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i 9Among the uses of the spectrum are: radio and television broadcasting; police, fire, ambulance, and other public-safety communications; taxicab and truck dispatching; aircraft communications; satellite links; radar; CB and ham radio communications; industrial,scientific, and medical applica- tions; and mobile and portable telecommunications. 10There are 1000 milliwatts, or 1,000,000 microwatts, in a watt. 11ERP referenced to a half-wave dipole is the cellular industry's standard way of expressing the signal power emitted from a base-station antenna. In other contexts, communications engineers sometimes speak of Effective Isotropic Radiated Power or EIRP. EIRP is the radio signal power that would escape into space from an isotropic antenna—a theoretical antenna that would radiate equally well in all directions. EIRP is not the same as ERP referenced to a half-wave dipole. A dipole is somewhat directional and, in the dipole's most favored direction, exhibits 2.1 decibels (dB) of gain (a power multiple of 1.62 times) relative to an isotropic antenna. 12The large bulb does not generate 100 watts of light. Rather, it draws 100 watts from the power source. Most of those 100 watts is wasted as heat. (A great portion of the heat radiates as invisible, infrared radiation.) Only five watts might actually radiate as visible light. 13A ten-fold power increase corresponds to a +10-dB gain, a hundred-fold increase to +20 dB, and a thousand-fold increase to +30 dB. A doubling of power is a +3-dB increase, and a quadrupling +6 dB. A two-fold drop in power is a -3-dB loss;a four-fold decrease -6 dB. A ten-fold drop in power is a -10-dB loss, and so on. 14Signal power in watts equals signal voltage in volts times signal current in amps. A 100-watt • cellular transmitter generates the same amount of power that a 100-watt bulb draws from a wall socket. In very rural areas where traffic is light and base stations few and far between, ERP can be as high as 500 watts per channel. 15Why not just increase the number of channels?Because the FCC assigns a limited amount of spectrum to each cellular carrier,and using more channels at a given base station entails more channel preclusion in adjacent service areas or"cells."Cutting ERP and antenna height while increasing the number of channels helps the network handle the localized demand without pre- venting other base stations from using the added channels. 16A Symposium participant who is a cellular communications engineer also described picocells, which have even smaller coverage areas, that cellular networks can deploy to cope with the highest- demand situations. 17Those are two major reasons why FM broadcast radio stations sound so much better than AM radio stations. 18This analog FM cellular telephone signal format is also called Advanced Mobile Phone Service or AMPS. 4110