Return-Path: Received: (qmail 14178 invoked from network); 21 May 2000 08:13:44 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by grants.core.plus.net.uk with SMTP; 21 May 2000 08:13:44 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12tQhx-0005s7-00 for rsgb_lf_group-outgoing@blacksheep.org; Sun, 21 May 2000 09:03:33 +0100 Received: from lepidachrosite.lion-access.net ([212.19.217.3]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12tQhw-0005s2-00 for rsgb_lf_group@blacksheep.org; Sun, 21 May 2000 09:03:32 +0100 Received: from w8k3f0 (2410808417.dialin.freeler.nl [143.178.4.97]) by lepidachrosite.lion-access.net (I-Lab) with SMTP id 98A97CAF17 for ; Sun, 21 May 2000 08:02:28 +0000 (GMT) Message-ID: <001c01bfc2fb$279acee0$6104b28f@w8k3f0> From: "Dick Rollema" To: "LF-Group" Subject: LF: Fw: Best tone for aural copy Date: Sun, 21 May 2000 10:03:25 +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 In an e-mail to Bob, ZL2CA. discussing the PA0LQ audio filters, I mentioned a thesis on the reading of morse code signals in noise. As a result Bob asked: > Do you know a way of accessing the university and thesis details? > I gave the following reply which I also sent to the reflector because others may be interested in it. Bob, The thesis has the title "Signal detection in noise, with special reference to telegraphy". The author is Peter Montnémery, SM7CMY, who is employed at the Department of Otorhinolaryngology [say that fast ten times :-)], Head and Neck Surgery, University Hospital, Lund, Sweden. Code number is ISRN LUMEDW/MERL -- 1038--SE. Some of the subjects treated are: 1. Recognition of telegraphy disturbed by noise at different S/N-ratios and different telegraphy speeds. 2. Recognition of telegraphy signs at different listening levels and frequencies. 3. Effect of dichotic presentation on the recognition of telegraphy signals. 4. Recognition of telegraphy in hearing-impaired telegraph operators. 5. Performance of electronic morse decoders in decoding telegraphy masked by noise. 6. Detection of trains of tone pulses masked by noise. I learned about the thesis by a message from Peter Schnoor, DF2FL, via the LF-Group reflector, considerable time ago. Via a friend at the Leyden University I managed to obtain a copy which took many months to arrive. After writing an article about it for our VERON magazine "Electron" (still waiting to appear) I have passed it on to my good friend PA0CX/F2ZI who will or already has sent it to Pat Hawker, G3VA. > As a further aside, do you know why Harry picked 1000 Hz for his filter? I don't know. For my filter I had to use 1000Hz because my German LF-receiver of the sixties has a fixed BFO that produces an audio note of 1000Hz when the signal is centred in the IF filters. But when I am busy in my shack doing other jobs I often leave the receiver on with a wide IF-filter selected, no audiofilter and such high volume that the headphones function as speaker. I have noted several times that I could detect a weak signal this way. After putting on the headphones and switching on the 30Hz audio filter it was often very difficult to read the signal! It again goes to show that the ear-brain combination acts as tracking bandpass filter that should not be "assisted" by too much pre-filtering. 73, Dick, PA0SE