| 摘要 |
A security and surveillance system having a central monitoring station connected to a plurality of remote installations or subscribers by a transmission medium having a finite bandwidth. Each remote installation includes a plurality of surveillance equipment, including video, audio, and alarm signals, associated with a plurality of monitored locations. The security information collected by the surveillance equipment is serially sampled by a switcher which provides that information to an interface unit transmitter. The interface unit transmitter compresses the video information and decodes the alarm information and then using a key frequency and single side band modulation techniques modulates and sub-channelizes the processed security information into a frequency spectrum. The sub-channelized security information is translated in frequency and transmitted on the transmission medium. The information received at the central station is demodulated, and the alarm information monitored by means of a command computer. The system provides an upstream command channel so that the central station can communicate with each remote installation. The central station generates a master randomly varying reference frequency which is used to produce all of the unique key frequencies for each remote installation. There is also provided a back up on-site recorder and an alternative downstream transmission capability.
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