DTV transmission continues to be a conundrum for broadcasters: Spend the money to broadcast full power to serve a handful of DTV viewers or broadcast a low-power signal that saves on electricity bills but does little more than put a station in compliance with the FCC's DTV mandate.
As it stands today, most commercial stations seem to be opting for the latter.
"With the exception of public television, the whole issue of whether DTV is going to make money is a real issue," says Mike Kirk, vice president of communications for transmission-tube manufacturer E2V. "So, if commercial broadcasters are able to provide satisfactory service under the terms of their license without incurring a large power bill every month, they're going to do it."
The move to low-power DTV is more than a trend, according to Acrodyne Industries National Sales Manager Mark Polovick. "All the customers for all the vendors," he says, "are asking for 500-W, 100-W or 1-kW transmitters."
Transmitter manufacturers introduced a number of low-power DTV packages at NAB. But what should be bullish days for transmitter manufacturers are becoming as bearish as the rest of the nation's economy.
Says EMCEE Regional Sales Manager Jim Zaroda, "I think all transmitter manufacturers thought they would be rich by now selling high-power systems, and now they're all selling low power. The marketplace dictated to the vendors what [broadcasters] wanted, saying, 'If this is what we have to do, we want to do it as cheaply as possible.'"
Polovick notes that the market is very competitive right now. "If you're looking for digital low power, now is the time."
Axcera Director of Marketing Rich Schwartz sees interest in low-power transmission from stations looking to get on the air at the lowest possible overall system cost as well as those that want a system that can be upgraded to high power in the future.
While no one questions broadcasters' right to broadcast low power, some industry observers question the long-term impact. Because low power requires only enough power to cover a station's city of license or the grade A contour, they point out, many viewers within a DMA won't be interested in even attempting to receive an over-the-air signal. So much for a DTV-tuner mandate.
"If you go to the Best Buy or Circuit City, they aren't selling the DTV tuners anymore," Polovick point out. "So the issue of low power may, in fact, kill over-the-air because it doesn't help over-the-air digital be successful."
It's difficult to argue against the cost savings in transmitting a low-power digital signal. A study by EMCEE says that the electricity bill for operating a 50-kW two-tube inductive-output-tube (IOT) high-power transmitter for four years is about $306,000. For a 400-W, low-power transmitter, it's $11,200, a saving of approximately $295,000. EMCEE recommends a station begin with a low-power transmitter and upgrade to full power at a later date.
The savings of low-power transmission go beyond electricity consumption, Zaroda points out. The costs of the equipment, renting tower space and tower studies for large antennas are also lessened or eliminated. "It also allows [stations] to use the time during the low- to high-power transition to study their digital service," he adds.
Low power is attractive also for VHF stations that have a UHF digital allocation, according to Dave Glidden, director, television transmission products, for Harris. The reason? They haven't decided whether they'll stay with the UHF allocation or go back to the VHF slot.
Moreover, some stations purchasing low-power transmitters plan to use them in the future to help with signal extension, Schwartz says. "There are a fair number of stations that will need some signal-extension product in the future, a booster or a translator. They can use the low-power transmitter there, and then there's no fear that it's going to be obsolete."
One station using low power to fill in reception gaps is WPSX-TV Clearfield, Pa. Its UHF signal doesn't crawl over the hill into State College, Pa. So low-power transmitters make the crawl possible.
"Certainly, broadcasters in a similar situation will be looking into boosters, but there's also an application for boosters in terrain that isn't as rough and hilly," Schwartz says. "There will be pockets where a broadcasters who had VHF aren't filling in areas with the UHF signal."
Finances aside, there could be some new incentive to go full power. The FCC mandate to include DTV tuners in all television sets by 2007 gives broadcasters the comfort of knowing that the potential audience will have a predictable growth curve.
Also helping drive the move to higher power is a new development for transmitters with IOTs: multi-stage depressed collectors. An IOT is an electron vacuum tube that amplifies a signal by varying the density of electrons in a linear beam. A heated cathode supplies electrons, an anode accelerates them, and a grid controls the current or beam density. After RF output power has been extracted from the beam, the electrons (unused energy) are traditionally captured on a single collector at a wide range of energies, depending on signal level.
