Return-Path: Received: (qmail 30280 invoked from network); 5 Apr 2003 08:02:18 -0000 Received: from netmail02.services.quay.plus.net (212.159.14.221) by mailstore with SMTP; 5 Apr 2003 08:02:18 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 27326 invoked by uid 10001); 5 Apr 2003 08:02:18 -0000 Received: from post.thorcom.com (193.82.116.70) by netmail02.services.quay.plus.net with SMTP; 5 Apr 2003 08:02:18 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.14) id 191ia8-0006LI-4s for rsgb_lf_group-outgoing@blacksheep.org; Sat, 05 Apr 2003 08:59:20 +0100 Received: from [213.218.77.53] (helo=cmailENV1.svr.pol.co.uk) by post.thorcom.com with esmtp (Exim 4.14) id 191ia3-0006L9-74 for rsgb_lf_group@blacksheep.org; Sat, 05 Apr 2003 08:59:15 +0100 Received: from [62.21.138.154] (helo=w8k3f0.freeler.nl) by cmailENV1.svr.pol.co.uk with esmtp (Exim 3.35 #1) id 191ia1-0002I5-00 for rsgb_lf_group@blacksheep.org; Sat, 05 Apr 2003 07:59:14 +0000 Message-ID: <5.1.0.14.0.20030405094933.01f693d0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Sat, 05 Apr 2003 09:50:51 +0200 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <5.1.0.14.0.20030404171825.024e4fd0@gemini.herts.ac.uk> References: <3.0.5.32.20030401044655.007f7b20@pop.vianw.pt> <001a01c2f7c3$800834a0$92e086d4@erica> <000501c2f7a3$1f8d9ea0$07d2fc3e@ian> <003101c2f7b3$1954f500$cbe8fc3e@l8p8y6> MIME-Version: 1.0 Subject: Re: LF: Loading coils and Decca 5501 screening Content-Type: text/html; charset=windows-1252 X-Spam-Status: No, hits=-21.8 required=5.0tests=EMAIL_ATTRIBUTION,HTML_10_20,HTML_MESSAGE,IN_REP_TO, REFERENCES,REPLY_WITH_QUOTESversion=2.51 X-Spam-Checker-Version: SpamAssassin 2.51 (1.174.2.5-2003-03-20-exp) 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 At 17:32 4-4-03 +0100, you wrote:

Dear Brian, LF Group,

At 04:46 01/04/2003 +0100, you wrote:

Only slightly off topic, but about two years ago now someone described
completing the screening on a Decca 5501. I have lost the posting but
I seem to remember that something "got hot". Does anyone have the posting
still?

Brian CT1DRP

I think that was G4JNT's off-line TX using circuit techniques from the Decca design. As I recall, When Andy initially put the TX in a steel case, the casing around the tank coil got very hot due to eddy current heating. The problem was overcome by placing aluminium sheeting between the coil and the steel casing.

That is correct. Andy published his design in QEX.

73, Dick, PA0SE

The other effect of putting additional shielding near the tank circuit coils might be to de-tune the coils slightly - but I think with the layout of the Decca PA, the effect of adding a cover on top as well as underneath would be minute. A more significant issue is obstructing the cooling - the Decca relies entirely on natural convection. On my unit I found that any top cover must have plenty of vent holes in order not to substantially increase the temperature rise of the heatsinks.

Cheers, Jim Moritz
73 de M0BMU