Friday, February 20, 2009

DTV Transition For Wireless Mic Users

We're right in the thick of the digital television transition which started officially on February 17 and continues through June 12. But that is just the beginning of it for many wireless microphone users. The fact is that the airwaves are changing and some of that change might just knock you off the air.

The DTV transition is actually a shorthand way to describe a complete reassignment of the VHF and UHF frequencies that have been the domain of over the air broadcast television for some 50 years. The stated impetus is an upgrade in television from analog to digital broadcasting. But that's just the tip of the iceberg. If TV stations were only going to scrap their analog transmitters and replace them with digital transmitters on exactly the same channels, only TV viewers would be affected. But there's much more in play.

A second and perhaps more powerful incentive to make the transition is that over the air TV channels are being consolidated below 700 MHz. The upper UHF channels were sold off to other wireless service providers in a government auction. In addition, even the compressed television broadcast band is set to be shared to make more efficient use of scarce spectrum. All the channels that aren't filled with TV stations in any given area are available for use by other entities on a non-interference basis.

So what does this have to do with wireless mics? Many wireless microphones use equipment that jumped the gun on making use of those "white spaces" between powerful TV signals. They've been effectively squatting in the 700 MHz band without much of a problem. Their transmission range is short and the TV band never did fill up with stations. So interference problems were few and easily rectified by moving the mic in question to a different frequency.

All that is about to change. More TV stations are being crowded into the truncated UHF band. That leaves less room for multichannel wireless microphone transmissions, especially in larger cities. As soon as a new generation of white space devices approved by the FCC start moving into the remaining open channels, established wireless microphone users may find it tough to keep their preferred frequencies clear of interference. That could be a big problem for everything from theater productions to church sermons.

So what's a wireless mic user to do? Sweetwater, a major supplier of professional audio gear, offers a new guide called "Navigating the White Spaces" by Mitch Gallagher. It's an online resource available to read at no charge. If you are potentially affected by the DTV transition or just want to keep up with what is happening on the airwaves, it's well worth a read. Mitch outlines which microphones are affected (they all aren't), assessing your ability to continue squatting in the white spaces, and what other solutions are available. There are also links to additional guides and white papers published by the microphone manufacturers.

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