The Sky Isn’t Quite Falling, But...
By Gary Stanfill

Unsettled times ahead for wireless systems

At this point in time, most would agree that the digital television (DTV) “revolution” has been a bust in the United States. Consumers have not bought DTV sets in any great quantity, and most television stations are only slowly and reluctantly adopting DTV. So it’s no big deal, right?

The Sennheiser Evolution 300 Series offers eight user-selectable presets from a possible 1,280 over a 32 MHz range, making it a good hedge against future RF spectrum problems. PHOTO COURTESY SENNHEISER

Well, as the TV commercial says: not exactly. Despite the lack of support by consumers and the resistance of stations, Congress and the Federal Communications Commission (FCC) are moving aggressively to push DTV on the public. Simple reason: the expectation of billions of dollars flowing into the U.S. treasury when NTSC (analog) broadcasting ends, with the vacated frequencies then available to be auctioned off to the highest bidders. There’s also the little matter of significant campaign contributions that legislators are receiving from large companies hoping to profit in one way or the other from the DTV shift. In fact, it is more likely the changeover will accelerate than be delayed. Legislation has been proposed that would require analog broadcasting to end in as little as three years. Soon all new large-screen TVs must include DTV capability, and not too long after, all new TV sets must be so equipped. And the FCC is steadily raising the pressure on TV stations that have not embraced DTV.

DTV’s slow start has prompted many users of entertainment wireless systems (microphone, in-ear monitoring, etc.) to dismiss the “revolution” as a non-event. Until recently, only 200 or so DTV stations were on the air, and many were operating at such low power that they held little potential for serious interference with wireless systems.

However, at last count more than 850 DTV transmitters are now broadcasting, joining the nearly 1,700 analog transmitters already in use. Several hundred more DTV transmitters will be in operation by this coming summer, otherwise the stations risk losing their broadcast licenses. In addition, many DTV stations that initially were operating at low power are upgrading their transmitters to as much as 1,000,000 watts. As a result, the number of wireless users experiencing serious interference is growing daily.

Many popular wireless systems use the 788 MHz to 806 MHz frequency range (TV channels 67, 68 and 69). However, in Los Angeles for example, recent relocation of an existing analog station combined with a large increase in power output by one of the local DTV stations has reduced these three (formerly) usable channels down to only one. Many users are finding that they can’t use some (or all) of their existing wireless systems or are finding increased interference that is seriously affecting performance.

This isn’t the end of the bad news. It now appears likely that frequencies above 746 MHz (TV channels 60 to 69) will be converted to other uses within three years or so. While wireless systems using these frequencies will remain legal, as a practical matter, interference renders them unusable in some regions. Shortly afterwards, systems on frequencies between 698 and 746 MHz (channels 52 to 59) may well suffer the same fate.

Another problem is that while a vacant channel must be left between active analog TV channels, this is not necessarily the case for DTV. Thus we could soon see six or eight DTV channels stacked in an uninterrupted row, at least in some regions. Even frequency agile (frequency synthesized) systems may have trouble finding an open channel, already a problem in Los Angeles and a number of other larger cities where DTV channels are being slotted in between analog channels.

What are wireless systems manufacturers doing about all this? For starters, many are now offering systems on frequencies below 698 MHz, and increasingly with frequency agility that covers several TV channels.

In addition to providing switchable operation in the 470 MHz to 806 MHz range, Shure UHF systems also operate on the newer J4 and M4 bands, with a possible 24 compatible frequencies per band. PHOTO COURTESY SHURE

This will help protect purchasers of new gear, but pretty much leaves owners of older systems out in the cold. And despite what is likely to be a very limited useful life, equipment in the 746 to 806 MHz frequency range continues to be widely sold. Buyer beware. What does this all mean to you, the wireless user? First, it largely depends upon where you are, how much you travel and what gear you own. For example, frequency congestion is probably not going to become a problem any time soon in places like Wyoming and Montana. However, many TV channel assignments are likely to change, so if your systems are on single fixed frequencies, you could suddenly find a TV transmission right on top of them. Even so, a simple frequency change should fix the problem.

In major metropolitan areas, and especially if you travel widely, things are almost certain to become more difficult, and probably sooner rather than later. Within the next year, the vast majority of TV stations will be broadcasting on both an analog channel and a DTV channel, effectively doubling the number of TV stations. Further, a large number of DTV transmitters will increase output from a token 2,000 watts (or so) to the authorized 25,000 to 1,000,000 watts. At the same time, DTV stations already in operation may change their channel assignments without warning.

The bottom line is that finding usable frequencies is going to get considerably more difficult in many areas of the U.S. Wireless systems that have worked well and been trouble free at all venues/locations in the past may no longer operate problem-free in some locations. Obviously frequency agile systems make it considerably more likely to find clean frequencies. But users of older fixed frequency units could soon find themselves more or less out of luck.

What to do? First, come to grips with the idea that DTV is going to happen and that it will probably have at least some impact on wireless use. Second, understand that new wireless gear may well be in your future, even if you’re perfectly happy with what you own/use now. Finally, accept the fact that using wireless is likely going to involve more work, and be less predictable, than in the past.

Faith Hill performing recently with a Sennheiser SKM 5000 outfitted with Neumann KK 105 S mic capsule.

Also keep in mind that your mileage may vary. Some fortunate wireless users working in just one area, with only a few systems, all of which happen to be in the right frequency range, may get off pretty much unscathed. Others not so lucky may need to delay the purchase of those nifty new subs and instead budget for new wireless systems. Most users will experience some level of extra difficulty on an ongoing basis. Do you need to purchase new wireless gear now? Not necessarily. Existing systems can certainly be used as long as they do the job. But there should be a backup plan in place in case of sudden “crash and burn.” Just because systems worked perfectly at a venue last year doesn’t mean they’ll fare the same this time around. Best not to wait until the last minute to make sure systems are going to work - leave time to rent, borrow or buy other systems, or (heaven forbid!) to set up wired mics.

When purchasing new wireless systems, spend the extra money to get quality frequency-agile equipment that can be tuned over several TV channels. Don’t fall for “features” - instead, look at solid RF (radio frequency) performance and wide range tuning. The extra TV transmitters jammed into a limited frequency range is certain to increase potential for other types of interference such as intermodulation (intermod), so make certain that your new equipment can handle this. Some inexpensive wireless systems simply can’t.

It would also be wise to consider systems operating between 524 and 698 MHz (UHF TV channels 23 to 51). In many cities, UHF TV channels 14 through 22 are already shared with two-way radio and other users. And sooner or later, all TV channels above 51 are going to be assigned to two-way radio or auctioned off for other noncompatible uses.

While the sky is definitely not falling, it is starting to rain a bit. Don’t be caught unaware and unprepared. Do the homework and take the necessary action - you should be able to successfully use wireless systems for many years to come.

The FCC web site (www.fcc.gov/ mb/video/tvq/html) is a resource that can help in the planning of wireless use ahead of time. It lists current and planned TV stations anywhere in the U.S., and it is a good resource to determine if your existing gear is likely to experience interference in a particular region. This information can also be helpful in selecting the frequency range of any new equipment you are considering buying. In addition, the current status of the DTV conversion may be found at www.fcc.gov/mb/ video/files/dtvsum.html.

Gary Stanfill has more than 30 years experience in audio, RF technology, communications and wireless systems. He served as president and general manager of Vega, and is now principle consultant for Colmar Systems, based in Southern California. Gary can be reached at gjstanfill@earthlink.net.