| 摘要 |
A communications system including: a plurality of sub-surface portable transceivers each including: a digital data source, a modulator coupled to the digital data source, a power amplifier coupled to the modulator and a loop antenna inductively coupled to the power amplifier; and a base transceiver including: an electrically insulated ferrite core antenna for receiving magnetic signals, an electric di-pole antenna for receiving ambient noise, a noise canceller coupled to the insulated ferrite core antenna and electric dipole antenna and responsive to the electric-dipole antenna to filter noise from signals received via the insulated ferrite core antenna, a demodulator coupled to the noise canceller and a decoder coupled to the demodulator.
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