Signal to noise ratio indicating circuit
US4038604A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 15, 1975 |
| Grant date | Jul 26, 1977 |
| Priority date | — |
| Expiry date | Dec 15, 1995 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B2001/1054
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A radio receiver squelch circuit responds to an IF carrier modulated by any of AM voice, AM pulse, CW, interrupted CW, or angle modulated signals. After the IF carrier is amplitude normalized it is supplied to a network for deriving a D.C. voltage having an amplitude indicative of the signal to noise level of the normalized IF. The signal to noise level indicating circuit includes a detector for deriving a waveform that is a replica of the envelope of the normalized IF. In response to the envelope amplitude being above a predetermined threshold level, indicative of the presence of a signal, a capacitor is discharged by a constant current source. In response to the envelope being below the predetermined level for an initial predetermined time, the capacitor is charged by a constant current source. In response to the envelope amplitude being below the predetermined level for in excess of the initial predetermined time, the capacitor is charged by a much smaller current. Thereby, the capacitor voltage level is indicative of the signal to noise ratio of the IF signal. The voltage across the capacitor is monitored with an amplitude comparison including amplitude hysteresis to derive a s…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.