Aeronautical NDB's

Common types of Aeronautical NDB's antennas are:

A) Flattop wire array consisting of one up to three parallel horizontal wires a few feet apart.
B) Loaded Marconi vertical antenna.
Despite the use of different technics to artificial increase the electrical length of the above antennas the physical length relative to the wave length remains too short and for resonance ( when an antenna is resonant its capacitive reactance equals its inductive reactance and the antenna acts as a pure resistance) a suitable matching network is required.
For both type of antennas a very good ground plane is needed in order to improve the radiating efficiency .

Aeronautical and marine NDBs as well, are popular among the DX'ers because NDB signals normally can't be heard over long distances, but favorable conditions in the ionospher can allow those signals to travel much farther than normal and when it happens it becomes very interest for the DX'ers.

Here is a list of Aerinautical NDB's in Greece, for DXers