Telecommunications – Receiver or analog modulated signal frequency converter – Measuring or testing of receiver
Reexamination Certificate
1998-03-10
2001-05-08
Urban, Edward F. (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Measuring or testing of receiver
C455S001000, C455S063300, C455S067700
Reexamination Certificate
active
06229997
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to radio frequency receivers such as those used in wireless alarm systems in communication with a plurality of alarm sensors, and in particular radio frequency receivers comprising an interference detection circuit capable of detecting continuous and non-continuous interference.
Wireless security systems operating in residential and commercial buildings are often relied upon for “Safety of Life” applications where an alarm condition may signify a health or security emergency. Many national regulatory agencies place stringent requirements on the operation of these types of systems. For instance, in the United States Underwriter's Laboratory issues specifications, in the United Kingdom British Standards apply and in most of Europe CENELEC harmonized “norms” provide standardized requirements.
These specifications all include a requirement for the protection of system integrity against interference and jamming in the band of operation. Typically, it is required that an interference or trouble condition be indicated when a Continuous Wave (CW) Interferer or continuous interference source operates at a given power level (e.g., eight decibels above the sensitivity of the receiver) for a specified duration of time (e.g., for thirty seconds during a one minute duration or more than ten seconds). Likewise, an interference or trouble condition must be indicated when a non-continuous interference source, such as a stream of toggling data (e.g., 101010101010 . . . ) at the characteristic data rate of the system, persists for a specified duration of time (e.g. more than ten seconds) at a given power level (e.g., eight decibels above the sensitivity of the receiver).
Many low-cost systems are optimized for operation using Manchester encoded data to amplitude modulate (AM) wireless transmissions. At a corresponding receiver, the demodulated input is ac-coupled to block dc levels using, for instance, a capacitor in series between the antenna output and the receiver input. This is a particularly efficient method for decoding Manchester encoded data streams. However, the problem with ac-coupling is that it blocks continuous interference (which appears as a dc level upon demodulation) as well and, ideally, the system should detect the presence of continuous interferers and act accordingly. Another problem with ac-coupling is that despite the careful choice of capacitive values to match the data rate of the wireless transmission system, the resulting decay time of the ac-coupling may still be too fast or too slow to pass a particular non-continuous interference data stream.
Therefore, it would be advantageous if a communication system was suitable for use with alarm systems while providing means for effectively detecting continuous as well as non-continuous interference. In addition, such a system should provide a low cost solution to the interference detection problem that is readily adaptable to various national requirements specifying different interference parameters and patterns.
SUMMARY OF THE INVENTION
In accordance with present invention, a method for detecting interference in radio frequency signals is provided which comprises the steps of converting a dc-coupled signal into digitized information, comparing a set of characteristics of the dc-coupled signal to a set of reference characteristics, providing an interference status signal in an off state when the step of comparing indicates presence of interference in the dc-coupled signal, and providing the interference status signal in an on state when the step of comparing indicates absence of interference in the dc-coupled signal. The set of reference characteristics may comprise frequency or voltage characteristics of the interference. The method for detecting interference in radio frequency signals may further comprise the steps of increasing a charge voltage in response to a dc-coupled signal during a charging time when the dc-coupled signal comprises interference, decreasing a charge voltage in response to a dc-coupled signal during a discharging time when the dc-coupled signal comprises substantially no interference, comparing the charge voltage to a reference voltage, providing an interference status signal in an off state when the charge voltage is less than the reference voltage, and providing the interference status signal in an on state when the charge voltage is greater than or substantially equal to the reference voltage. The duration of the charging and discharging times may be modified by modifying values of circuit components. Noise may be reduced in the dc-coupled signal prior to the step of comparing the charge voltage to the reference voltage.
In further accordance with the present invention, an apparatus for detecting interference in radio frequency signals is provided which comprises means for converting a dc-coupled signal into digitized information, means for comparing a set of characteristics of the dc-coupled signal to a set of reference characteristics, means for providing an interference status signal in an off state when the means for comparing indicates presence of interference in the dc-coupled signal, and means for providing the interference status signal in an on state when the step of comparing indicates absence of interference in the dc-coupled signal. The apparatus for detecting interference in radio frequency signals may further comprise means for increasing a charge voltage in response to a dc-coupled signal during a charging time when the dc-coupled signal comprises interference, means for decreasing a charge voltage in response to a dc-coupled signal during a discharging time when the dc-coupled signal comprises substantially no interference, means for comparing the charge voltage to a reference voltage, means for providing an interference status signal in an off state when the charge voltage is less than the reference voltage, and means for providing the interference status signal in an on state when the charge voltage is greater than or substantially equal to the reference voltage. The apparatus for detecting interference in radio frequency signals may further comprise means for buffering the dc-coupled signal prior to the step of comparing the charge voltage to the reference voltage.
In still further accordance with the present invention, a circuit for detecting interference in a radio frequency signal is provided which comprises a charge monitoring device and a comparator. The charge monitoring device provides a charge voltage and increases the charge voltage in response to a dc-coupled signal during a charging time when the dc-coupled signal comprises interference. The charge monitoring device decreases the charge voltage in response to the dc-coupled signal during a discharging time when the dc-coupled signal comprises substantially no interference. The comparator compares the charge voltage to a reference voltage and provides an interference status signal in an off state in response to the charge voltage being less than the reference voltage. The comparator provides the interference status signal in an on state in response to the charge voltage being greater than or substantially equal to the reference voltage. The charge monitoring device comprises a charging path and a discharging path. The charging path may comprise the serial connection of a first resistor, a diode, a second resistor, and a capacitor between a supply voltage and ground. The duration of the charging time which results in a predetermined charge voltage is varied by modifying values of the first resistor, the second resistor, and the capacitor. The discharging path may comprise the serial connection of a third resistor, a diode, a second resistor, and a capacitor between a supply ground and ground. The duration of the discharging time which results in a predetermined charge voltage is varied by modifying values of the third resistor, the diode, the second resistor, and the capacitor. The circuit for detecting interference in radio frequency signals may further comp
Barkume Anthony R.
Greenberg & Traurig, LLP
Jackson Blane J.
Pittway Corp.
Urban Edward F.
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