Plain English Meaning
Working in two opposite directions at once. For an ADF antenna, it means the antenna can't tell whether the signal is coming from straight ahead or straight behind — both directions look the same to it.
Full Definition
Operating or responding equally well in two opposite directions. In the context of an ADF loop antenna, a bidirectional pattern means the antenna receives signals with equal strength from two opposite directions, producing two nulls and two peaks 180° apart rather than a single unique direction.
Context Anchor
Seen in ADF component discussions, especially when describing how an ADF antenna receives signals from a ground radio station.
Derivation
From Latin 'bi-' meaning 'two' and 'directio' meaning 'a directing or pointing.' Literally 'two-directional.' Knowing the 'bi-' part comes from 'two' helps lock in that this isn't about all directions or any direction — it's specifically about two opposite ones.
Why Pilots Care
A bidirectional loop antenna alone gives an ambiguous result — the station could be ahead or behind. That's why ADF pair the with a to resolve the ambiguity into a single . 'bidirectional' explains why ADF needs both to .