Stupid Simple Dummy Load

- 2 mins read

This dummy load couldn’t be simpler and works great if I’m not being too stupid.

Stupid Simple Dummy Load

The resistor is a 50 Ohn 100W low inductance through-hole resistor that is good to 175C.

The heat sink is… well, it’s technically under-rated.

The heat-shrink and hot glue are definitely to spec, though.

If you do the datasheet math (as you should!) it works out that this resistor and heat sink combo is rated for about 26.5W without airflow. In my case, I’m just going to keep the power levels to 20W or less when I use the dummy load. Even if I screw up, there is some margin for error here. With a 40W continuous carrier applied for 30s, the surface temperature of the resistor package raised by just 12C, and it cools down surprisingly quickly when the power is removed. At 100W it warms by 16C in 10s, so I do have to be careful. Worst comes to worst, the package has a UL-94 flammability rating of V0 - “Superior self-extinguishing with no flaming drips”. Pretty sweet. I expect I’d smell the hot glue before I pop the resistor - hopefully I never find out.

The sweep shows that it will work pretty well across the HF frequencies

SWR on HF bands

VHF and UHF, not so much :-(

SWR on U/VHF bands

Parts list