Transmitter May be Repack’s Silver Lining

Many TV stations — 800 or more — may have to move to new channels if the FCC’s incentive auction is successful this year and the agency repacks the TV band to accommodate wireless providers that will share the band.

The mass migration would be a big chore for the affected broadcasters as they would have to build new transmission facilities for each station. However, there would be at least one blessing — the opportunity to install a new breed of TV transmitters at the government’s expense.

Not only are the new transmitters more efficient than the first-generation digital units now in use, but they also are easier to cool and simpler to maintain — that is, less expensive to operate, according to the three transmitter manufacturers now serving the U.S. market.

What’s more, the vendors say, broadcasters will be able to upgrade the units to transmit the next-generation broadcast standard, ATSC 3.0, without much trouble if it becomes available in a few years.

“When broadcasters made the switch from analog to digital [in the 2000s], the only real option for high power was a tube transmitter like the IOT [inductive output tube],” says Cornelius Heinemann, VP, transmitter and amplifier systems, at Rohde & Schwarz.

Now, solid-state transmitters using modern Doherty amplification technology can provide a superior alternative, even for high-power UHF transmission, he says.

Efficiency is measured as the percentage of electrical AC power that is converted to RF power. Some of the high-power IOT transmitters that ushered in DTV in the UHF band delivered efficiencies between 15% and 18%, the experts say. Today’s solid-state transmitters exceed 40% efficiency.

Some solid-state transmitters are so efficient that the savings on power bills can pay for the initial price of the transmitter in about three years, says Rich Redmond, chief product officer at GatesAir. “In fact, we have some UHF transmitters approaching 50% [efficiency].”

Rivals Rohde & Schwarz and Hitachi-Comark report achieving similar efficiencies.

The electric bill is only part of the total cost equation, the vendors say. The dollars spent on cooling IOT-based transmitters are also significant.

But with solid-state transmitters, less electricity is wasted as the unwanted byproduct of heat, and the heat that is generated is easily dissipated by means other than costly air conditioning, Redmond says.

“With the advances of liquid-cooling, today you get air-cooled simplicity with liquid-cooling benefits in [GatesAir’s] Maxiva ULXT,” he explains. “It allows you to get the heat out of the building without running air conditioners.”

Heinemann agrees. “A solid-state transmitter with liquid cooled amplifiers and power supplies dissipates very little heat into the [transmitter] room.”

The solid-state units promise other operational savings. Tube replacements are expensive — upwards of $50,000, Heinemann says. While it is possible to extend the life of tubes, doing so “requires greater attention to the maintenance of the tube, which increases cost.”

What’s more, IOT-based transmitters require some specialized engineering knowledge that’s becoming harder to find.

“There are fewer and fewer technicians capable of tuning an IOT cavity, or working with the 32kV supply of the IOT, and their time will not be getting cheaper,” Heinemann says.

By comparison, training a broadcast engineer to troubleshoot a solid-state transmitter via a GUI is straightforward, and maintenance can be done without going off air, he says.

Maintaining a solid-state transmitter is also safer, says Redmond. “The voltage that tubes operate at is in the thousands and thousands of volts and generally requires a large beam supply outside of the transmitter building. In the case of solid state, they [the power supplies] operate at about 50 volts.”

Solid-state transmitters also require less physical space than an IOT-based unit. “If you are renting space, you can pay for less footprint,” Redmond says.

Finally, the biggest reason solid-state transmitters are more attractive is they are a reflection of a much larger trend in industry that’s seen tubes replaced with solid-state devices in everything from studio cameras to video processing devices.

“It’s pretty hard to go and buy a VHS tape recorder today,” Redmond says. “That doesn’t mean they don’t have some value to someone, but it’s a technology that the mass of people won’t adopt. Tube-type UHF transmitters are in a similar category.

“All across the board, it has been a matter of time [that solid-state transmitters would replace tube-based units], and that time is now. It just so happens to coincide with the repack in the U.S.”

Instead of buying a new transmitter, broadcasters could opt to re-tune their existing units to operate on their new channels.

However, doing so is not always practical. An analysis by GatesAir finds that “significant changes to transmitters” will be necessary if a station is moving more than two channel positions, says Redmond. Making changes also will be tough because components, such as TV amplifier devices, may be out of production, he adds.

Even in cases where a transmitter can be retuned, says Dick Fiore, CEO of Hitachi-Comark, which makes a line of Parallax Doherty solid-state transmitters, it will be incapable of operating as efficiently as today’s units. “Just because an existing transmitter can be retuned, does not mean that it should be retuned for the purpose of the repack.”

Running on a parallel track with the TV spectrum repack is development of ATSC 3.0, which, proponents say, will allow broadcasters to broadcast HD to fixed TV sets and mobile phones as well as data services in an IP format.

The Advanced Television Systems Committee is targeting 2017 for completion of the standard. But that’s just the first step. Broadcasters must also win regulatory approval before they put ATSC 3.0 on-air.

The upshot is that there is a good chance broadcasters will make back-to-back transitions — first to new channels in the repack and then a short time later to ATSC 3.0.

Upgrading the new solid-state transmitters to ATSC 3.0 should not be too difficult because they are based on OFDM technology used widely outside the U.S. say the transmitter makers, noting that they have been designing, selling and commissioning transmitters to support DVB-T2, ISDB-T and other OFDM-based TV standards for years.

To switch to ATSC 3.0 operation, stations would simply have to replace or update the transmitter’s exciter. At IBC 2015 last September, GatesAir launched its Maxiva XTE exciter. The new unit can be converted from 8VSB modulation to OFDM operation by loading new software, Redmond says.

Hitachi-Comark’s latest exciter, Exact, relies on field programmable gate arrays (FPGAs) to perform core modulation and correction functions. As a result, it too can be converted from ATSC 1.0 to 3.0 operation with a software update.

The one big downside to solid-state transmitters is that they cost more. But even that may be less of a problem because the government is picking up the tab. The experts say for transmitters in the 50 kW to 60 kW range, solid-state units will cost about 10% to 15% more than their IOT counterparts.

On behalf of the NAB, Digital Tech Consulting completed a study of various consequences and costs associated with the repack, including prices for different solid-state transmitters and their installation. It found the price of a 60 kW solid-state UHF transmitter to be $1.6 million; a 40 kW unit will cost $1.27 million; and a 5 kW plant, which would likely be used by a Class A station, will have a price tag of $127,500.

By congressional mandate, the FCC must set aside $1.75 billion to reimburse broadcasters for any costs they incur during the repack. That means that they may not have to worry too much about the capital costs associated with the repack, including the difference in the prices for tube and solid-state.

One caveat: the NAB believes that the $1.75 billion may be insufficient if more than 800 stations have to move to new channels. If 1,200 stations are assigned new channels, the total cost could soar to nearly $3 billion, it says.

If Congress doesn’t increase the reimbursement fund, broadcasters may not recover all their costs. The NAB is working to make sure the reimbursement is adequate.

Over the next several years, broadcasters will face many decisions related to the repack and new channel assignments. If what the vendors say is true, choosing what type of transmitter to employ may be one of the easier ones.

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