In a transmitter/encoder system for processing a widescreen television signal having main panel and side panel information, side panel luminance information and side panel "Q" color difference information modulate one phase of a quadrature modulated 3.58 MHz auxiliary subcarrier, other than the standard NTSC chrominanced subcarrier, having a field reversing phase characteristics. the other (quadrature) phase of the auxiliary subcarrier is modulated with side panel wideband "I" color difference information. The "I" modulated component is filtered by an inverse Nyquist slope filter which mirrors the filter characteristics of Nyquist slop filter used at a receiver/decoder to achieve a desired flat amplitude response when the signal component containing the side panel luminannce and "Q" color difference information is demodulated.