Definition 1 of 2
Definition
One of two antennas used by an Automatic Direction Finder (ADF) receiver. The loop antenna is a directional antenna that detects the direction from which a non-directional beacon (NDB) or commercial broadcast signal is arriving by sensing how the signal strength varies as the loop is rotated relative to the signal source. It works together with the sense antenna to resolve the direction unambiguously and drive the ADF bearing pointer.
Plain English
It is the part of the ADF system that figures out which direction a ground radio signal is coming from. On its own it can tell you the line the signal is on, but not whether the station is in front of or behind the aircraft, which is why a second antenna is needed alongside it.
Context Anchor
Seen in instrument flying when studying ADF equipment used to point toward ground-based radio beacons.
Derivation
Called a loop because the antenna is physically a loop of wire. A loop is directionally sensitive to radio waves: the signal it picks up changes strength depending on how the loop is oriented relative to the transmitter, and that is what lets it find direction.
Why Pilots Care
It supplies the directional information the ADF needs to display a bearing to the beacon, supporting instrument navigation when other aids are unavailable.
Intuition Check
A loop antenna is not related to the aerobatic maneuver called a loop. Here, loop describes the antenna’s shape and its role in sensing radio direction.
Example Sentence 1
The ADF uses input from the loop antenna and the sense antenna together to display a bearing to the selected NDB.
Example Sentence 2
When the loop antenna was aligned with the beacon, the ADF needle swung to show the correct bearing.