Return-Path: Received: (qmail 8529 invoked from network); 11 Nov 2003 21:26:41 -0000 Received: from unknown (HELO murphys.services.quay.plus.net) (212.159.14.225) by mailstore with SMTP; 11 Nov 2003 21:26:41 -0000 Received: (qmail 18519 invoked from network); 11 Nov 2003 21:26:32 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from post.thorcom.com (193.82.116.20) by murphys.services.quay.plus.net with SMTP; 11 Nov 2003 21:26:18 -0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1AJg1H-0004Nw-Un for rsgb_lf_group-outgoing@blacksheep.org; Tue, 11 Nov 2003 21:25:51 +0000 Received: from [194.247.47.231] (helo=mailout.zetnet.co.uk) by post.thorcom.com with esmtp (Exim 4.14) id 1AJg1H-0004Nn-FQ for rsgb_lf_group@blacksheep.org; Tue, 11 Nov 2003 21:25:51 +0000 Received: from irwell.zetnet.co.uk ([194.247.47.48] helo=zetnet.co.uk) by mailout.zetnet.co.uk with esmtp (Exim 3.36 #1 (Debian)) id 1AJg1H-0008F7-00 for ; Tue, 11 Nov 2003 21:25:51 +0000 X-Fake-Domain: johnb5a82ea1a4 Received: from johnb5a82ea1a4 (bts-0695.dialup.zetnet.co.uk [194.247.50.183]) by zetnet.co.uk (8.12.3/8.12.3/Debian-6.6.zet1) with ESMTP id hABLPmTO002501 for ; Tue, 11 Nov 2003 21:25:49 GMT X-Bad-Message-ID: no DNS (johnb5a82ea1a4) Message-ID: <003a01c3a89a$6d0fd550$b732f7c2@johnb5a82ea1a4> From: "John Rabson" To: rsgb_lf_group@blacksheep.org References: <19d.1ca91b53.2cdcf1ce@aol.com> <01ce01c3a895$53649500$ac2465d5@oemcomputer> <3FB150A2.1020407@virgin.net> Date: Tue, 11 Nov 2003 21:26:01 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Subject: Re: LF: Re: Dummy loads at LF Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.60 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 X-Spam-Rating: 2 About 30 years ago, Ongar Radio station to the north-east of London had a number of nine kilowatt HF ISB transmitters. For dummy loads they used carbon tubes about a foot long and an inch or two in diameter. Resistance was 75 ohms and they were cooled by pumping water through them. I had a box of such resistors, but they went missing in a house move. 73 John Rabson G3PAI ----- Original Message ----- From: "Stewart Bryant" To: Sent: Tuesday, November 11, 2003 9:12 PM Subject: Re: LF: Re: Dummy loads at LF > When I was a PhD student we used to make high power resistors > to terminate very large pulse generators from PVC tube filled > with copper sulphate and with brass end plugs. By varying the > size of the resistor and the concentration of the copper sulphate > we could get the value we wanted. I can't remember how powerful > these generators were (not my project), but they ranged > from the size of a small van to a very large lorry :) > > Interestingly the high frequency performance of these resistors > was not a problem. > > A quick check on Google pointed me to this design info: > > http://www.kronjaeger.com/hv/hv/comp/res/ > (It's actually interesting to also look at the top level page) > > http://www.samtech.co.uk/PDF%20files/liquid%20res.pdf > > 73 > > Stewart > > Johan Bodin wrote: > > Dear group, > > > > at a wavelength of 2200m I can't see any reason why a bucket of > > salt water can't be used as a "poor man's dummy load". Also, > > water needs a lot of energy to heat up. At 4.18 kJ/(kg*K) a 10 liter > > bucket will take a kWh, or so, before reaching the boiling point... :-) > > > > By the way, the speed (frequency) control system at SAQ contains > > servo controlled "liquid rheostats". > > > > Any ideas for electrode material? > > > > 73 > > > > Johan SM6LKM > > > > > > > > >