A system for transmitting digital programming includes a program source
providing digital information, circuitry for modulating the digital
information onto a visual carrier modulated with analog television
programming, and a visual transmitter coupled to the modulating
circuitry. Using a phase modulation method, the system phase modulates
the digital information onto a visual carrier, reduces the baseband
frequencies of the phase modulated visual carrier, and amplitude
modulates the phase-modulated video carrier onto a video signal. The
amplified and encoded video signal are combined with an amplified sound
signal and transmitted. Using an additive method, the system modulates
the sidebands of the video carrier with the digital information and
amplitude modulates the video signal onto the video carrier. The
data-modulated sidebands are phase-shifted such that they will be in
quadrature with the amplitude-modulated video signal. The system combines
the amplitude-modulated video carrier and the data-modulated quadrature
sidebands. With a blended multiplicative/additive method, the system
provides phase modulation and quadrature sideband addition to provide an
optimized result.