It should be noted that different transmitters operate within the NDB band of frequencies and can be detected by the aircraft’s receiver. These include:
- Broadcast stations (i.e. those carrying entertainment, news, etc.)
- Marine Beacons.
Stations must not be used if their details are not published in the AIP or appropriate Flight Guides. Where details of Marine Beacons are published, users should note that a number of beacons are grouped together on the same frequency. Each beacon transmitting for a period of 60 seconds in a cycle of six minutes.
The use of signals from such published stations guarantees that, within the published range by day, the signal from the desired station will be at least three times stronger than any other signal on the same or near frequency. The use of transmissions from non-published sources may lead to errors, as they are not protected from such harmful interference.