Return-Path: Received: (qmail 99317 invoked from network); 6 Mar 2005 01:21:33 -0000 Received: from unknown (HELO ptb-spamcore02.plus.net) (192.168.71.3) by ptb-mailstore01.plus.net with SMTP; 6 Mar 2005 01:21:33 -0000 Received: from mailnull by ptb-spamcore02.plus.net with spamcore-l-b (Exim 4.32; FreeBSD) id 1D7kV6-000APH-KU for dave@picks.force9.co.uk; Sun, 06 Mar 2005 01:24:09 +0000 Received: from [192.168.67.3] (helo=ptb-mxcore03.plus.net) by ptb-spamcore02.plus.net with esmtp (Exim 4.32; FreeBSD) id 1D7kV6-000APD-HA for dave@picks.force9.co.uk; Sun, 06 Mar 2005 01:24:08 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1D7kUW-0002UO-HD for dave@picks.force9.co.uk; Sun, 06 Mar 2005 01:23:32 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1D7kSD-0004Mf-G9 for rs_out_1@blacksheep.org; Sun, 06 Mar 2005 01:21:09 +0000 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1D7kSC-0004MW-Vg for rsgb_lf_group@blacksheep.org; Sun, 06 Mar 2005 01:21:08 +0000 Received: from imo-m28.mx.aol.com ([64.12.137.9]) by relay.thorcom.net with esmtp (Exim 4.43) id 1D7kSB-000557-Ef for rsgb_lf_group@blacksheep.org; Sun, 06 Mar 2005 01:21:08 +0000 Received: from MarkusVester@aol.com by imo-m28.mx.aol.com (mail_out_v37_r3.8.) id l.9a.21a5918c (4328) for ; Sat, 5 Mar 2005 20:20:58 -0500 (EST) From: MarkusVester@aol.com Message-ID: <9a.21a5918c.2f5bb4fa@aol.com> Date: Sat, 5 Mar 2005 20:20:58 EST To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 X-Mailer: 8.0 for Windows sub 6104 X-SPF-Result: relay.thorcom.net: domain of aol.com designates 64.12.137.9 as permitted sender X-Spam-Score: 0.7 (/) X-Spam-Report: autolearn=no,HTML_20_30=0.504,HTML_MESSAGE=0.001,NO_REAL_NAME=0.178 Subject: Re: LF: Re: Slow mode comparisons Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.7 required=5.0 tests=HTML_MESSAGE, HTML_TAG_BALANCE_HTML,NO_REAL_NAME autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Spam-Filtered: by PlusNet SpamCORE (v3.00) Content-transfer-encoding: 8bit Hi Alberto,

a good time of the night to discuss this last 0.8 dB ;-) My reasoning was that when variing the FFT bandwidth around the optimum BW, the readability for a symbol should change only very slightly - otherwise it wouldn't be an optimum in the sense of a zero gradient of merit. If the BW is made a little too large, you do get some more noise but also benefit from a fractional bit of incoherent averaging; on the other hand if it's too small you only gently start to decrease the signal more than the noise. Even at constant receive BW one gains by transmitting slower, eg. 5s instead of 3s DFCW dashes.

73
de Markus, DF6NM

In einer eMail vom 06.03.2005 01:13:58 Westeuropäische Normalzeit schreibt dibene@usa.net:

MarkusVester@aol.com wrote:

>My half-penny's worth is that the transmitted energy per symbol is 3.3
>times larger, giving exactly 5.23 dB improvement ;-) That's assuming
>that the FFT bandwidth is somewhere near the optimum (0.3 Hz and 0.1
>Hz respectively).

Markus,

you are correct, but in an ideal situation. Given that for performance
reasons the FFT works at its best when done
on a sample length which is a power of two, in Argo, when going from
QRSS3 to QRSS10 I multiply the sample length
by four, which causes a reduction of four times of the bin size. This
has the consequence that the noise energy that falls
into a single bin is 6 dB lower, hence the 6 dB gain in SNR.
There are algorithms to perform FFTs on arbitrary sizes, but they are
slower than when working with powers of two.

73 Alberto I2PHD