Performance characteristics of an MSDC IOT amplifier

The design and performance of an inductive output tube (IOT) based amplifier incorporating multistage depressed collector (MSDC) technology is summarized in this paper. The amplifier performance goal was to provide an enhanced efficiency rf amplifier for the UHF digital television broadcast market. The operational frequency of the amplifier is 470 to 820 MHz. The design emphasizes simplicity to minimize upgrade requirements for existing digital television transmitter designs and insure a low cost IOT. The enhanced efficiency IOT is based on an existing standard collector IOT capable of providing peak envelope powers of 60 kW. The collector design incorporates three elements with one element serving as a depression stage. The collector design curtails the reflection of spent beam electrons back to the IOT interaction gap and minimizes the generation of secondary electrons at critical collector surface locations. Testing emphasized the 8-VSB modulation scheme adopted by the ATSC for digital television broadcasting. Performance results indicate that the IOT electrical efficiency increased from 34% to 51% with the addition of MSDC collector when the amplifier is operated at 15 kW average rf power using the 8-VSB modulation scheme.