| 摘要 |
An AM radio receiver includes search tuning such as seek or scan tuning features whose stop thresholds for locking onto a received frequency are adapted to environmental conditions. In the preferred embodiment, wideband signal strength, preferably derived from the automatic gain control of the radio frequency amplifier, provides a representative signal to the microprocessor for adapting the thresholds used during search tuning. The thresholds are increased when significant energy is present in the AM band and proportioned to the level of that energy. The decision logic of the microprocessor adapts thresholds according to the tuned signal strength, to wideband signal strength, to nighttime operation during which ionosphere conditions increase transmissibility of distant radio signals, and to intermediate frequency (IF) count validity to reduce the probability of stopping on audibly noisy frequencies when the RF signal environment is noisy.
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