Enhancing Terrestrial High Power Transmitters by Application of Digital Signal Processing and Control

摘要

Until beginning of the eighties, most high power AM transmitters were of conventional design, equipped with many vacuum tubes, characterised by rather low efficiencies and high operating costs. The introduction of the tubed switch mode high level modulator (PDM) opened way to higher efficiencies and less power consuming modulation modes, like single side band operation (SSB) and controlled carrier transmission (DCC, DAM). But only since availability of digitally controlled, fully solid state modulators (PSM, pulse step modulation), a massive improvement in efficiency and modulation flexibility was possible. The pay back on reduced power consumption and lower spare parts and tube costs made the installation of such modern transmitters very profitable for the users. Also for the next decades the leading international broadcasters will use AM transmissions as a basic service for large area broadcasting and international long distance operation. They can rely on a new generation of sound broadcasting AM transmitters, either fully transistorised for medium power LF and MF service, or single output tube type for short-wave- and high power MF-, LF- broadcasting, offering extended performances based on low level digital processing and control. The report will review the latest state of the art of AM transmitting systems. Hence solutions for further improved efficiencies, increased flexibility and reliability will be investigated, and a principally new solution of feed forward control and system modelling technique allowing still better AF qualities and reduced unwanted radiation will be discussed. As another area of improvement, the computerised fully automatic operation of transmitting centres with optimum area and frequency control will be presented, relying on extendible modular control systems.