Return-Path: Received: (qmail 24997 invoked from network); 31 Jul 2002 11:40:38 -0000 Received: from warrior.services.quay.plus.net (212.159.14.227) by mailstore with SMTP; 31 Jul 2002 11:40:38 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 26364 invoked from network); 31 Jul 2002 11:40:40 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com (193.82.116.70) by warrior.services.quay.plus.net with SMTP; 31 Jul 2002 11:40:40 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 17ZtXC-00023X-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 31 Jul 2002 14:29:02 +0100 Received: from cmailenv3.svr.pol.co.uk ([213.218.77.55]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 17ZtXB-00023S-00 for rsgb_lf_group@blacksheep.org; Wed, 31 Jul 2002 14:29:01 +0100 Received: from [62.21.148.22] (helo=w8k3f0.freeler.nl) by cmailENV3.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 17ZrnJ-0002pR-00 for rsgb_lf_group@blacksheep.org; Wed, 31 Jul 2002 11:37:33 +0000 Message-ID: <5.1.0.14.0.20020731131032.009f66e0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Wed, 31 Jul 2002 13:41:34 +0200 To: "LF-Group" From: "Dick Rollema" Subject: LF: Transmissions from Donebach etc. MIME-Version: 1.0 Content-Type: text/html; charset=windows-1252 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Content-transfer-encoding: 8bit To All from PA0SE,

Many thanks to Andrew Talbot, James Moritz, Dave Brown, Alan Melia, Dave Pick, Markus Vester, Steve Dove and Ray Soifer for their reactions on my field strength measurement of Donebach and Droitwich.
I am happy that my findings have been confirmed by others.
As to the "downward modulation" of Droitwich: I found the same effect on the BBC World Service at about 648kHz.
The increase  of the carrier during brief moments of silence can be easily seen, not only on a selective voltmeter, but also on an oscilloscope that displays the signal. I checked that with the scope connected to the  30kHz IF of the W & G PSM-5 and also the 455kHz IF of my  pre-war HRO (with 2.5V heater valves!).

But you don't need sophisticated equipment at all. A receiver with an S-meter also shows the downward fluctuations on the BBC transmitters and the upward ones on Donebach,  Dutch 747kHz and several other stations on MF.

I don't think the phase modulation of some of the transmitters plays a role; when you listen to the transmission it is easily observed that the fluctuations follow the amplitude of the modulating signal.

73, Dick, PA0SE