Importance

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Abstract

A magnetic-field, noise-cancelling transceiver is provided by a dual-coil antenna circuit. In the receive mode, two identical coils, connected in series opposition, cancel noise signals common to both coils and receive desired signals present at only one coil. Capacitance in parallel with the series-opposed coils establishes the resonant frequency of the receiver, antenna circuit. In the transmit mode, the two coils, connected in series opposition, have their non-adjacent terminals clamped to ground via two pairs of oppositely-poled diodes, one pair on each non-adjacent terminal. The transmitter signal, coupled to the junction of the two coils through a capacitor, generates additive magnetic fields by causing equal currents to flow in each coil from the common junction, to their respective diode junctions, to ground through the respective, oppositely-poled diode pairs. Series resonance is established by the transmitter coupling capacitance and the parallel combination of the two coils. The transmitter and receiver tuning are independent. The receiver tuning is unaffected by the transmitter circuitry and coupling capacitance because the transmitter is connected to the null between the receiving antenna coils. The transmitter tuning is unaffected by the receiver circuitry and receiver capacitance because the diode pairs provide a relative short across the receiver input during transmission.

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First Claim