Apparatus and method for detecting the onset of a frequency shift keyed signal
US4423519A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 20, 1982 |
| Grant date | Dec 27, 1983 |
| Priority date | — |
| Expiry date | Jan 20, 2002 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L1/206
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
An incoming signal is tested for the presence or onset of a frequency shift keyed (FSK) signal which alternates at a known rate between two unknown frequencies separated by a known frequency shift. The incoming signal is time delayed an odd multiple of the keying period and the delayed signal is multiplied by the incoming signal to produce sum and difference frequencies when the FSK signal is present. The difference frequency is selected by filtration, demodulated and integrated to produce a useable detector signal. The detector signal is compared with a threshold signal which is generated to discriminate between the FSK signal and other unwanted signals or noise in the communication channel.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.