Return-Path: Received: (qmail 2460 invoked from network); 2 Jan 2002 21:24:30 -0000 Received: from unknown (HELO warrior.services.quay.plus.net) (212.159.14.227) by excalibur-qfe1-smtp-plusnet.harl.plus.net with SMTP; 2 Jan 2002 21:24:30 -0000 Received: (qmail 12633 invoked from network); 2 Jan 2002 21:24:31 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior.services.quay.plus.net with SMTP; 2 Jan 2002 21:24:31 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 16Lsoz-0007Uo-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 02 Jan 2002 21:21:13 +0000 Received: from mailman.zeta.org.au ([203.26.10.16]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 16Lsox-0007Uj-00 for rsgb_lf_group@blacksheep.org; Wed, 02 Jan 2002 21:21:11 +0000 Received: from steve (ppp203.dyn154.pacific.net.au [210.23.154.203]) by mailman.zeta.org.au (8.9.3/8.8.7) with SMTP id IAA26232 for ; Thu, 3 Jan 2002 08:20:21 +1100 Message-ID: <009e01c193d4$1702e4e0$cb9a17d2@steve> From: "Steve Olney" To: rsgb_lf_group@blacksheep.org References: <194.97dafc.2963ca43@aol.com> Subject: Re: LF: Very slow DFCW Date: Thu, 3 Jan 2002 08:26:00 +1100 MIME-Version: 1.0 Content-Type: text/html; charset=windows-1252 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: Content-transfer-encoding: 8bit

G'day Wolf,

I had a look at the Spectrum Lab manual and see that when you say decimation you don't mean taking smaller records and then averaging (which I understood was decimation). Unfortunately, I still don't understand how this works.

If you start off with a 650Hz tone sampled at 11025Hz with a record size of 16384 you have a record length of 1.49 seconds (BW = 0.67Hz). Averaging or skipping samples could be done down to maybe a 2205Hz sample rate, but that would only get a record length of about 7.5Hz (BW = 0.134Hz). The only way I can see that 5.3mHz can be achieved is if you mix down the input signal to close to zero frequency (say 20Hz) and low-pass filter to eliminate aliasing. This would make the 16384 record length long enough for mHz range resolutions. Is this how it is done ?

73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
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