An automatic broadcast wave tuning device for RDS receiver

Claim 1

An automatic broadcast wave tuning device for a radio data system (RDS) receiver comprising: a front end unit (2) for receiving a RDS broadcast wave carrying a list of alternative frequencies data (AF) and a program identification code (PI) of a group of broadcasting stations, which belong to the same broadcasting network, by tuning in a broadcasting station within the same broadcasting network; a phase-locked loop (PLL) circuit (6) for performing the tune-in operation of the front end unit (2) by varying a frequency dividing ratio thereof; a frequency discriminator (3) for discriminating a frequency modulated (FM) signal output of the front end unit (2); a multiplex demodulator circuit (5) for outputting an audio signal by demodulating a discriminated output of the frequency discriminator (3); a level detector (7) for detecting a received signal level by accepting the discriminated output of the frequency discriminator (3); a RDS decoder (9) for decoding the discriminated output of the frequency discriminator (3) into prescribed readable data; an alternative frequencies (AF) data memory (11) for storing the program identification code (PI) carried by the broadcast wave presently tuned in; and a controller (10) connected to the phase-locked loop (PLL) circuit (6), the level detector (7) and the RDS decoder (9) for controlling the frequency dividing ratio of the phase-locked loop (PLL) circuit (6) by receiving a detected output of the level detector (7) and a decoded output of the RDS decoder (9), characterized in that control is performed such that it is determined whether or not the program identification code (PI) of an alternative station is readable based on the detected output of the level detector (7), when it is determined that the program identification code (PI) is unreadable but a received signal level of the broadcast wave of the broadcasting station within the same broadcasting network is at or above a predetermined signal level, the frequency dividing ratio of the phase-locked loop (PLL) circuit (6) is so controlled as to tune in the former broadcast wave and a forbidden flag is set to the corresponding frequency of the alternative station for forbidding the next tune-in to that station, whereas when it is determined that the program identification code (PI) is readable but the readable program identification code (PI) is not identical with that of the broadcast wave presently tuned in, the frequency dividing ratio of the phase-locked loop (PLL) circuit (6) is so controlled, without discriminating a level of the received signal from the detected output of the level detector (7), as to return to tune in the former broadcast wave and a forbidden flag is set to the frequency of the alternative station to prevent switching to that station carrying the forbidden flat in the next switching operation within the same broadcasting network.