December 22, 2008
The Use of Wireless Mics in the U.S. Beyond the DTV Transition
The sky may not be falling; it's just really cloudy!
by Peter Schneider

As 2008 comes to a close, the biggest upheaval our industry has seen are the changes to the RF spectrum. The effect will have far-reaching consequences as sound mixers get squeezed into ever shrinking patches of available frequencies. This article will attempt to explain how we got here, and what our options are looking beyond next year.

The History of Wireless Mic Legislation
In the United States, the FCC is, "charged with regulating interstate and international communications by radio, television, wire, satellite and cable." This includes wireless mics and any other wireless equipment used in our industry, including IFBs, video assist devices and intercoms.

The following sentence may come as a surprise: If you are using any of the aforementioned devices without an FCC license, you are breaking federal law, specifically operating in criminal violation of 47 U.S.C. 301. Before you rush to your local police precinct to turn yourself in, consider that there are countless thousands of us violating the same law in the same way, and the FCC has, at least prior to this year, turned a blind eye.

In the late 1970's, as wireless microphones were becoming somewhat reliable for production use, television broadcasters petitioned the FCC to allow them to use frequencies within the TV broadcast spectrum on a secondary, non-interfering basis for "low power auxiliary" use. Over the years, the eligible groups have been expanded to include television and motion picture producers, which the FCC defines as, "a person or organization engaged in the production or filming of motion pictures." Fortunately (or unfortunately, depending on your perspective), they don't get more specific, because these days almost anyone who owns a video capable cell-phone and a YouTube account qualifies as a "producer".

So, at least most of you reading this are *eligible* for a license. There are, however, currently over a million wireless mics being used that are *ineligible*. Think of every house of worship, every public speaking event, every boardroom, every classroom, every concert and every theatre (including Broadway) that you've been to where wireless mics are used illegally without even a hope that the users could get a license.

And while the number of wireless mic users grew exponentially, the number of instances of interference, both with other wireless microphone users and to television signals and public safety communications (both of which would be a huge red flag for the FCC) are insignificant. This is due to the nature of wireless microphones: relatively low power and high bandwidth (which makes them more likely to be the target of interference than the cause of interference), wireless mic users practice a combination of self-interest and self-policing - we can't transmit on an occupied TV channel because chances are we won't get more than one foot of range.

So, what exactly was the FCC's position during this incredible growth of wireless mic users? John Nady, CEO of Nady Systems, summed it up very eloquently in his recent FCC filing:

"...For over thirty years. the FCC has known about unlicensed wireless microphone use in the TV spectrum for purposes not authorized by regulation and has tacitly allowed that use to continue....The FCC's policy of benign neglect toward unlicensed wireless microphone use in the TV spectrum has allowed the wireless microphone industry to develop technologically, fill a market need, enabled prices to come down as a result of volume production and opened up the benefits of wireless microphones to professionals not limited to the TV radio-motion picture industry."

The Spectrum Squeeze
In fact, this policy could have worked for the foreseeable future, were it not for other, more powerful market forces that also wanted use of the unused TV spectrum.

The squeeze began gently in the early 1970's when frequencies between 470-512MHz were made available to Land Mobile Radio use (walkie-talkies and repeaters) in eleven cities. This use was expanded in the mid 1990's with priority given to public safety users, and is referred to as the "T-Band" for it's use of television channels 14-20.

The squeeze continued to tighten in the 1990's, when the NTIA Radio Astronomy Service prohibited transmissions in TV 37 (608-614).In addition, the FCC allowed wireless medical telemetry devices to transmit in-hospital patient data in the unused TV spectrum, and additionally allocated 24 MHz between TV channels 60-69 to public safety.

Of course, it's the Telecommunications Act of 1996 and its provision for "Advanced Television Services", that squeezed us out of the most spectrum. Designed to rapidly accelerate "private sector deployment of advanced telecommunications and information technologies and services to all Americans" in part by mandating broadcasters switch to DTV service, wireless mic users lost literally half of their available spectrum as broadcasters began simulcasting in both analog and DTV formats.

