Return-Path: Received: (qmail 28177 invoked from network); 30 Jul 2002 13:29:18 -0000 Received: from marstons.services.quay.plus.net (212.159.14.223) by mailstore with SMTP; 30 Jul 2002 13:29:18 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 18347 invoked by uid 10001); 30 Jul 2002 13:33:56 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com (193.82.116.70) by marstons.services.quay.plus.net with SMTP; 30 Jul 2002 13:33:55 -0000 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 17ZWzt-00050L-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 30 Jul 2002 14:25:09 +0100 Received: from cmailenv2.svr.pol.co.uk ([213.218.77.54]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 17ZWzt-00050G-00 for rsgb_lf_group@blacksheep.org; Tue, 30 Jul 2002 14:25:09 +0100 Received: from [62.21.151.118] (helo=w8k3f0.freeler.nl) by cmailENV2.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 17ZWzr-00047g-00 for rsgb_lf_group@blacksheep.org; Tue, 30 Jul 2002 13:25:07 +0000 Message-ID: <5.1.0.14.0.20020730150007.009e92e0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 30 Jul 2002 15:20:56 +0200 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" Subject: Re: LF: Re: Power of Donebach 153kHz TX In-reply-to: <7D653C9C42F5D411A27C00508BF8803DCB9B50@mail.dstl.gov.uk> 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

Andy, G4JNT wrote:

I've just made a check of both Droitwich and Donebach transmissions using
the WatKins Johnson WJ-8711 receiver here at work. Using the narrowest IF
bandwidth of 56Hz, setting manual gain control, and monitoring the output
tone using Gram on its widest setting I cannot detect any variation in
carrier level with modulation on either of the two transmitters. The level
meter, which indicates actual signal level, accurately calibrated in dBm,
also shows no significant variation with modulation. There is perhaps 1dB of
variation on Donebach ( due to fading ?) and nothing on Droitwich.

I'm very sure (read 99.9% certain) Droitwich has no amplitude modulation -
viewing it on a vectorscope in the past shows only the phase variation. So
perhaps you are seeing some secondary effects introduced by the receiver ?

Andy G4JNT

I repeated the reception using the Wandel & Goltermann PSM-5 selective voltmeter and a wire aerial instead of the loop. The results were identical to the SPM-12 and the loop aerial: variation in strength as read on the meter on Donebach, Droitwich and Dutch 747kHz and steady readings on other LF and MF transmitters. The variations follow the modulating signal so it is not a matter of conversion of a data PSK or FSK signal into AM.

It would be interesting to know what other amateurs find? Or provide an explanation of the anomaly?

73, Dick, PA0SE

< I am pretty sure Donebach uses some form of controlled carrier modulation,
>apart from the phase modulation mentioned by Walter.

>Our Dutch MF transmittters at 747kHz and 1008kHz are also made by
>Telefunken (400kW at daytime). The 747kHz transmitter uses controlled
>carrier to save power and expenses; the 1008kHz one does not. The carrier
>at 747kHz, as measured by the SPM-12 at 25Hz bandwidth, shows the same kind

>of fluctuations as the Donebach one, the 1008kHz carrier is steady.

>Remarkable is Droitwich at 198kHz. There the carrier goes downward during
>modulation!

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