Mobile phones and other mobile devices require a network of base stations in order to function. The base station antennas transmit and receive RF (radio frequency) signals, or radio waves, to and from mobile phones near the base station. Without these radio waves, mobile communications. The base station antennas are usually placed on rooftops, in masts or on building walls. Antennas are sometimes also installed in shopping malls, airports,. Each base station can only serve a limited number of mobile devices at a time. As the number of mobile devices in a community grows, more base stations. The antenna output power level is typically between 10 and 100 watts for an outdoor base station. Television transmitters, by comparison, usually have a. Independent expert organizations have established exposure limits for radio waves based on many years of research. These limits include large safety margins. The.