Electromagnetic (microwaves) EDM instrument transmit high-frequency microwave. The measurement involves two interchangeable instruments, one being set up on each end of the line to be measured. The sending instrument transmits a series of microwaves which run through the circuitry of the receiving unit and are retransmitted to the original sending unit, which measures the phase difference between the transmitted and received signal. The net phase difference gets converted to linear distance.

In this case the inter visibility between stations is not required; however, an unobstructed measured path between stations is necessary.

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