| 摘要 |
<p>2101644 9214343 PCTABS00015 An NTSC bandwidth-compatible HDTV system employs multiple quadrature amplitude modulation (QAM). A first suppressed QAM carrier is modulated (14) with high priority information including predominantly low frequency information. A second suppressed QAM carrier is modulated (34) with low priority information including predominantly high frequency information. The high priority QAM signal exhibits a larger amplitude and narrower bandwidth than the low priority QAM signal, and is disposed in the lower portion of the multiple QAM frequency spectrum normally occupied by the vestigial sideband of a standard NTSC television signal. The frequency spectrum of the multiple QAM signal (18, 20) exhibits signal attenuation at frequencies associated with high energy information in a standard NTSC signal, e.g., frequencies around the NTSC picture and sound carriers.</p> |
