Reverse Beacon Network is an internet-based network of dedicated wide band receivers around the world which decode CW signals in real time and generate “spots” which contain frequency, signal strength, and other information. The effect is that of a traditional beacon in reverse—instead of checking propagation by tuning one’s receiver to a transmitting beacon at a particular frequency, one merely transmits (usually by calling CQ on CW) while connected to an RBN to see which of the receivers on the network hears you.
An Amateur Radio Blog by DX Engineering 
