Communications: electrical – Condition responsive indicating system – With particular coupling link
Reexamination Certificate
1999-02-25
2001-03-13
Crosland, Donnie L. (Department: 2632)
Communications: electrical
Condition responsive indicating system
With particular coupling link
C340S506000, C340S514000
Reexamination Certificate
active
06201472
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to alarm systems having multiple remote devices in communications with a receiver/control unit wherein the receiver/control unit comprises one or more antennas; and in particular to such alarm systems wherein the receiver sensitivity is modified to increase the dynamic range of the receiver.
Contemporary radio frequency (RF) wireless security systems, such as those utilizing the ADEMCO 4281 or 5881 receiver, often use receiver antenna diversity for improving reception by counteracting the negative effects of multipath signal fading. The information transmitted from remote devices, which typically describes the state of various sensors, such as smoke, motion, breaking glass, shock and vibration detectors; door, window and floor mat switches; etc, comes from many different locations. In order to receive signals from transmitters at the maximum range, signals from transmitters at close proximity often saturate the receiver.
It is therefore an object of the present invention to provide a low cost method and system for increasing the dynamic range of a fixed gain receiver/control unit.
SUMMARY OF THE INVENTION
In accordance with these and other objects, the present invention is a method for increasing the dynamic range of the receiver/control unit of an alarm system. The alarm system comprises a receiver/control unit having a receiver associated therewith, the receiver comprising at least one antenna means and means for switching the antenna means. The control unit, or processing means, comprises signal detection means and means for controlling the antenna switching means. The method comprises the steps of selecting an input to the receiver, wherein the input maybe an output of one or more antenna means or no antenna means, and detecting the presence of a signal. The signal, likely generated by a remote transmitting device such as an alarm sensor, consists of a single or double pentad, which is one or two groups of five identical messages. Each message contains a preamble, serial number, status, etc. The control unit detects the signal by searching for the message preamble, which is the same for all valid transmissions. When a signal is detected, the selected input to the receiver stays the same until the signal has stopped being transmitted. When a signal is not detected the control unit selects a different input to the receiver. The control unit continuously switches the receiver input from one antenna, to the next antenna, to no antenna until it detects a message preamble.
The basis of the present invention is the selection of no antenna, which causes the receiver to be approximately 12 dB less sensitive. This allows the receiver to detect signals from remote transmitting devices located nearby without saturating the receiver.
The switching of the antenna means is preferably accomplished by processor control of switching diodes. In addition, capacitors may be used for better control of the residual capacitance of the switching diodes in their off state, thereby controlling the conduction of the RF input signal. The alarm system may further comprise a digital-to-analog converter for additional control of the conduction of the RF input signal.
In addition, the method may further comprise the selection of two or more antenna means, causing the receiving means to be approximately 3 dB less sensitive. In this embodiment, the connection of both antennas causes a double termination. The incoming radiated energy is the same, but the input impedance is reduced by the double termination, thereby causing the amplitude of the RF signal into the input amplifier and filters to be lower.
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Addy Kenneth L.
Linford Karl
Barkume Anthony R.
Crosland Donnie L.
Greenberg & Traurig, LLP
Pittway Corp.
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