EXTRATERRESTRIAL PROPAGATION

Communication of all sorts into space has become increasingly important. Amateurs confront extra- terrestrial propagation when accessing satellite repeaters or using the moon as a reflector. Special propagation problems arise from signals that travel from the Earth through the ionosphere (or a substan- tial portion of it) and back again. Tropospheric and ionospheric phenomena, so useful for terrestrial paths, are unwanted and serve only as a nuisance for space communication. A phenomenon known as Faraday rotation may change the polarization of radio waves traveling through the ionosphere, present- ing special problems to receiving weak signals. Cosmic noise also becomes an important factor when antennas are intentionally pointed into space.