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Decoding DME aircraft radio navigation system with the LimeSDR
(distance measuring equipment) is an aircraft radio navigation system that is used to measure the distance between an aircraft and a DME station on ground. DME is often colocated with a VOR station, in which case the VOR provides the bearing information.
This recording location also gives good geometry for TDOA (time difference of arrival) analysis for aircraft travelling along the path shown above. Due to the low duty cycle of the pulses (specially for the air-to-ground channel), the peak hold is often better than the average to detect the DME signal. To transmit a Morse dash or dot, the transponder stops listening to aircraft transmissions and replaces the squitter by a train of 1350 equally spaced pulse pairs per second.
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