My Smart Dummy Loads: a Shack version and a Go-Bag version!

By: Marius Lubbe ZS1ML

As a radio enthusiast, I find the Dummy Load an indispensable tool in my kit. It’s ingeniously designed to absorb radio frequency, or RF energy, without transmitting it anywhere. This comes in handy when I’m testing and tuning my radio transmitters. The Dummy Load acts as a perfect stand-in, simulating the conditions my transmitter would typically encounter when sending signals to an antenna. It’s also my go-to device when testing the power output of an amplifier or checking the SWR (Standing Wave Ratio) of an antenna system.

At its core, a Dummy Load is a resistor, specifically designed to soak up RF energy. When you would peek inside a typical Dummy Load, you will find a resistive element, like a coil or a wire-wound resistor. This element is cleverly attached to a heat sink, which serves to dissipate the heat generated by the resistive element—a heat that can be quite substantial when dealing with high power levels.

When I apply RF energy to the input of a Dummy Load, it’s absorbed by the resistive element and converted into heat. The heat sink then dissipates this heat. Since the RF energy isn’t being transmitted anywhere, it’s crucial to make sure that the Dummy Load can handle absorbing the full power output of the transmitter or amplifier I’m testing. In any case, I use the minimum power needed when using a dummy load.

Two of my favorite Dummy Loads are the MFJ-261 and MFJ-262B, manufactured by MFJ Enterprises, Inc. They’re designed to absorb RF energy, with the MFJ-261 able to handle up to 100 watts PEP (Peak Envelope Power) and the MFJ-262B capable of absorbing up to 200 watts PEP. These features make them suitable for most of my amateur radio transmitters.

The MFJ-261 is a compact and lightweight Dummy Load, making it an excellent choice for portable or field use. Despite its small size, it’s quite robust, thanks to its rugged aluminum case.

Both the MFJ-261 and MFJ-262B are traditional Dummy Loads and come with a standard SO-239 connector, making it easy for me to connect them to my transmitter.

The MFJ-262B stands out with its heavy-duty heat sink and resistive element, which can absorb up to 200 watts of RF energy. This makes it a more robust option if I’m dealing with higher power levels.

Having extensive use with both these units I can highly recommend them especially based on build quality.

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