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, 18.110, 21.150, 24.930, 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