Automatic phase adjustment in coherent TV carriers - in accordance with phasing pattern corresp. to barker codes by using IF with continually changing phase

摘要

To avoid high summation peaks resulting from a number of modulated TV carriers using the same transmission line, measures such as setting up a fixed phase relationship between the carrier waves are insufficient. It becomes necessary to provide for a continual automatic adjustment of the phases in order to reduce to a minimum inter-and cross modulation interference. The invention prescribes a method for setting the phase relationship of neighbouring carrier channels in accordance with a phasing pattern that corresponds to the Barker Codes characteristic for Pulse Compression codes. This is achieved by including into a frequency conversion channel (AX) a phase regulator loop (PLLS) which is controlled by a phase setting member (PE) and the input from another generator (fo). An intermediate frequency generator (ZG1), for example at 38.9MHz, is applied to the sending converter unit (ZF/HF) as well as to the modulation circuit of the receiver unit phase setting stage (PLLE). By means of a mixer stage contained in the regulator loop (PLLS) the thereby generated intermediate frequency has a continually changing phase which is compared with an intermediate frequency of a reference carrier pair, and the result is used to modify the phase of Ax as well as all neighbouring channel pairs until the total phase pattern corresponds to the optimal distribution over the carrier bundle.