A Frequency-Domain Interpretation of Echoes and their Effect on Teletext Data Reception

The interpretation of echoes in terms of ripples in the amplitude and group delay of a system is analyzed and discussed. Simple relationships are given, valid for most practical purposes for echo levels up to at least 10-20 percent. Scre general applications are considered, including determination of SAW filter triple transit frcm group delay ripple rate and amplitude. For this paper the relationships were used to represent echoes due to multipath. A computer program for television system analysis used these echoes as an input and eye diagrams were plotted for different echo levels and tines, for both ideal and real systems. Computer simulation of a data decoder, which extends the analytical approach to include direct assessrent of errors as a function of decoding threshold, is described but not used herein. Ihe analytical approach appears to be promising and will be applied to a greater number of echo and real system combinations as time permits.