The international news broadcasters:
By bouncing short-wave signals on and off the ionosphere, radio programmes can theoretically be transmitted to any point on the globe. Medium Wave AM signals have a short day-time reach, but can cover far greater distances at night when waves are reflected back to earth from the lower ionosphere. Reception at a distance, however, is not always guaranteed; atmospheric disturbances, sunspot cycles and other such factors affect dispersion of radio waves. Overcrowding of the spectrum is also a growing problem. As the number of transmissions has increased, interference has become the rule rather than the exception. Attempts to regulate, via international agreement, the plethora of short-wave broadcasters have met with some formal but little practical success. The general rule has been that the broadcaster with the strongest signal gets through, thus leading to a general increase in the number of high power transmitters and, therefore, even more interference. Both hours of broadcasting and numbers of broadcasters have increased steadily.