John's homebrew pages

Dummy load

This really needs one or two more photos, especially of the finished coaxial resistor arrangement which is now dunked in oil.

I had never built a proper dummy load, since in the past had only had very low powers to worry about at RF; for audio some big wirewound resistors do fine. However I wanted something that will work reasonably well at 2m, so built a "coax" dummy load using 20 2 Watt 1k resistors. Here are the first four wired in to a coaxial assembly.

dummy load assembly

This also meant that, for the first time, I could measure the output of my FT-817 properly; as widely reported, it's a bit less than the advertised values. The meter in the bottom right is my trusty old Japanese meter, bought from Fradan Radio in Wigan when I was a schoolboy, at what was then to me vast cost. The box has somewhat disintegrated but the meter is still going strong.

dummy load in use

The power measurement is from the DC output produced by the rectifier sitting in a BNC plug body. The idea of the treacle tin is (a) RF shielding, and (b) it has now been filled with oil to increate the power rating of the dummy load considerably.

dummy load power assembly