Communications: electrical – Systems – Call station
Patent
1975-09-12
1977-12-20
Swann, III, Glen R.
Communications: electrical
Systems
Call station
340276, 340409, G08B 1324
Patent
active
040644995
ABSTRACT:
A quasi-stationary electric field is produced by means of an oscillator whose output is connected to a field wire which is positioned within the area to be protected and the electric field is detected by an antenna whose output is connected to an amplifier. An AM detector is connected to the output of the amplifier and the output of the AM detector is connected via a lowpass filter to a high gain amplifying means including a bandpass filter arrangement so that at the output of this high gain amplifier only signals within the relatively low frequency range associated with movement of an intruder are present. The output signal from the high gain amplifier is fed to a threshold circuit which produces an output signal whenever the input signal thereto exceeds a predetermined threshold value, and this output signal is fed to an alarm producing circuit. The frequency of the electric field is in the range from about 1 to 40KHz and is approximately midway between two successive harmonics of the frequency of the a.c. power existing in the vicinity of the area to be protected in order to decrease the possibility of false alarms. Additionally other techniques for reducing the possibility of false alarms and for extending the utility of such a system are disclosed.
REFERENCES:
patent: 2922147 (1960-01-01), Bredesen
patent: 2956269 (1960-10-01), Schmidt
patent: 3047849 (1962-07-01), Hansen
patent: 3135951 (1964-06-01), Byrne
patent: 3237105 (1966-02-01), Kalmus
patent: 3778807 (1973-12-01), Ralston
Geiszler Theodore D.
Mongeon Ronald W.
Stellar Systems, Inc.
Swann III Glen R.
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