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 <[email protected]>
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