A Compatible Digital Audio Format for Broadcast and Cable Television

The addition of a digitally modulated carrier to the M-NTSC broadcast television signal would make it possible for television broadcasters to deliver digital audio and data. In laboratory tests, a QPSK carrier modulated with 512 kbits/sec of data has been added at a frequency of 4.85 MHz above the vision carrier. At a carrier level of -20 dB with respect to vision carrier, the new signal has been shown to be compatible with the BTSC stereo and SAP signals.