The NCDXF, in cooperation with the IARU, constructed and operates a worldwide network of high-frequency radio beacons on 14.100, 18.110, 21.150, 24.930, and 28.200 megaHertz. These beacons help both amateur and commercial high-frequency radio users assess the current condition of the ionosphere. The entire system is designed, built and operated by volunteers at no cost except for the actual price of hardware components, shipping costs, and so on.
Three articles about the beacons have appeared in QST within the past few years and these articles are now available online at the IARU web site at . These articles have a lot of interesting details about the beacons. Most of the hardware used in the beacons is regular commercial equipment, but the controller is specially designed and is described in detail in Beacon Controller.
Stan Huntting, KW7KW, wrote, "There are at least two possible explanations for an apparently dead band: 1) propagation is poor, or 2) no one is transmitting. The NCDXF/IARU International Beacon Network addresses the second of these possibilities by insuring that reliable signals are always on the air, around the clock, from fixed locations worldwide." With three minutes of listening for the beacons, one can find out either where a particular band is open or which band has the best propagation to a particular part of the world.
In principle, one can simply listen on the beacon frequencies and copy the CW callsigns of the various beacons to figure out where the band is open, but in practice, not every ham operator can copy calls at twenty-two words per minute and some beacons may be heard at too low a signal strength to catch the call. Because the beacons transmit at known times, it is easy to know which beacon one is hearing without actually copying the CW callsign. Since...