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.

White Spaces Debate Outs Wireless Mics

One perhaps unexpected consequence of the increasingly heated discussion over the "white space" TV band spectrum is the outing of "unauthorized" wireless microphone users, such as churches, theaters, corporate lecture rooms and so on. It turns out that many of them have been squatting on unused UHF TV channels for years with nobody being the wiser. Now they'll have to vacate or risk being crushed like bugs by the winners of the 700 MHz spectrum auction when new services start moving into the old analog TV channels next February. What's more, it's becoming increasing less likely that they can simply re-tune their transmitters and quietly slip down into gaps between the new digital TV (DTV) channels.

Wireless microphones are one of those clever technologies that have become insidious over the years. You see them everywhere there is any type of vocal performance. Those microphones you see on televised concerts that don't seem to have any wires connected? That's them. A lot of times you don't even notice the mics. Ever see a microphone pointing at someone on a TV news show? The host and the guests are just chatting like they were in your living room, but you never hear any background noise. They're wearing wireless microphone packs with tiny mics on their lapels. Broadway shows are also extensive users of wireless mics, so that you can hear every nuance of the performance without the actors having to scream. Even your pastor may be using a wireless microphone on Sunday to be able to move around during the sermon.

So if this technology is so insidious, what's the problem? It seems to work just fine. Yes it does, but what you don't realize is that the frequencies many of those wireless microphones are transmitting on are supposed to require a government license and are only for specific types of users. They are regulated as low power auxiliary stations under FCC rules Part 74, subpart H. The key word is "stations." These devices are considered to be lower power radio stations. This part of the rules covers broadcasters, and these auxiliary stations are supposed to be for the use of broadcasters, radio and TV networks, movie and TV program producers, local distribution networks, and cable system operators that produce their own shows.

Oops! No mention of churches, theaters, schools, concerts, lectures, dance clubs, performing arts centers or the like. Yet, they all use wireless mics. So why hasn't the long arm of the law come after them? Mostly because they haven't been causing a problem. There was so much unused space in the UHF TV bands and these devices run such low power that there just wasn't an interference issue. That's about to change.

First thing that will happen is that the new owners of the upper UHF TV channels from 52 to 69 will move in with high power equipment for mobile broadband and other services. Considering the billions spent to gain this valuable spectrum, the chances of large blocks staying quiet are about nil.

On top of that, Google is mounting a public relations campaign called "Free The Airwaves" to drum up support for turning the remaining white space spectrum between DTV channels into unlicensed usage across the board. That would legitimize the continued use of wireless microphones for all performers, but interject the new problem of interference and lots of it.

So what's a poor wireless mic user to do? There are some other frequencies already available for this use. But "broadcast" quality equipment, especially systems that can support many simultaneous microphones, is scarce and unused channels even harder to find. There's also the issue that thousands, perhaps as many as a million 700 MHz wireless microphone systems are already in the field and will be inconvenient and expensive to replace. That argues strongly for protecting at least some of the new DTV spectrum below 700 MHz for wireless microphone usage. Perhaps a good long term solution could be found like the creation of the Wireless Medical Telemetry Service for hospital equipment that might otherwise be a white space squatter.