At the NAB Show, several transmitter manufacturers were showing new UHF solid-state DTV power amplifiers that were more efficient, cost less and occupied less space. Axcera showed a 10 kW average output power solid-state DTV transmitter in one rack. The transistors were covered so it wasn’t possible to determine what devices they were using. The transmitter should be available later this year. While amplifier design, choice of materials and combining systems can increase power and improve efficiency, there is at least one new transistor that could make it easier for manufacturers meet these goals.
Transmitter engineers are used to seeing tube companies at NAB and you may remember the Cray Semiconductor display of amplifiers using silicon-carbide transistors several years ago. This year, Freescale Semiconductor introduced an LMDOS RF power transistor capable of delivering up to 450 watts peak output per device. Freescale claimed its MRF6VP3450H offered “the highest output power in its class for UHF applications,” along with reduced power requirements that could potentially save users “thousands of dollars” in power bills.
Typical power gain in DVB-T operation at 50 V is 23 dB, with a drain efficiency of 28 percent and an average power output of 90 W. The output power would be higher for ATSC, which has a lower peak to average ratio than DVB-T. The transistor is capable of handling a 10:1 VSWR at 50 VDC and is designed for push-pull operation.
“As energy costs continue to soar, the ability to use highly efficient, cost-effective TV transmitters is critical to broadcasters,” said Gavin Woods, vice president and general manager of Freescale’s RF Division. “Transmitters designed with our new MRF6VP3450 device not only deliver dramatic annual energy savings, but also can significantly reduce transmitter cost by helping to minimize the number of required RF power transmitters.”
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