Communications: electrical – Systems – Call station
Patent
1975-04-23
1976-10-19
Swann, III, Glen R.
Communications: electrical
Systems
Call station
343 5PD, G08B 1324, G08B 1322
Patent
active
039874273
ABSTRACT:
A Doppler principle detection device includes means for transmitting signals into a field to be protected, means for receiving signals from said field, quadrature mixers for multiplying a reference signal and the received signal to discern between positive and negative Doppler shifts, an integrator for integrating the output of the detection device and an alarm adapted to be activated when the output of the integrator reaches a predetermined threshold level and incorporating a false alarm inhibitor for shifting by 90.degree. the difference in phase of the received signals with respect to the reference signal. In one form the false alarm inhibitor comprises analogue switches connected to a level detector and to an inverter connected to the level detector arranged to switch phase shifted signals to the quadrature mixers to shift the phase of the reference signal by 90.degree.. In an alternative form a digital signal oscillator is connected to a divider and has its phase quadratured outputs switched by a level detector to achieve the same 90.degree. phase shift in the reference signals.
REFERENCES:
patent: 3727216 (1973-04-01), Antonio
patent: 3733581 (1973-05-01), Kalmus
patent: 3760400 (1973-09-01), Galvin et al.
patent: 3863240 (1975-01-01), Galvin
Nidac Pty. Limited
Swann III Glen R.
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