HF Beacon – 4S7B

IARU/NCDXF HF Beacon Network 

Beacon in Sri Lanka 4S7B

The Northern California DX Foundation NCDXF, in cooperation with the International Amateur Radio Union IARU, constructed and operates a worldwide network of high-frequency radio beacons on

  • 14.100 MHz
  • 18.110 MHz
  • 21.150 MHz
  • 24.930 MHz, and
  • 28.200 MHz.

These beacons help both amateur and commercial high-frequency radio users assess the current condition of the ionosphere. Altogether there are 18 Beacons throughout the world, and RSSL is hosting one of them in Sri Lanka. The callsign of beacon in Sri Lanka is 4S7B.


4S7B in Operation


The locations of the beacon could be viewed at


The beacons transmit every three minutes, day and night. A transmission consists of the callsign of the beacon in Morse code sent at 22 words per inute speed followed by four one-second dashes. The callsign and the first dash are sent at 100 Watts. The remaining dashes are sent at 10 Watts, 1 Watt and 100 milliWatts.

See the transmission schedule at

Full details of beacon project is on

UPDATE 25/03/2023

The 4S7B Beacon is now moved to a permanent location. Find out more info here.  4S7B Beacon Relocation