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RF Technology at NAB Show Reflects Changing Broadcast Spectrum

Transmitter companies haven't been just sitting still while waiting for orders to come in from stations changing channels after the FCC's incentive auction plan. At this year's Las Vegas NAB Show I observed more efficient TV transmitters--along with broadband antennas and tunable filters--that should make it easier for stations to change UHF operating frequencies in the future.

GatesAir (formerly Harris Broadcast) showed a new Maxiva UHF transmitter that’s can deliver 27.5 kW (pre-filter, ATSC 8-VSB) and was housed in a single tall rack. The Maxiva ULXT with PowerSmart 3D provides power equivalent to that from an IOT amplifier, with an efficiency exceeding conventional IOTs and even approaching what’s available with MSDC IOT amplifiers.

VHF TV broadcasters, looking to overcome problems with inefficient receive antennas and interference from energy-efficient lighting devices, switching power supplies, computers and other consumer electric and electronic gear, are attempting to increase coverage by adding vertical polarization and increasing power. GatesAir showed a VHF high-efficiency amplifier, the Maxiva VAX with PowerSmart 3D that provides AC-to-RF efficiencies of up to 48 percent (ATSC) and can operate throughout the entire high-VHF band without retuning.

To achieve this performance, GatesAir engineers have developed their own twist to Doherty amplifier technology--"PowerSmart 3D"--that provides Doherty efficiency with broadband performance. (The "3D" refers to "3 Devices.") When I asked about the technology I was referred to the company’s patent covering it.

Several other companies showed high-efficiency UHF transmitters with Doherty amplification. Comark demonstrated a new transmitter that’s able to output 15 kW (ATSC pre-filter) per rack. Comark has also made some improvements to its popular DCX Paragon MSDC IOT transmitter to improve efficiency.

Broadband amplifiers are nice, but stations faced with a channel change after the incentive auction will not want to have to replace mask filters or antennas. As a way around this, several manufacturers showed tunable mask filters. One that caught my attention was the RFS 25 kW tunable UHF unit. This will be an ideal match for the new high-efficiency UHF solid-state amplifiers or single IOT amps. RFS also showed two fully enclosed broadband panel antennas in relatively small packages, as compared to conventional discrete panel designs.

I'll have more on transmitters, filters and antenna from these and other manufacturers, along with some other interesting RF products and information on GatesAir's PowerSmart 3D amplifier, once I track down the patent, in my next RF Technology column in TV Technology magazine

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.