Return-Path: Received: (qmail 3688 invoked from network); 30 Jul 2002 14:55:35 -0000 Content-Transfer-Encoding: 8bit Received: from marstons.services.quay.plus.net (212.159.14.223) by mailstore with SMTP; 30 Jul 2002 14:55:35 -0000 Received: (qmail 18444 invoked by uid 10001); 30 Jul 2002 15:00:21 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by marstons.services.quay.plus.net with SMTP; 30 Jul 2002 15:00:21 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 17ZYKX-0005Ay-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 30 Jul 2002 15:50:33 +0100 Received: from hestia.herts.ac.uk ([147.197.200.9]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 17ZYKW-0005At-00 for rsgb_lf_group@blacksheep.org; Tue, 30 Jul 2002 15:50:32 +0100 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 17ZYKW-0000vh-00 for rsgb_lf_group@blacksheep.org; Tue, 30 Jul 2002 15:50:32 +0100 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 17ZYKV-0004kI-00 for rsgb_lf_group@blacksheep.org; Tue, 30 Jul 2002 15:50:31 +0100 Message-ID: <5.1.0.14.0.20020730151803.00b06398@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 30 Jul 2002 15:50:29 +0100 To: rsgb_lf_group@blacksheep.org From: "James Moritz" Subject: Re: LF: Re: Power of Donebach 153kHz TX In-reply-to: <5.1.0.14.0.20020730150007.009e92e0@POP3.freeler.nl> References: <7D653C9C42F5D411A27C00508BF8803DCB9B50@mail.dstl.gov.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Dear Dick, Andy, LF group, At 15:20 30/07/2002 +0200, PA0SE wrote: >It would be interesting to know what other amateurs find? Or provide an >explanation of the anomaly? I made some rough measurements of the FS of Droitwich and Donnebach over the weekend using an SPM-19 with 25Hz filter, and saw similar fluctuations in level to Dick's. All these signals have phase modulation of some sort applied to their carriers - it occurs to me if the RX bandwidth is narrower than the modulation sidebands produced by the PM, the result of filtering out some components of the PM signal will be an amplitude-varying signal - The higher the modulation index is, the greater the signal power in frequencies further from the carrier - a bit like the technique for calibrating FM deviation using a spectrum analyser, where with a mod index of 2.4 the carrier power drops to zero, in spite of the total signal power remaining constant. The filtered PM signal would then have an amplitude which generally decreased as the phase modulation index increased. Perhaps with the wider bandwidth of Andy's W-J receiver, all the sidebands are passed, and this does not occur? A simple experiment would be to use the spectrogram software to see how wide the phase modulation sidebands are. I also checked the France Inter signal on 162kHz, which did not show this effect - but I recall from playing around with my vectorscope circuit a while ago that the phase modulation on this signal is much slower, therefore narrower bandwidth than the Droitwich phase modulation. I will check up on this when I get home - assuming I can hear anything through the lightning QRN! Cheers, Jim Moritz 73 de M0BMU Cheers