High Power Amplification of FM + HD Radio Transmissions with Elevated Sidebands
Tim Anderson, CSRE/DRB, CBNT, Manager, Strategic Radio Market/Product Development, Harris Corporation
Adding HD Radio sidebands at -10dBc presents many challenges to the transmission system. Space combined HD to FM signal level miss-tracking causes host interference issues and high level combining losses make 10% injection impractical. Common amplification is the most practical way to achieve -10dBc for HD Radio. At 10% injection, the RF inter-modulation products need to be suppressed an additional 10dB at the same time the power output is increased by 10dB. Linearity of the transmitter must be improved by 20dB to meet the original NRSC-5B RF emission mask. With all of the advances in solid state design, it would seem that the role of vacuum tube transmitter designs would diminish, but high power FM+HD requires higher efficiency and lower cost of operation that is best met with the novel use of a vacuum power tube. We will discuss the various combining methods available for HD Radio at elevated sidebands, Peak-to Average reduction techniques, the pro's and cons of solid-state vs. tube amplification and Harris' innovative approach to high-power common amplification using vacuum tubes.
