The Battle for Bandwidth

Oct 1, 2008 12:00 PM, By Steve La Cerra



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It's rare that the terms “pro audio” and “turmoil” are used in the same sentence. However, during the past 18 months, the wireless pro audio world has been in turmoil over the changes that will result from the FCC's frequency re-allocations that will take effect on February 19, 2009. Several different issues are in play simultaneously, the latest of which is that the U.S. Congress is contemplating a bill that would open up what are considered by many to be the “unused” portions of the frequency spectrum — aka, white spaces — for broadband use. The pro audio wireless industry faces a daunting challenge in maintaining its ability to run large-scale productions that rely heavily upon wireless equipment. Even as Mix prepared this article, new developments were literally happening on a daily basis.

A Quick History

Although licenses are required for wireless microphones, wireless audio gear transmits at very low power levels (averaging 50 milliwatts and maxing out by law at 250 mW). Add to that the fact that wireless mics do not broadcast 24/7 and that the FCC has basically ignored that there are millions of wireless mic users as opposed to the many other types of RF devices.

The licensing requirement was originally created as a means of tracking down cases of interference between wireless mic signals and TV broadcasts, but such problems never appeared. With decades of successful spectrum-sharing between wireless audio and TV broadcast, the FCC never set aside a specific UHF band for wireless mic applications as it has for aircraft communications, radio and TV broadcasting, cell phones and public-safety communication purposes. James Stoffo — who is frequency coordinator for the NBA All-Stars and Finals broadcasts, the Latin Grammy Awards and Billboard Latin Music Awards, and an entertainment RF technician for the Super Bowl — estimates that there are between a half-million and a million wireless mics in the U.S., but that fewer than 1,000 are licensed by the FCC.

Full-power, terrestrial analog broadcast television is scheduled to cease in the U.S. in February 2009, which means that analog TV will be obsolete and that the frequencies formerly used for analog TV will become available for other uses. This gives the illusion that there will be a lot of bandwidth available for competing technologies, but this is not the case.

Prime Real Estate

Lectrosonics' director of business development, Karl Winkler, reminds us that many people desire the UHF band for the same reasons. “The UHF band between 500 and 800 MHz offers excellent wave-propagation characteristics, as well as practical antenna size,” he says. “UHF can transmit over long distances with relatively low power. As frequencies get higher, it takes more energy to transmit the same distance and the wave is less able to penetrate through or bounce around objects. A ¼-wave antenna is very efficient for a UHF device, and at around three inches long that's very attractive. When you get into the frequency range higher than 1 GHz, antenna length can be even shorter, but you begin to lose the desirable propagation characteristics of UHF.”

Here Comes the Big Bad Wolf

Three major issues face pro audio wireless, two of which are already facts of life. The first is known as the “digital dividend.” Joe Ciaudelli, Sennheiser USA's consultant for professional products, explains, “The digital dividend is the re-allocation of the frequencies between 698 and 806 MHz, corresponding to UHF channels 52 through 69. Right now, television broadcasters are transmitting both analog and DTV signals. That ends in February of 2009, and when the analog channels are shut off, all TV broadcast will be consolidated below channel 52. This gave the government the ability to auction off channels 52 through 69. Verizon and ATT submitted winning bids on this spectrum, allowing them to secure these frequencies for a new class of consumer service after February 2009. This is a huge windfall for the government — they raised $19 billion. They were able to do this because DTV channels can be placed right next to each other, whereas analog channels required guard bands to prevent interference. When analog transmission ceases, DTV channels will be pushed closer together, freeing up the space from UHF 52 to 69. That is already a done deal.”

Stoffo elaborates on the second issue. “Strike two is the fact that a DTV channel is a complete 6MHz-wide burst of energy, and you cannot fit anything else inside it. If you picture a window of 6MHz spectrum, you can have an analog TV station in that space with one strong picture carrier and a separate sound carrier. Then, depending upon the strength of the TV station, you could also fit a couple of wireless microphones or in-ears in the white spaces [unused portions] of that window. DTV completely fills that window, so you must vacate that band entirely. This is why we are losing so much operational capability.

“Since 1962, we have had from 470 MHz to 806 MHz available for wireless microphone use — that's around 330 MHz of bandwidth,” Stoffo continues. “We lost 108 MHz of that bandwidth due to the auctions, and with DTV broadcast firing up, we lost half the remaining spectrum. The result is that we have approximately one-third of the bandwidth that was formerly available. A production like the Super Bowl requires around 1,500 RF microphones and we'll use close to 2,000 different frequencies. Trying to fit that into one-third of the bandwidth is going to be very difficult, if not impossible.”

The potential strike three, which Stoffo calls “the final nail in the coffin,” is legislation that the government is currently considering. “White space legislation — which has not yet happened — would open up the ‘unused’ UHF TV channels for broadband use,” reports Mark Brunner, Shure's senior director of public and industry relations. “That is why the FCC has been conducting tests on proposed white-space devices.”

During the summer of 2008, at the request of the Senate and the House of Representatives, the FCC began conducting field trials of proposed white-space devices. In theory, an approved white-space device would scan the local RF spectrum when turned on, identify the frequencies that are already in use and then choose a vacant frequency for its own operation. On August 9, 2008, the FCC attended a pre-season NFL football game in Washington, D.C., at FedEx Field. Prototype white-space devices were turned on and failed to scan the RF spectrum accurately for active wireless mics or TV channels. They also caused interference with the wireless mics already in use and failed to consistently recognize wireless mics that were turned on during the course of the game.

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