| 摘要 |
<p>Apparatus and method for communication by use of a single FM radio frequency, from a plurality of transmitters to a central receiver in a security alarm system or similar system. A transmitter's radio frequency signal is modulated in wide frequency swings to transmit digitally encoded address, subaddress, and sensor status information in a very brief format. A transmission is provided periodically from each transmitter, but a very low duty cycle is used to avoid interference among the transmitters. A transmitter frequency sweep provides the receiver an opportunity to lock onto a transmission before data is transmitted. Thereafter the receiver automatically tracks the rapidly varying frequency of the transmitted signal. Address and subaddress data identify each transmission and a maintenance warning ir provided by the receiver-decoder unit to identify any transmitter which fails to reportwithin a predetermined time. Each significant sensor status change initiates a transmission from the related transmitter. Low duty cycle and low transmitter power requirements provide long transmitter battery life.</p> |
