| 摘要 |
Radio receivers for receiving ATSC DTV signals or NTSC analog TV signals each use a single first detector for both types of signal that supplies its output signals to an intermediate-frequency amplifier chain for DTV signals and to another intermediate-frequency amplifier chain for analog TV signals. In some receivers the sound carrier of the NTSC signal has a separate, further IF amplifier chain. When DTV signals are determined to be received, or alternatively when analog TV signals are determined not to be received, the first detector is conditioned for automatic fine tuning in response to the pilot carrier of received DTV signal. When DTV signals are determined not to be received, or alternatively when analog TV signals are determined to be received, the first detector is conditioned for automatic fine tuning in response to the video carrier of received analog TV signal. The determination of whether or not DTV signal is received is made in response to the amplitude of DTV signal pilot carrier. The determination of whether or not DTV signal is received is made in response to the amplitude of analog TV signal video carrier or in response to the amplitude of intercarrier sound IF signal.
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