An improved high efficiency 500 kilowatt short wave broadcast transmitter with novel features

Some of the changes in international broadcaster's HF (high-frequency) transmitter needs are addressed, along with some adaptations in HF transmitter design to reflect those needs. The authors identify three fundamental changes in the emphasis of international broadcast transmitter requirements: due to increasing energy costs, more emphasis has been placed on equipment power efficiency; due to increasing labor costs, more attention is being paid to automation and ease of maintenance, i.e. manpower efficiency; and, third, because of spectrum crowding, improved spectral occupancy has become a concern, particularly with respect to transmitted signal purity, and spectral-efficient modulation modes. Several developments designed to meet these needs of broadcasters are described. The issue of power efficiency has been met with improved transmitter RF and modulator circuits. RF efficiency has been improved in part by lowering losses in RF output coupling circuits. This improvement is afforded by better network design, and better automatic tuning, i.e. tuning for best efficiency. More efficient RF output tubes have also been developed. >