Performance characteristics of an MSDC IOT amplifier

The design and performance of an inductive output tube (IOT) based amplifie r incorporating multistage depressed collector (MSDC) technology is summari zed in this paper. The amplifier performance goal was to provide an enhance d efficiency rf amplifier for the UHF digital television broadcast market. The operational frequency of the amplifier is 470 to 820 MHz. The design em phasizes simplicity to minimize upgrade requirements fur existing digital t elevision 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 i ncorporates three elements with one element serving as a depression stage. The collector design curtails the reflection of spent beam electrons back t o the IOT interaction gap and minimizes the generation of secondary electro ns at critical collector surface locations. Testing emphasized the 8-VSB mo dulation scheme adopted bu the ATSC for digital television broadcasting. Pe rformance results indicate that the IOT electrical efficiency increased fro m 34% to 51% with the addition of MSDC collector when the amplifier is oper ated at 15 kW average rf power using the 8-VSB modulation scheme.