METHOD AND CIRCUIT FOR DETECTING D/U, AND DEVICE APPLYING THEM

摘要

PROBLEM TO BE SOLVED: To provide a radio repeater and a radio transmitter, which can prevent sneak oscillation irrespectively of the presence or absence of a null symbol and whose transmission signal quality is more satisfactory. SOLUTION: A reception signal modulated by a sneak wave is inputted. A distortion waveform appearing in the frequency spectrum of an input signal is converted from a frequency area into a time area by a tracing circuit 28. A smoothing circuit 34 smoothes it and the level of a sneak wave is detected. A signal supplied to a transmitter is attenuated in accordance with the result and sneak oscillation and D/U deterioration are prevented. A logarithm circuit 30 and a DC cut circuit 32 remove the influence of a received signal input level. A multipath and sneak are identified by the inversion of the waveform. A slow start circuit is provided to prevent the deterioration of the signal when broadcast is started. The circuit is provided in a master broadcast machine to prevent the deterioration of the signal.