Which of the following can cause radio frequency interference?

Radio Frequency Interference (RFI) can be caused by a variety of technical issues, making 'All these choices are correct' the right answer. Understanding these causes helps amateur operators troubleshoot and prevent interference. Fundamental overload occurs when a clean, perfectly legal signal is simply too strong for a poorly filtered nearby receiver to handle. Harmonics are unintended signals transmitted at exact multiples of your operating frequency. Finally, spurious emissions are any other unintended radio signals created by a faulty or poorly designed transmitter. Because all three phenomena can disrupt other electronics or communications, they are all valid causes of RFI.