How can on-the-air interference be minimized during lengthy transmitter testing?

A dummy load is a 50-ohm shielded resistor that connects to your transmitter in place of an antenna. It dissipates the transmitter's RF power as heat instead of radiating it into the air as electromagnetic waves. Using a dummy load is the only way to perform lengthy testing without broadcasting a signal. While choosing an supposedly unoccupied frequency might seem polite, your signal could still propagate long distances and interfere with stations you cannot hear locally. Using any type of actual antenna, whether resonant or not, will radiate your test signals.