A method and system for distance measurement in a low or zero intermediate frequency half-duplex communications loop provides a mechanism for measuring the distance between two transceivers without synchronizing the local oscillators of the two transceivers. The system includes a vehicle and a secure server. The components are aligned and a compressive pressure is exerted on the aligned components. Temperature andor pressure changes may be effected in the Bragg reflector by, for example, a thermoelectric cooler andor piezo transducer.