It’s all well and good building stuff but if you can’t test it’s functioning you’re on a hiding to nothing.
With that in mind I wanted to obtain/build a dummy load for testing my embryonic QRP builds.
After a bit of Google time I found a YouTube post by Tony Milluzzi, KD8RTT which was nice and simple. There were all sorts of kits and other homebrew suggestions out there but for simplicity this wins hands down.
eBay provided a 50 ohm 1% thick film resistor in a TO-220 package along with a big heatsink.
On testing the resistor on a multimeter the resistance was 50.1 ohm. Not complaining at that!
The next trick was some sort of case. I was loathed to spend any more than was necessary on this and boxing something up that was going to get warm or hot didn’t seem an altogether good idea.
As such I wanted an open design to allow maximum heat dissipation from the heatsink.
I hit on the idea of cannibalising an old metal case from a D-Link switch that went bang several weeks ago and was lurking in the top of the bin still.
It was at this point I discovered that 2mm steel really won’t cut with a hack saw and resorted to gentle application of an angle grinder fitted with a metal cutting disk. That said, after about 5 minutes work …
The swarf was razor sharp and a reasonable amount of time was spent with a file and some wet & dry paper removing potential health problems!
Getting a hole through it to mount the SO-239 chassis mount socket was a bit tricky but we got there.
A liberal application of thermal conductive paste between the resistor and the heatsink is a no brainer to ensure maximum dissipation, then a quick solder job to finish things off.
If I’m feeling precious I may spray it all the same colour with a rattle can if I ever get bored, but for an hour’s work and minimal expenditure I’m not complaining!
One by 50 ohm 1 Watt QRP dummy load, done!