Some mobile units could be programmed to work on more than one GE Marc V trunked system. For example, if the SMR operator had a system in Bloomington and another covering Chicago, many radio models offered an "area" switch. This selected the transmit area priority. Different radio models had 29- to 100-channel capacity and there were limitations on the number of areas and the number of channels per area. In its default configuration, the radios function in the same way a talk-back-on-scan option works: regardless of which area was selected, the radio would join a conversation on the system where it was taking place.
