Two out-of-band signals mixing to generate an in-band spurious signal
In-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
Two digital signals combining from alternate time slots
Local oscillator phase noise mixing with adjacent strong signals to create interference to desired signals✓Correct answer
Explanation
Reciprocal mixing is the translation of the local oscillator's phase noise into the IF passband by a strong nearby signal, which raises the apparent noise floor whenever that signal is present. The cause is the oscillator's own spectral impurity, not two out-of-band signals combining or phase cancellation in a mixer.