Squelch detecting circuit with squelch start determining means
US4724545A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 7, 1986 |
| Grant date | Feb 9, 1988 |
| Priority date | — |
| Expiry date | Jul 7, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03G3/348
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
Abstract
A squelch detecting circuit comprises a narrow bandpass filter (16) for obtaining, as a filtered signal, a desired IF carrier frequency signal. The filtered signal is envelope-detected at a detector (17) and the detected signal is compared with a predetermined squelch level at a voltage comparator (21). The voltage comparator produces a first signal when the detected signal is below the squelch level and produces a second signal when the detected signal is above the squelch level. A squelch start determining circuit (22) produces a squelch alarm signal after the first signal is continued for a predetermined time period, and the squelch alarm signal is maintained until the second signal is inputted to the squelch start determining circuit (22), so that the transmitter and receiver characteristic test using the carrier frequency sweeping can be performed without any squelch alarm signal produced.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.