By John A. Pranke, Theta-Com
When the present television channel assignments were made by the FCC in 1952, the visual carrier frequency tolerance was specified as ± 1 KHz, with provision for a± 10KHz offset where necessary to minimize co-channel interference. These assignments have, with exceptions, proved satisfactory for twelve channel reception and cable transmission, since all second order products fall out of band and the magnitude of triple beats had not been a limiting factor. Recent industry efforts to standardize on a channeling plan for expanded channel systems and an off air, cable compatible receiver have pointed out a number of problems with the present transmission assignments. This paper reviews the various plans proposed within CTAC and other organizations, their advantages and limitations, and concludes that operation of broadcast transmitters on precise frequencies or phase locked to a national standard could effect a major improvement in off air and cable television performance. Methods to achieve such frequency control are also reviewed.