DL-250A Virtual Load Antenna | Perfect Virtual Antenna

In radio this device is also known as a dummy antenna or a radio frequency termination. It is a device, usually a resistor, used in place of an antenna to aid in testing a radio transmitter. It is substituted for the antenna while adjusting the transmitter, so that no radio waves are radiated ( although, as no dummy load is an ideal dummy load, some radiation will occur.), so that the transmitter does not interfere with other radio transmitters during the adjustments.[1] If a transmitter is tested without a load attached to its output terminals such as an antenna or a dummy load, the power will be reflected back into the transmitter, often overheating and damaging it. Also, if a transmitter is adjusted without a load, it will operate differently as compared with a load, and the adjustments may be incorrect.

The dummy load ordinarily should be a pure resistance; the amount of resistance should be the same as the impedance of the antenna or transmission line that is used with the transmitter (usually 50 Ω or 75 Ω).[2] The radio energy that is absorbed by the dummy load is converted to heat. A dummy load must be chosen or designed to tolerate the amount of power that can be delivered by the transmitter.[3] Typically it consists of a resistor attached to some type of heat sink to dissipate the power from the transmitter.

The ideal dummy load provides a standing wave ratio (SWR) of 1:1 at the given impedance.

-from wiki