NDB stands for "non directional beacon". These beacons are used for airborne and marine navigation.
They operate in the LW and MW bands. Although there use is for distances from some 10th up to some 100th
kilometers they can be received at much higher distances when propagations are well. Many SWLs and
hams have found NDB DXing as a new field of operation in their radio technique passion. The internet
is full of information on NDBs. So I do not want to repeat all that stuff again :-). Some good links on NDB
NDB Onlinelog Europe
NDB samples WAV files
Here are some WAV samples of logged NDB' from my location. Receiver is a ICOM IC-R71E with a 500 Hz
CW Filter. The antenna is a homebrew active antenna with a 1m whip (6mm aluminium tube). Nevertheless
I get also good results with my 40m attic dipole without any additional matching networks. The signals are
much lower with the dipole however there is also much lower noise and distortion from
NDB NKR The NDB NKR is just 20km
north of my location transmiting 24h, so good to use as a reference.
NDB HDL USAF Helicopter Airbase