Upbeat About Depression

The impetus in transmission developments continues to be improved efficiency, and manufacturers look to next-generation technologies like multi-stage depressed-collector transmitters as a way to show gains in both digital and analog transmission.

Ai, for example, is introducing the QVC line of multi-stage depressed-collector (MSDC) transmitters available in three-stage or five-stage tubes. Part of the Quantum lineup, it retains many of the original features found in the Quantum roster, despite a potential problem with space constraints.

"The first thing we did was get rid of the crowbar circuit because the Quantum family step-start switch doesn't require it," explains Ai National Sales Manager Mark Polovick. "We have no crowbar in any of our digital products, which are water-cooled and offer 60% efficiency in the five-stage version and 55-plus% efficiency in the three-stage."

The decision to go with a water-cooled system came about when options like oil or Glycol showed problems. A dual-loop system is mounted on the wall outside the transmitter so that water runs through the coil on one side while, on the other, Glycol runs through the loop. Polovick says that allows the Glycol to stay outside the transmitter while still removing any worries of freezing.

"In order for the water inside the transmitter to freeze, it would have to be off for hours and hours," he says. "Plus, when water gets heated, it just boils while tube manufacturers have told of us of instances where the oil will burn."

Polovick says that, when Ai realized the efficiency gains possible with depressed collectors for DTV transmission, it decided to build an NTSC model as well.

Also introducing an MSDC transmitter is Thales. The company says the DCX Paragon MSDC IOT digital transmitter has efficiency up to two times a conventional IOT and four times that of a solid-state transmitter, resulting in cost savings of 50% to 75%. The company says that translates into power bills of up to 50% to 75% less than conventional products sold for digital transmission today.

On the low-power side, Thales will show its Affinity, available in both ATSC and DVB versions.

Axcera is offering a new MSDC option for its Visionary digital transmitter. The option is for a standard IOT available in three- or five-collector versions, a choice of water or oil cooling, and digital or analog.

Not all manufacturers, however, are sold yet on MSDC technology. Dave Glidden, Harris director, television transmission products, says MSDC is a very attractive product idea for customers because of increased efficiency but a heavy push by manufacturers is a bit premature. "There isn't one manufacturer that is in full-scale production of tubes, and there is only one manufacturer in preproduction. There's a risk a change in specs that could affect design."

Harris is currently figuring out a proper MSDC design, he says, which should be available by NAB 2004. For now, his advice is to purchase a Harris low-power Ranger transmitter and then install the MSDC full-power unit when it's available and proven. The station then can use the Ranger as a backup.

Glidden says the NTSC market has found renewed legs as broadcasters realize that the 2006 shutoff for NTSC won't happen. Harris will demonstrate new low-power NTSC transponders developed jointly with its subsidiary Hirschmann Technologies, based in Austria. They're available in 2-kW to 30-kW solid-state versions.

Axcera also is addressing low- to medium-power transmitter needs with the Pioneer line, which uses the latest LDMOS devices in a compact package for both analog and DTV applications. It's available for power levels from 10 W to 6 kW analog and up to 3 kW for DTV applications. Rich Schwartz, Axcera director, marketing and product management, says the product-development cycle involved a lot of input from customers.

The transmitter is modular in design, with broadband amplifiers covering the entire UHF band, the key to making the range of power levels available. The design also makes it easy for stations whose channel is out of the core or is expected to be displaced in the future to retrofit.

New antennas also will be unveiled at NAB. Dielectric is introducing the TLS-V high-band VHF (Band III) pylon array in four-, eight- and 12-bay configurations for ERP levels in excess of 200 kW. It has extremely low windload and weight characteristics (75% less windload than comparable-gain panel antennas) and can be used for both analog and digital broadcasting.

Dielectric also introduced low- and mid-band VHF models of the DTV CIF mask filter. The company says it offers high out-of-band rejection characteristics, adjacent-channel-combining capability in a temperature-stable design. A directional UHF filter and DVC Series high-band VHF branch combiner are also available.