I needed a slightly more powerful dummy load than the one I built previously (you can check it out here: https://techestigate.com/250w-rf-dummy-load/). This project focuses on building a high-power 50 Ohm RF dummy load. As usual, I tried to reuse as many parts as I already had on hand, although I still needed to purchase non-inductive resistors. I picked up four 50 ฮฉ, 250 W resistors on eBay for a total of $23. By connecting two in series and then paralleling the two series pairs, I ended up with a 50 ฮฉ load once againโbut this time with significantly increased power handling.
Building concerns
I did have some concerns about using wires to interconnect the resistors, as this can introduce unwanted effects at higher frequencies. However, since my current needs are limited to the HF bands, I expect this design to perform just fine. Thermal management was a key consideration. To dissipate as much heat as possible, I sandwiched the resistors between two heatsinks. One challenge I paid close attention to was the proximity of the resistor terminals to the upper heatsink. To avoid any risk of arcingโsomething Iโve had unpleasant experiences with in the pastโI machined aluminum spacers to maintain safe clearance. You can see these spacers in the photo below.
On the bright side, this time I managed to complete all the drilling and tapping without breaking a single bit or tapโa small but satisfying victory. Aluminum can be surprisingly tricky to work with, especially when milling.
Ready for active cooling
Overall, Iโm quite happy with how this build turned out. Itโs another useful addition to my workbench, and it was genuinely enjoyable to put together. Of course, if I plan to run it at several hundred watts continuously, active cooling will be necessary. Iโve already prepared a set of blowers salvaged from an HPE server, which should do an excellent job.
I hope you like this build. Itโs not perfect, but it does exactly what I need it to do.
Hope to hear you on the band.
E70BS