Definition
A transformer in which the primary and secondary windings are wound side by side from two wires laid parallel along the core, producing extremely tight magnetic coupling between them. This construction gives the transformer a very flat frequency response and is used where signal fidelity across a wide band is important.
Plain English
A transformer where two wires are wound together at the same time, side by side, so the two coils are physically as close as possible. That tight pairing makes the transformer pass signals very faithfully across a wide range of frequencies.
Context Anchor
Seen in aircraft electrical, radio, ignition, and instrument-system component descriptions, usually in maintenance or technical reference material rather than normal cockpit use.
Derivation
From Latin 'bi-' meaning two, and 'filum' meaning thread or wire. So 'bifilar' literally means 'two-wire' -- describing the construction method where two wires are wound together as a pair.
Why Pilots Care
A pilot usually does not operate a bifiliar transformer directly, but recognizing the term helps when reading about electrical components that affect ignition, communication, or instrument operation.
Analogy
Think of two garden hoses wrapped together around the same reel. They stay separate, but because they follow the same path, anything about the winding shape is shared closely by both.
Intuition Check
Do not read “bifiliar transformer” as two transformers. It means one transformer with two wire coils wound together side by side.
Example Sentence 1
The technician replaced a bifilar transformer in the radio's signal stage after isolating the fault to that component.
Example Sentence 2
The radio installation used a bifilar transformer to maintain balanced signal transfer between the antenna and the transceiver.