Return-Path: Received: (qmail 508 invoked from network); 8 Jan 2003 13:14:31 -0000 Received: from netmail02.services.quay.plus.net (212.159.14.221) by mailstore with SMTP; 8 Jan 2003 13:14:31 -0000 Received: (qmail 558 invoked from network); 8 Jan 2003 13:14:26 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by netmail02.services.quay.plus.net with SMTP; 8 Jan 2003 13:14:26 -0000 X-SQ: A X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from majordom by post.thorcom.com with local (Exim 4.12) id 18WG1C-0000cU-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 08 Jan 2003 13:13:14 +0000 Received: from [64.12.136.163] (helo=imo-m08.mx.aol.com) by post.thorcom.com with esmtp (Exim 4.12) id 18WG1A-0000bx-00 for rsgb_lf_group@blacksheep.org; Wed, 08 Jan 2003 13:13:12 +0000 Received: from MarkusVester@aol.com by imo-m08.mx.aol.com (mail_out_v34.13.) id l.1a2.eb9fda9 (3956) for ; Wed, 8 Jan 2003 08:12:34 -0500 (EST) From: MarkusVester@aol.com Message-ID: <1a2.eb9fda9.2b4d7dc2@aol.com> Date: Wed, 8 Jan 2003 08:12:34 EST To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 X-Mailer: AOL 7.0 for Windows DE sub 10501 Subject: LF: DLF spurii reduced Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=1.9 required=6.0tests=NO_REAL_NAME,SPAM_PHRASE_00_01,USER_AGENT_AOLversion=2.43 X-Spam-Level: * X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rsgb_lf_group-outgoing@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Content-transfer-encoding: 8bit Hi group,

since the beginning of Dec. 2002, the daytime 153kHz BC emissions were again accompanied by the infamous spurious sidebands centered around 136kHz up to -57dBc, and a number of amateur stations in South Germany have reported increased noise levels in QSOs. After another telephone call, the system engineers in Donebach could apparently fix the spurious sidebands yesterday, and it has been relatively quiet since 13:27 UT.

The problem seems to be a design flaw in the 250kW AEG PANTEL transmitters, as it is present in both of their two units. It is caused by an unidentified parasitic oscillation in the 54-kHz swich-mode modulator drive circuitry. It was found empirically that chilling a certain CD4011 IC largely suppressed the sidebands, and the ad-hoc solution is opening up the modulator compartment and placing the affected circuit board on an extender board. - On the other hand, this condition is not very well reproducible, and the problem tends to reappear especially at high room temperatures in summer.

73 de Markus, DF6NM