Reception and Distribution of Terrestrially Delivered Digital Channels in the Existing Analogue Environment

The forthcoming introduction of terrestrial digital television broadcasts while heralding a new era in television also ushers in a lengthy period of coexistence with the existing well established analogue system. — While this dual mode of broadcasting theoretically can be accomplished quite easily, the real world practical implementation can turn out to be somewhat more involved and problematic. — Utilisation of the adjacent unused guard band channel while providing for an efficient use of available bandwidth together with compatibility of existing receiving antennas and distribution infrastructure, does not however allow for the deviations often encountered. — Broadcasts emanating from one or more towers while of the same power do not necessarily translate to even levels in received signals at a reception site. — While antennas and associated distribution components all display a degree of uneven response over their operating bandwidth resulting in distortion of levels received from theoretically even field strengths, far greater and often unavoidable fluctuations can occur prior to reception of these fields. — The reliance on 10dB or more of level difference to provide protection to the analogue channel could turn out to be ineffective in numerous instances. Going by the differences in non-adjacent channels, with the expected similar propagation in the adjacent digital channel, protection can rapidly approach 0dB! — Together with the inheritance of over forty years of non-engineered and poorly installed distribution systems, the introduction of digital might not prove to be the simple task that the theory might suggest.

Published

1999-07

Content type

Original Research

DOI

10.5594/M001166

ISBN

978-1-61482-948-5