as Kenwood, EF Johnson, and GE/Ericsson) can be found/discussed. The advent of issues involving interference to the PAVE PAWS RADAR systems located on the East and West coasts of the United States has pushed many amateur repeater operators to vacate the 70 cm band in favor of 33 cm, and proliferation of 33 cm repeaters has understandably increased exponentially in the past few years. Using repeaters Amateurs who use local repeaters on the 33 centimeter band use commercial handheld or mobile 900 MHz radios. As shown above, these radios can transmit between 896 and 902 MHz and receive between 935 and 941 MHz. Getting many of these radios to transmit on the repeater's input frequency (between 902 and 903 MHz) and receive on the repeater's output frequency (between 927 and 928 MHz) usually requires very little or no circuit modification, depending on the choice of radio. For instance, the Motorola model GTX (mobile and handheld versions) do not require any hardware modifications at all. Using these commercial radios however, has one handicap: flexibility. Unlike most other ham radio bands, in which one can tune to any frequency within an amateur band, modification of "Channelized" commercial radios maintains them in a channelized state. Therefore, once programmed, the frequencies they operate on cannot be changed at will without re-programming. However, since almost all FM radio equipment used on the 33 cm band amateur band was previously designed for and internally programmed for frequencies outside the 33 cm band edges, reprogramming is always necessary to get them working properly between 902-928 MHz after any physical modifications have been made. This includes the GTX. Linking Many amateurs have found the 33 centimeter band to be ideal for linking repeaters together. Some of the biggest linked repeater systems in the United States use the 33 centimeter band as their link backbone. Propagation characteristics Signal propagation on the 33 centimeter band is very dependent on the transmitting and receiving antenna's line of sight. Because of this, many wide-area coverage systems like repeaters are located on top of large hills and mountains which overlook a vast area. This ensures that the transmitting antenna is higher than terrestrial obstructions such as trees and buildings. Assuming that the transmitting antenna's wavelength, height above average terrain, and effective radiated power is equal, a transmitted signal on 33 centimeters will, generally speaking, usually travel about 3/4 of the distance that the