| 摘要 |
<p>SO1263 TUNING APPARATUS Tuning apparatus is disclosed for a radio receiver having an adjustable tuning section which exhibits a tuning condition that is adjustable over a frequency range to be tuned to selected broadcast frequencies. An IF section is coupled to the tuning section to produce an IF signal as a function of the frequency to which the tuning section is tuned. An IF detector detects whether the IF signal corresponds to a signal received on a broadcast frequency to which the tuning section is tuned. If the tuning section is tuned to a broadcast frequency, a tuning indicating signal is produced. This tuning indicating signal is produced whether the received signal is a relatively high or a relatively low level signal. The IF detector also produces the tune indicating signal if the tuning section is tuned to a frequency that is within a predetermined amount of a broadcast frequency and the received signal is a relatively high level signal. An adjusting circuit changes the condition of the tuning section in predetermined frequencies selectively in an upward or downward direction. A sensor senses that the tune indicating signal has been produced so as to enable the adjusting circuit to change the tuning condition of the tuning section by a predetermined frequency step and then to disable the adjusting circuit if the tune indicating signal still is sensed following this frequency change so as to maintain the last-attained tuning condition. Alternatively, if the tune indicating signal no longer is sensed after the tuning condition has been changed by the predetermined frequency step, the tuning section is returned to its preceding tuning condition by this predetermined frequency step. Consequently, if the received signal is a high level signal, the tune indicating signal is produced when the tuning condition of the tuning section differs from a broadcast frequency by this predetermined frequency step; and the tuning condition then is changed by this step so as to arrive at the desired broadcast frequency. If, however, the received signal is a low level signal, the tune indicating signal is produced only when the tuning condition of the tuning section coincides with a desired broadcast frequency, and then this tuning condition is changed by one step followed by a return of one step to the proper condition. - ii</p> |
