Abstract: A system for minimizing the effect of null zones in an interrogation zone of a marker detection system. The system includes a reference antenna system configured to produce a first reference electromagnetic field during a first time period. The antenna system also includes a phase canceling antenna system configured to produce a second electromagnetic field substantially in phase with the reference electromagnetic field during the first time period and a third electromagnetic field substantially out of phase with the reference electromagnetic field during the first time period. The phasing of the first field or the second and third fields may be continuously switched while the phase of the other is held constant. A method of spatially shifting null zones in an interrogation zone of a marker detection system is also provided.

Abstract: An apparatus for synchronized operation of a plurality of EAS systems. The system includes two or more EAS systems. Each EAS system has a receiver for receiving the same RF synchronization signal sent from a remote source, a transmitter for transmitting a marker exciter pulse and an exciter pulse receiver. The transmitter and exciter pulse receiver of each of the EAS systems are selectively enabled a predetermined time after receiving the RF synchronization signal so that all EAS systems in a localized area can be synchronized with one another.

Abstract: An electronic article surveillance (EAS) system includes a pulsed EAS transmitter, a linear power amplifier having active devices for linear amplification of signals input thereto and a controller for energizing the linear power amplifier active devices correspondingly with transmitter pulsations. A transmitter for use in electronic article surveillance, comprises a transmitting antenna, a source providing a succession of mutually spaced bursts of high-frequency signals, a linear power amplifier having active devices for linear amplification of the succession of mutually spaced bursts of high-frequency signals and a controller for selectively energizing the linear power amplifier active devices. The controller maintains the linear power amplifier active devices unenergized between successive of the mutually spaced bursts of high-frequency signals.

Abstract: An EAS central station has a number of input/output ports each for interfacing with a different personality local station. Hardware equipment and software programming of the central station have parts associated with the different personality local stations and a central processing unit selects the part of the hardware equipment and software programming associated with a local station.

Abstract: An electronic article surveillance (EAS) system includes a transmitting antenna, a driver operable for exciting the transmitting antenna, a receiving antenna and circuitry connected to the receiving antenna for improving the quality of transmissions from the transmitting antenna. The driver excites the transmitting antenna at a preselected system operating frequency and the circuitry connected to the receiving antenna improves the quality of transmissions from the transmitting antenna by lessening harmonics of the operating frequency in the transmissions. The harmonics are attributable to protection diodes connected to the receiving antenna for limiting voltages impressed thereon and otherwise adversely impacting on the receiver tag signal processing circuitry. The harmonic lessening circuitry is connected in parallel with the protection diodes and is operative to lessen protection diode harmonic generation.