Return-Path: Received: (qmail 25116 invoked from network); 13 May 2000 09:47:42 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by grants.core.plus.net.uk with SMTP; 13 May 2000 09:47:42 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12qYHL-0007tg-00 for rsgb_lf_group-outgoing@blacksheep.org; Sat, 13 May 2000 10:32:11 +0100 Received: from lepidachrosite.lion-access.net ([212.19.217.3]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12qYHJ-0007tb-00 for rsgb_lf_group@blacksheep.org; Sat, 13 May 2000 10:32:09 +0100 Received: from w8k3f0 (2410825639.dialin.freeler.nl [143.178.71.167]) by lepidachrosite.lion-access.net (I-Lab) with SMTP id EA1C5CB204 for ; Sat, 13 May 2000 09:30:48 +0000 (GMT) Message-ID: <001c01bfbcbe$1b0fed60$a747b28f@w8k3f0> From: "Dick Rollema" To: rsgb_lf_group@blacksheep.org References: <09e401bfbc0e$5e55ab60$2301a8c0@maly.cz.gmc.net> <391C6885.A4BB64A8@bellatlantic.net> Subject: Re: LF: Optimal width for LF? Date: Sat, 13 May 2000 11:32:00 +0200 Organization: Freeler MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2314.1300 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: To All from PA0SE Narrow bandwidth filters do not have to ring provided they are of the phase-linear type (constant group delay in the passband). I use a home made passive phase-linear filter with a bandwidth of 30Hz and centre frequency of 1000Hz. It can pass up to 24 wpm without trouble (unfortunately the operator can't ...) The filter has four tuned circuits with coils in large ferrite potcores. Harry, PA0LQ, has designed a similar filter of the active type using 4 opamps. If you are interested in his design write to: H.A.A. Grimbergen, PA0LQ Lijtweg 1202 2341 HE Oegstgeest The Netherlands 73, Dick, PA0SE ----- Oorspronkelijk bericht ----- Van: Andre' Kesteloot Aan: Verzonden: vrijdag 12 mei 2000 22:24 Onderwerp: Re: LF: Optimal width for LF? > Petr Maly wrote: > > > Hello all > > I am just designing a new RX for 136 kHz band. It will have IF on 1 MHz with > > high quality x-tal filter with bandwidth 200 Hz. The main selectivity will > > by obtained on AF with passive filter with coils on pot cores. Till now I > > used similar filter with bandwidth about 50 Hz and it seems to be still too > > wide for LF. I was about to make it new with 15 Hz width. Somebody here > > mentioned 1 Hz wide filter which seems to me to be too narrow. At least, the > > filter cannot be narrower than obtainable osc stability. Can we make a > > little questionnaire here? What bandwidth do you use and what is the > > experience? > > > > 73, Petr, OK1FIG > > My own experience is that your narrow-band filters, if physical filters (i.e, > coils and capacitors, or crystals), are very liklely to ring. How about using > software filters? > 73 > Andre' N4ICK > > >