hey all.
Anyone make their own dummy loads?
Im looking for schematics for one rated to 300w

You need dummy load resistor 50ohm or two of 100ohm in parallel an a heatsink. These are flanged resistors and they bolt onto the heatsink. You just need to solder connector or cable, there is no schematic...


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http://www.ebay.ie/itm/Dummy-Load-Resis ... 25aa8b14b4

this lad should be sufficient then im guessing.

Yes. You just need good and big heatsink. Quality of heatsink is proportional to constant operating time. But you usually need less than a minute to see what you have on output...


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so what your saying is, a computer heatsink with a fan wont work

ill have a dig around and see if i have a aluminium one knocking about..

Couldnt it be put into mineral oil as well?

With all respect mate, from what I've read above I don't think you should be messing around with 300w transmitters!!!

the above was a joke, the other thread is not..
yeah i made an error, but im here to learn!

This with mineral oil is not that bad as using wire to connect amp to antenna connector... I think that was the post teckniqs was reffering to...


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haha yeah, well ive learnt my lesson.

You'd be better off with two 250 W, 100 Ohm flanged resistors in parallel, such as the Florida RF 31-1076-100-F.

You won't be able to afford an adequate heatsink to dissipate anywhere near 200 Watts from a single one of those 50 Ohm flanged resistors suggested, let alone 500 W as is written on the device. For the latter, you'd need a thermal resistance from junction to ambient of around 0.2°C/W, which is lower than the typical junction to case thermal resistance, let alone the rest. Dissipating 200 Watts only takes the required thermal resistance of the system up to 0.635°C/W, which is still largely unachievable at home.

You can find the Florida RF flanged resistors on eBay, here for example, for about 15 EUR each: http://www.ebay.co.uk/itm/RF-Resistor-R ... 1a02635255

Although forced cooling is effective, I would recommend against it for a dummy load, as you often require it in places where you don't have power available to drive the cooling fans.