A receiving device in a trunked radio communications system determines a transmit frequency, wherein the transmit frequency is calculated by subtracting a voice channel number from 559, multiplying by a channel spacing and adding a base frequency to yield the transmit frequency, if the voice channel number is between 559 and 320. The receiving device determines a receive frequency by 851.0250 MHz+[(559-a voice channel number)*12,500 Hz], if the voice channel number is between 559 and 320. In any case, the voice channel number is communicated in an outbound signaling message defined by Motorola's 3600-baud radio trunking protocol.