SINCGARS uses 25 kHz channels in the VHF FM band, from 30 to 87.975 MHz. It has single-frequency and frequency hopping modes. The frequency-hopping mode hops 111 times a second. The SINCGARS family has mostly replaced the Vietnam-war-era synthesized single frequency radios (AN/PRC-77 and AN/VRC-12), although it can work with them. An aircraft AN/ARC-201 SINCGARS radio is phasing out the older tactical air-to-ground radios (AN/ARC-114 and AN/ARC-131). In 1992, the U.S. Air Force awarded a contract to replace the AN/ARC-188 for communications between Air Force aircraft and Army units.