Radio frequency alarm system including transmitting, coding and decoding circuitry
US4109239A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Sep 30, 1975 |
| Grant date | Aug 22, 1978 |
| Priority date | — |
| Expiry date | Sep 30, 1995 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B25/10
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
At least one component of a transmitted RF alarm signal is repetitively shifted in frequency between at least first and second frequencies chosen from among a plurality of predetermined frequencies with such shifts in frequency occurring at a predetermined switching rate. A remotely located alarm receiver detects the presence of the predetermined first and second frequencies as well as the presence of the predetermined switching rate therebetween before producing a corresponding alarm output only if both of the predetermined frequencies and the predetermined switching rate therebetween are all concurrently present. Special transmitting circuitry including encoding modulator circuitry is provided. Special decoding circuitry for incorporation at the remotely located receiver of such a system is also provided. The exemplary embodiment of such decoding circuitry incorporates a unique frequency detection circuitry which greatly increases the flexibility and reliability of the overall system.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.