What is the condition called when signals from two transmitters mix and create unwanted signals?

The condition in which signals from two transmitters mix and create unwanted signals is known as intermodulation interference. This phenomenon occurs when two or more signals pass through a non-linear device or medium, such as an amplifier or mixer. The non-linearity causes the signals to interact, producing additional signals at unwanted frequencies, which are typically the sum and difference of the original frequencies and their harmonics.

Intermodulation interference can lead to distortion and degraded performance in communication systems, as these unwanted signals can interfere with the desired signals, potentially causing a variety of issues, such as reduced clarity, increased noise, or complete loss of communication.

In contrast, signal distortion refers to any alteration in the signal's original shape, often caused by non-ideal components, but it does not specifically involve mixing of channels. Harmonic interference pertains to unwanted signals created by harmonics of a fundamental frequency, while frequency drift is related to changes in the frequency of a signal over time and does not involve mixing of multiple signal sources. Thus, intermodulation interference is the correct term for the scenario described.