In a differential global positioning system that includes one or more base stations and rover units, a system and method for including a radio modem transceiver in the rover units, and packaging several components, including the transceiver and a radio antenna in a single package, and possibly including re-chargeable batteries, a GPS receiver, and a GPS antenna in the package, to reduce the number of external electrical connections. Several of the components may be packaged into a survey range pole. GPS satellite correction information is transmitted from a base station in response to a request transmitted from the rover unit by means of the radio modem transceiver. Automatic channel selection is performed by the base stations to select a channel having low communication traffic. The rover units scan the available channels for valid GPS correction information and, in the event that more than one such channel is located, select the channel with the strongest signal.