What is a Dummy Load in Amateur Radio?

What is a Dummy Load in Amateur Radio?

Dummy load is a device connected to the output of an amateur radio transmitter for testing purpose. Electrically it simulates an antenna and allows adjustment of the transmitter without sending out electromagnetic waves. It can also be called as a dummy antenna. Using a transmitter without a dummy load or antenna leads to reflection of power back to the final stages, causing overheating and damage to the circuitry.

Typically a dummy load consists of a resistor with value equivalent to the output impedance of the transmitter and the characteristic impedance of the antenna, usually 50 Ohms. As the resistor can heat up when the power is delivered, a cooling system is needed. A simple method is to immerse it in mineral oil which absorbs the heat generated. Dummy loads with other types of heat sinks are also commercially available. Dummy load provides an SWR of 1:1 to avoid power being reflected back to the transmitter. If you adjust the transmitter by connecting the antenna instead, it will cause interference on the amateur radio band.