Definition
A form of unwanted electrical interference in which a signal or noise in one circuit is transferred into another circuit because the two circuits share a common impedance, typically a shared ground path or power supply lead. Current flowing through the shared impedance produces a voltage that appears in the second circuit as interference.
Plain English
When two electrical circuits share the same wire or ground path, the electrical activity in one can leak into the other and cause interference. That leakage happens through the shared piece of wiring they both use.
Context Anchor
Seen in aircraft electrical, radio, audio, and avionics system discussions, especially when describing how signal stages are connected inside equipment.
Derivation
Impedance comes from the Latin impedire, meaning 'to hinder' — it describes how a circuit resists the flow of alternating current. Coupling means 'joining together.' So impedance coupling literally means two circuits being joined together through a shared piece of resistance — which is exactly how the unwanted signal sneaks across.
Why Pilots Care
Unresolved impedance coupling can introduce noise into navigation and communication systems, degrading signal quality and increasing pilot workload.
Intuition Check
Impedance coupling does not mean two parts are physically fastened together. It means an electrical signal is being passed from one circuit stage to another through a component’s electrical effect.
Example Sentence 1
The technician traced the radio static to impedance coupling between the strobe light circuit and the comm radio's ground wire.
Example Sentence 2
Technicians added isolation transformers to break the impedance coupling between the power bus and the instrument circuits.