Patent ID: 7139581

Claim:
A method for measuring distance in a half-duplex communications loop comprising an originating transceiver and a repeating transceiver, comprising: receiving a first radio-frequency signal having a carrier frequency from among a plurality of carrier frequencies at said repeating transceiver during a reception time slot; downconverting said first radio-frequency signal to a intermediate frequency signal by demodulating said first radio-frequency signal with a local oscillator signal to produce a pair of quadrature demodulated signals at said intermediate frequency and generating a phase-lock reference signal locked to one of said pair of quadrature demodulated signals; retaining phase, frequency and amplitude information of said intermediate frequency signal within said repeating transceiver after the end of the reception time slot; upconverting said stored intermediate frequency signal to a second radio-frequency signal during a transmission time slot, said second radio-frequency signal having a carrier frequency equal to said carrier frequency of said first radio-frequency signal and a phase corresponding to said retained phase information of said first radio-frequency signal and an amplitude corresponding to said retained amplitude information of said first radio-frequency signal; and transmitting said second radio-frequency signal from said repeating transceiver during said transmission time slot, whereby said second radio-frequency signal may be received by said originating transceiver for determining a phase delay of said half-duplex communications loop.