Abstract: Position determining apparatus including at least one base transmitter/receiver (BTR) station including a base transmitter which periodically transmits timing signals and a plurality of mobile transmitter/receivers (MTR). Each MTR includes a mobile receiver operative to receive timing signals transmitted by at least one base transmitter; synchronization circuitry receiving the timing signals and providing a spread-spectrum frequency-hopping sequence characteristic of the particular MTR; and a mobile transmitter producing a radiated frequency hopped signal responsive to the frequency-hopping sequence and the timing signal.