Incidentally, wireless mic users were not the only group affected by the DTV transition. On February 27, 1998, WFAA-TV of Dallas, TX began broadcasting it's test DTV signal, and within minutes alarms were ringing in the recovery wards at Baylor University. Medical Center located some 18 miles from the transmitter. It turns out that Baylor's wireless medical telemetry devices (specifically their heart monitors) were using the same TV channel that WFAA-TV was assigned for DTV transmission. Station engineer Wayne Kube compassionately declared, "We would have the right to go back on the air immediately, but we would hate to cause anyone any harm." Luckily, no one was hurt, and the FCC would eventually allow these devices to operate in TV channel 37.

With the transition to DTV, Americans were promised a "Digital Dividend" - spectrum that could be opened by moving DTV assignments below 698 MHz. This newly available spectrum between TV channels 52 and 69, along with other "Advanced Wireless Services", would in the words of FCC Commissioner Deborah Taylor Tate, "provide all our citizens the vast opportunities of the broadband world of today so they may compete in the global economy of tomorrow." This spectrum began being auctioned off in 2002 and again in 2003 (where, for example, Qualcomm grabbed TV channel 55 for their "MediaFlo" TV service seen on some Verizon's phones) and culminated in the infamous 700 MHz "Auction 73". All told, the auctions netted the US Treasury about $20,000,000,000 - or just under 25% of the AIG bailout.

Hey Verizon Guy, Wanna Buy my Block 28 Radio Mic!?
The FCC's plans for the rest of the 700 MHz spectrum were well known by the summer of last year, and the auctions themselves started in January 2008. The auctions were for a combination of nationwide, regional and local broadband and narrowband (voice) services.

Here's how it panned out:
Various AT&T AT&T Qualcomm Qualcomm Various AT&T AT&T
D Block Public Safety  
D Block Public Safety  
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69
698 MHz 806 MHz

Note that the "D Block" never met its reserve price, and so consequently didn't sell at auction. The FCC has since de-linked it, and is scheduled as Auction 76, with no dates given.

In New York, Verizon, Qualcomm and AT&T were the big winners, and nationwide these three spent a combined sixteen billion dollars. It's hard to imagine that they would sit on this investment - both ATT and Verizon announced that they will conduct tests as soon as possible, and plan substantial deployment by 2010. In any case, it seems reasonable to assume that at some point next year, things will start to get ugly for wireless mics attempting operation above 698 MHz. First to go will no doubt be TV Channel 56 - remember this was won by Qualcomm and will be used to augment their existing Media-Flo service. Barring any major economic meltdown of the other auction winners, build out will happen at a relatively brisk pace.

As Henry Cohen of Production Radio Rentals stated in his talk here at Gotham in June, "What will probably happen though is if you just spent $7 billion for some spectrum, you're going to call up the FCC and you're going to petition and you're going to say: 'get these people out of here. We don't want any secondary users in our spectrum.'" Less than two months later, the FCC responded to a petition from the Public Interest Spectrum Coalition, an ad-hoc coalition of groups whose Board of Directors reads like a who's who of new media, by announcing that they were intending to, "revise our rules to make clear that low power auxiliary stations authorized under Part 74 of our rules – including wireless microphones – will not be permitted to operate in the 700 MHz Band after the DTV transition."

One important distinction to make is that the FCC's filing merely announces the Commission's intention. It is not yet law. As Sennheiser put it in their response, "This is far shorter notice than the Commission has ever given for the discontinuation of any product. Even manufacturers of devices known to cause actual harmful interference have invariably been given more time to cease marketing, and users were allowed to continue operating indefinitely...the proposed transition is unnecessarily harmful to the industry and to customers who bought the equipment in good faith long before the Commission announced any action."

Sennheiser, Sony, Shure and Lectrosonics announced as early as October of last year their intention to stop regular production of units on those frequencies (we notified our customers about this in a newsletter sent out in December 2007).

White Spaces Make Strange Bedfellows
In 2004, the FCC proposed "smart radios" that would provide wireless, high speed access to public and private networks that could utilize the white spaces in the TV spectrum - the same unused TV channels that wireless mics use. As of today, there have been nearly 35,000 comments filed with the FCC about these "TV Band Devices or TVBDs" (also known as "White Space Devices"), with performers, preachers and casinos, including such luminaries as  Dolly Parton, Guns 'N Roses, Joel Osteen and Harrah's on one side and companies like Dell, Google, Intel and Microsoft (all members of the "White Space Coalition") on the other.

