Non directional beacons are low power radio transmitters used for propagation and direction finding. They can be found on long wave frequencies between 190kHz and 535kHz, and many HF frequencies. They continuously transmit identification using Morse code.
Below is a list of Non Directional Beacons (NDBs) I’ve heard using a Mini-Whip Active Antenna. I’ll be adding more beacons as and when I hear them.
Call sign
Location
Frequency kHz
Notes
I’m now using a Lowe HF150 receiver to listen to the long wave beacons. The radio runs from a 12 Volt power supply or internal rechargeable batteries so I can use it in the radio room or take it out with me. There’s more about the Lowe HF150 radio.
A Non-Directional Beacon (NDB) is a ground-based radio transmitter used primarily for aircraft navigation. NDBs have been in use since the early days of aviation and were once an essential part of the worldwide air navigation system.
They are particularly interesting to vintage radio enthusiasts because they operate on low and medium frequencies, often using relatively simple transmitter technology. Early NDB transmitters used thermionic valves.
Unlike a conventional broadcasting station, an NDB transmits a signal intended to help pilots determine the direction of the beacon.
1. How does an NDB work?
An NDB transmits a radio signal in all directions, generally using a vertically polarised antenna.
The aircraft carries a receiver called an Automatic Direction Finder (ADF). This equipment determines the direction from which the signal is arriving. The pilot can use the ADF indicator to fly towards the beacon, away from it, or along a specified bearing. The beacon itself does not know where the aircraft is located. It simply transmits continuously.
2. What frequencies do NDBs use?
Aeronautical NDBs commonly operate within the frequency range 190–535 kHz. This is the LF/MF region, and actual allocations and frequencies vary by country. This is below the normal medium-wave broadcast band, which in Europe starts at 531 kHz, although there is a small overlap.
Some beacons operate outside this general range. The relatively low frequencies allow signals to travel considerable distances, especially over seawater. However, range is affected by transmitter power, terrain, atmospheric conditions and interference.
NDB power levels vary considerably, from low-power locator beacons to transmitters operating at hundreds of watts or more.