Multi-stage depressed collectors improve transmitter efficiency from 30% to 50%, resulting in significant savings in electricity costs. An over-simplified definition of efficiency is that an efficiency of 50% means that 50% of the power going into the transmitter exits the transmitter, 30% efficiency means that only 30% of the power going in leaves the transmitter.
The devices will be found in IOTs from manufacturers like E2V (formerly Marconi Applied Technologies), Northrup-Grumman, and Thales. They all have slightly different approaches to the technology, and that will prove a challenge to transmitter manufacturers that integrate the tubes into products for sale to broadcasters. Each approach offers a different degree of complexity and cost.
For example, the energy-saving collector IOT from E2V has three collectors (E2V calls them Energy Saving Collectors, Kirk says, because the word depressed
doesn't exactly instill consumer confidence). Because each collector captures electrons at a different voltage, more electricity savings can be realized than with a single collector.
Harris's Glidden describes the E2V approach as "plug-and-play," which means that the tube will be much easier to integrate into Harris transmitters. The Northrup-Grumman approach, he observes, is more elegant and promises higher efficiency but, because the collector has more stages, needs a more sophisticated cooling system, and that adds to the cost and complexity.
The design of the Thales single-stage depressed-collector tube is similar to E2V's but is a little simpler, according to Thales Sales Manager of Power-Grid Products Jim McVea, because it's a two-stage tube as opposed to a three-stage. It doesn't offer as much efficiency (hitting 48%) but is less difficult to integrate into an IOT.
"You get increased efficiency with multiple stages efficiency," he explains, "but each stage gets you less than the previous stage."
Like the E2V, Thales single-stage depressed collectors will be capable of being an upgrade for transmitters that use Thales tubes. "It requires some modification to the transmitter, the biggest one being a different beam supply," says McVea. "But the cavity is similar to what we have now, so [a manufacturer can make] just a few changes to the cavity and then put in a new tube. This gives the people that have our tube an upgrade path."
Northrup-Grumman's tubes, which have efficiency measured as high as 59%, will begin appearing in stations in the next two months, according to Buzz Miklos, director of sales and marketing for the Electron Device Division. Cost savings are just over $20,000 a year per tube for stations paying 10 cents an hour for electricity, he says, noting that savings depend on local electricity costs.
Astre Systems has two tubes that will be sent out to stations soon, and Thales (the transmitter manufacturing division, not the tube division) will be delivering one to a station in October.
E2V will get units into the hands of transmitter manufacturers later this year, Kirk says, adding, though, that they won't be quite as efficient as they could be. "Whatever tube we introduce needs to be simple in operation because the depth of RF engineering skills in the industry is diminishing," he says. "So you can't put a level of complexity into the transmitter just to save a few percentage points of power."
Glidden expects to have initial deliveries of transmitters with multi-stage depressed collectors sometime before next April's NAB show. Harris has yet to get its hands on a tube with the new collectors, but that will change in the upcoming months.
Just how cost-effective the new tubes will prove remains to be seen. According to McVea, it's really a matter of capital costs vs. operational costs. Stations concerned with capital costs will probably pass on the new tubes because tubes with the depressed collectors are expected to come at a premium. If the station's concern is monthly electricity bills, then the new tubes may be attractive.
Schwartz figures a larger-market station will more likely to go with higher power.
In a strangling economy, broadcasters may be looking to ride the low-power wave as long as possible. Says one transmitter manufacturer executive, "If the broadcasters could lower their analog power in the same way, my sense is we would sell a lot less full-power analog transmitters as well."
For now, the DTV transition could best be described as stuck in low power. And manufacturers see the next challenge in finding an incentive beyond mandates to get broadcasters up to full power.
"The medium- and small-market stations all tell me that DTV is an unfunded government mandate," says Zaroda. "They hate that because there is no return on investment and nothing on the horizon that says there will be."