In the present invention, an ancillary code is added to a composite video signal in its active video portion. The ancillary code may be spread over several frequencies and summed at the output of a decoder to enhance the legibility of the ancillary code at the output of the decoder. Frequency-stepping...http://www.google.com.mx/patents/US5737025?utm_source=gb-gplus-sharePatent US5737025 - Co-channel transmission of program signals and ancillary signals
