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[Gregg Lengling]

We should mention here that, unlike klystrons, IOTs that use MSDC technology offer only a minimal efficiency benefit to NTSC stations – perhaps too little to justify the implementation cost. Eventually, DTV broadcasters may be able to choose five-stage, oil-cooled tubes, three- and five-stage tubes that are cooled with de-ionized water, or a three-stage tube that cools two stages with de-ionized water and one stage with air. All systems require a secondary cooling loop of water and glycol to port the heat to outside dry coolers. Five-stage tubes should operate at greater efficiency than three-stage designs, but may require a trade-off analysis of operating efficiency, system complexity and initial transmitter cost.

The first transmitters using MSDC technology are now coming online, and most IOT transmitter manufacturers will be shipping MSDC solutions within the next year, in time for stations planning to replace their initial low-power DTV transmitters with maximized UHF facilities.

Digital-ready analog systems
With the uncertain timing of analog TV's sunset, many stations are struggling to keep their aging analog transmitters operating because they cannot justify new analog transmitters.

For stations planning to revert to their analog channel assignment for DTV, one clear answer is to purchase a digital-ready analog system. Many manufacturers offer systems that can be readily upgraded to digital.

When the final channel selection choice is not clear, or if the station plans to stay with its current DTV channel assignment, a viable solution might be to upgrade only part of the older transmitter, or upgrade the transmitter in stages. For example, a broadcaster might replace an aging, unreliable control system with a newer one while keeping the existing amplifiers in service.

In some cases, stations and ownership groups might need additional versatility in their systems. Some of the newest transmitters are based on a single control and drive/amplifier cabinet that can be used as a stand-alone transmitter or as a driver for higher power systems, including high-power IOT transmitters. In addition, these new systems can convert readily from analog to digital operation. Such designs offer ease of upgrading and redeployment and can be an effective way to ensure that capital equipment remains in use for years to come.

New monitoring and control systems
Each year, the pool of qualified RF engineers is shrinking. For the remaining engineers, the need to operate multiple air chains and provide technical direction during the DTV transition is an ongoing problem.

But new approaches to transmitter monitoring and control are making it easier to manage complex facilities. While traditional systems required point-to-point connections and specialized programs, a new generation of control systems enables engineers to control transmitters using a standard Intranet connection and Web browser.

In addition to transmitter control, these new systems also provide Simple Network Management Protocol (SNMP) agents for real-time fault reporting and trend analysis. Performance monitoring provides oversight of transmitter spectral emissions, 8-VSB signal-quality monitoring, and control and metrics for linear and nonlinear adaptive correction.

As station groups implement more complex transmission plants with fewer technical resources, these advanced systems can also enable the transmitter manufacturer to provide enhanced remote diagnostic and repair services that further increase system reliability and lower operating costs.

The next step
While many challenges remain in the digital transition, broadcasters can choose among a growing range of technology and product advancements to ensure that the next stage of DTV is poised to operate efficiently and effectively while capturing the maximum possible audience. Be sure to discuss your upcoming challenges with your consultant or transmitter supplier as you plan your next step. Solutions to your transmission requirements might be easier and more effective than you think.

David Glidden is director of television transmission products at Harris' Broadcast Communications Division.