.ac.be [134.58.80.15]) by mailserv.cc.kuleuven.ac.be (8.9.0/8.9.0) with SMTP id LAA07787 for ; Thu, 15 Apr 1999 11:27:17 +0200 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Message-ID: <3.0.1.16.19990415102102.2f2fb344@mail.cc.kuleuven.ac.be> X-Sender: pb623250@mail.cc.kuleuven.ac.be X-Mailer: Windows Eudora Pro Version 3.0.1 (16) Date: Thu, 15 Apr 1999 10:21:02 To: rsgb_lf_group@blacksheep.org From: "Rik Strobbe" Subject: Re: LF: Receiving In-reply-to: References: <01BE8662.1101CC00@pc033hk.hk.cro.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org At 15:44 14/04/99 +0200, DJ1ZB wrote: >If a receiver needs some input attenuation at LF on large aerials, as reported >by ON7YD on his TS440, for instance, the better way should be to realize this >"attenuation" by the loss of a simple coil filter using one to four resonant >circuits. But such an arrangement would need less resistive attenuation to stop >the overload of the receiver, therefore even some additional preamplification >(and selectivity) might be possible, with resonant circuits carefully arranged >ahead and behind amplification so that in an empty band the S-meter hangs >around "S1". Then it should even be possible to receive the commercial LF >stations with an indication of S9+30dB if the receiver has sufficient AGC >range. Resonant circuits have the advantage to attenuate out-of-the-band signals selective. But to my experience it can have 2 'hooks' : 1. Attenuation of close to the band signals (eg. DBF39 / DCF39) is minimal 2. When using unsuitable ferrites these filtere can even create intermodulation-signals themselves I did some experiments with bandpass filters but at the end a simple attenuator did the best job (with me) and has the advantage that the attenuation can easily be adjusted to optimum ratio between the wanted signal and IM-products. I managed to built a 3-stage 136kHz filter with about 700Hz bandwidth (-3dB), but when I connected it to the big antenna it produced a lot of noise. But I am sure that with the proper ferite materials and filter component dimensions a usefull filter can be constructed. It would be great if those who already constructed good filter would let the others benefit from their experience. 73, Rik Rik Strobbe ON7YD rik.strobbe@fys.kuleuven.ac.be Villadreef 14 B-3128 Baal BELGIUM (JO20IX)