A communications transceiver is implemented by modifying a GPS user equipment. In a data reception mode, a communications signal that has a carrier frequency outside the L-band, and that has been phase modulated by a PN code and by data encoded therein, is received from a conventional L-band GPS antenna. The signal is downconverted to the L-band input frequency of the GPS transceiver, and subjected to automatic gain control. The GPS transceiver software is modified so as to recognize and replicate the PN code, and to demodulate the data-bearing signal. In the data transmission mode, the data to be transmitted are modulated onto the selected PN code sequence. The data-modulated PN signal is converted to a non L-band transmission frequency. Normal operation of the GPS transceiver navigation functions is maintained in parallel with the communications functions.