Detection device for presence of a digitally modulated carrier

摘要

The device includes reception of incoming signals by an antenna. The received signals are then amplified and downconverted to an IF. The signals are then passed to a pass-band filter (31) to filter adjacent channels. The output is fed to a non-linear circuit (32) such as an amplifier in saturation, which extracts the synchronous carrier frequency from the modulated signal. The synchronous frequency is then passed through a narrow band filter (33) to remove other signals to provide a filtered signal (SF) to a detector (34). The detector level (SD) is compared (35) with a reference level (REF) to determine the presence or absence of the signal, and an alarm signal is sent if no carrier signal is present. The alarm signal operates a temporary clock synchroniser to replace the carrier clock synchronisation.