Low Frequency Telemetry from Terradynamic Vehicles

Abstract

A telemetry system has been designed and built which transmits digital data from a buried earth-penetrating vehicle to the surface by magnetic induction. The transmitting package is a cylinder 10 cm in diameter by 30 cm long and draws 5 watts of dc power while transmitting. Error rates of 1.16 x 10⁻⁴ have been obtained at a range of 52 meters through soil at a data rate of 50 bits/second, utilizing only the 0-50 Hz region of the electromagnetic spectrum. Projected performance of the system in high-conductivity media indicates useful ranges exceeding 50 meters in media as conductive as sea water (4 mho/meter). System improvements are discussed which should allow severalfold increases in data rate or range over the experimentally obtained values.