Compatibility tests on FM multiplex broadcasting for mobile reception have been done. Causes which generate interference in receivers have been unveiled. First, the characteristics of various kind of receivers have been measured multiplexing MSK signals with the existing sound signals. Second, the interference which is caused by the multiplexed signals under multipath propagation have been measured in indoor tests. Third, after the end of daily FM programs, the test signals multiplexed by L-MSK method have been broadcasted from NHK FM Tokyo (82.5MHz) station. The audio impairment by L-MSK signals has been surveyed by questionnaire. The minimum injection level of L-MSK has been decided four percentage as results of detail analyses.
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