To: rsgb_lf_group@blacksheep.org
Date: Fri, 19 Nov 1999 01:18:46 -0500
Subject: Re: LF: dummyload
Message-ID: <19991119.013350.-4889.2.riese-k3djc@juno.com>
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From: "Bob RIESE" <riese-k3djc@juno.com>
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Building the load into a container of Mineral Oil should increase the
power handling quite a bit. I suspect it would make them a continuos load
at that power level.

Bob

On Thu, 18 Nov 1999 18:17:20 Rik Strobbe <rik.strobbe@fys.kuleuven.ac.be>
writes:
>For test-puposes I needed a dummyload that could withstand 450W on 
>136kHz
>for some minutes.
>Having some 470 Ohm / 25 Watt wirewound resistors in the junkbox I put 
>9 of
>them in parallel and measured 52 Ohm with my DVM. Next I took it to my 
>work
>and checked it there on the impedance analyzer :
>at 137kHz it was 51.6 + j1.3 Ohms, so more than good enough.
>Although 9 x 25 = 225W they withstand 450W for about 2 minutes before 
>it
>starts 'smelling'. After several of these 'mistreatements' I checked 
>it
>again on the impedance analyzer and it was still 51.6 + j1.3 Ohms, so
>overheating the resistors for a shot period does not seem to affect 
>it.
>
>So, if you need a high power 50 Ohm dummyload but don't want to spend 
>too
>much money on it : just parralel a bunch of high-power wirewound 
>resistors,
>it works fine on 136kHz. For a short period (few minutes) they even
>withstand the double power they are rated for.
>
>One final remark : don't put the resistors too close together or the 
>middle
>one(s) will become too hot. I kept all resistors about 2.5cm (1 inch) 
>apart.
>
>73, Rik  ON7YD
>
>