Abstract: An electrostatic tag formed from an antenna and a capacitor is disclosed. The capacitor has a charge which changes from a first charge value to a second charge value when the voltage across the capacitor reaches a first threshold value and from the second charge value to the first charge value when the voltage reaches a second threshold value. The capacitor has a dielectric which changes from a first to second dielectric value and from the second to first dielectric value at the first and second voltage thresholds. The capacitor plates also are extended beyond the dielectric to form the antenna of the tag. The tag is used in an electronic article surveillance system which generates an electrostatic field which causes one or the other of the threshold voltages to be exceeded when a tag is exposed to the field. This results in a charge change in the capacitor and a detectable electrostatic pulse is generated.

Abstract: A magnetic article surveillance system utilizing microcomputer control and unique time domain and frequency domain information gathering channels whose information is processed by the microcomputer via preselected time domain and frequency domain criteria.

Abstract: A mobile vehicular repeater detects the termination of a received transmission from a portable transceiver to be repeated and, in response to such detection, activates the up-link radio transmitter so as to send an acknowledgement signal to the message originating portable transceiver station signifying the probable successful conclusion of a repeating operation. Special techniques are utilized to prevent confusion between such an acknowledgement signal and similar prioritizing transmissions on the up-link frequency.

Abstract: Binary messages received over a radio channel are subject to fading or noise degradation because of the radio channel. Accordingly, a predetermined binary preamble followed by a synchronizing word are transmitted ahead of the message. In order that the synchronization be correct, the end of the preamble should be determined as accurately as possible. This is achieved by fast and slow detectors which receive the preamble. The fast detector output is applied to a time delay. The slow detector and the time delay outputs are applied to an output circuit which produces an output signal in response to the slow detector and the time delay outputs both being present. The fast and slow detectors and the time delay are arranged so that the output signal is produced at the desired time after the preamble begins, thereby accurately indicating when the synchronizing word is to begin.

Abstract: In radio communication systems transmitting voice and data, data is frequently transmitted at the beginning of the transmission, and this may then be followed by voice. The sound of the data in the receiver loudspeaker is unnecessary and often annoying. This sound is eliminated by a muting circuit which initially mutes the receiver for a predetermined time following receipt of a carrier signal, and then mutes the receiver when data is detected. After the data ends, the receiver is unmuted if a carrier is still present.

Abstract: A plurality of transmitters, such as radio transmitters, frequently share a common communication medium or path, such as a single radio frequency channel. In order to prevent two transmitters from simultaneously transmitting over the common medium, each transmitter is provided with control apparatus. This apparatus causes transmission in response to a start action and in the absence of any other transmission on the medium. The apparatus also produces a repeating signal at predetermined intervals in response to the start action, so that if there is a transmission on the medium, the repeating signal continues until such time as there is an absence of any transmission on the medium. The repeating signal then causes a transmission, and thereafter the repeating signal is stopped. The interval between repeating signals may be the same for each transmitter, but simultaneous transmission by two transmitters will not or is very unlikely to occur because start times are likely to be different.