For four years, the FCC attempted to balance the interests of the computer industry and politicians with those of broadcasters, entertainers, cellular companies and everyone else who relied on predictable, clear spectrum in the TV band. Depending on who you listen to, TVBDs represent either the democratization of high speed Internet access, or the end of filmed and live entertainment, news and sports as we know it, or both.

As veteran RF engineer James Stoffo says in his comments to the FCC:

The FCC states that it proposes to allow the use of unlicensed devices “to operate in the broadcast television spectrum at locations where that spectrum is not being used”. After twenty-five years of RF experience and working in the live television business, there is no such place in any major city in the United States.

In fact, wireless microphone users have become the flash point not just between old media and new media, or even between the haves and have nots of broadband internet access, but of the changing trends in spectrum management. The FCC was formed in 1934 out of a need to regulate the airwaves and act as planning authority to promote efficient use of scarce RF spectrum. This "central planning" policy was in turn followed by a policy allowing market forces to determine the most efficient use of spectrum - thus the auctions that gave rise to Advanced Wireless Services. The latest trend is for "Open Spectrum". By defining interference as a cognitive problem rather than a physical problem, Open Spectrum proponents argue that smarter devices will enable efficient, shared use of the spectrum, and what was once scarce will now be abundant. "Communication is no longer a matter of frequency, but of computation." says Kevin Kahn, director of communications technology for Intel.

Of course, regardless of the legislative philosophy that brought us here, the fact remains that the FCC's policy of "tacit allowance and benign neglect" (in the words of John Nady) towards wireless microphones have come home to roost. We are faced with the head on collision of TVBDs and wireless microphones - each attempting to share the same spectrum at the same place and at the same time, each with vastly different tolerances to interference - if you are delayed for a few seconds while you retrieve your email using your fancy white space device, no big deal - if, on the other hand, the hero's radio mic suffers a drop out of even 1 second on a live broadcast, that's a problem!

On November 4th of this year, the FCC unanimously voted to allow TVBDs to access unused TV spectrum between 54 Mhz and 698 MHz. The Economist in their November 7th issue giddily exclaimed:

How much would you pay for unlimited access to WiFi hotspots that stretched for miles instead of a few hundred feet, provided unbroken connections even deep inside buildings, and offered broadband speeds ten times faster than today’s wimpy connections found in coffee shops, hotel lobbies, airport lounges and homes?

How about nothing, or next to nothing? That could be on the cards within a couple of years, thanks to a decision taken this past week by America’s Federal Communications Commission (FCC).

By all accounts, the Report and Order makes clear that licenced Part 74 users(eg. Wireless Mic users) will take priority over TVBDs. According to the report:
One of our considerations in this matter is to ensure that channels remain available for use by wireless microphones. While we are aware that many wireless microphones are now operated, without the required license, we nonetheless understand the important function that wireless microphones serve and find that it is in the public interest to preserve spectrum in the TV bands that is available for their use.

According to the FCC R&O, TVBDs are divided into two types of devices:

  1. Fixed Devices. These "base station" devices will be allowed to transmit with up to 4 Watts EIRP of power (the same power as a UHF Motorola CP200 walkie talkie), and can transmit on any unoccupied TV channel between channels 2 and 51 - except 3,4 and 37 and any channel adjacent to a DTV station - although this last restriction may be eased pending adequate proof that it will not cause interference. In addition, fixed devices must transmit identifying information to aid in finding it in cases of interference. Fixed Devices can communicate with other Fixed Devices (for the purpose of "wireless backhaul" of data back to the internet) or with personal/portable devices described below.

  2. Personal/portable devices. These can be in the form of laptop adapter cards or handheld internet access devices. They communicate with the base station or another personal/portable WSD. They are able to transmit between TV channels 21-51 at up to 100 mW EIRP, unless they are transmitting on a channel adjacent to a DTV station, when they must reduce their power to 40 mW EIRP.

The Commission specified the following protections for wireless mics in the R&O:

  1. Spectrum Sensing. The White Space Device (WSD) must reliably detect existing RF carriers from wireless microphones and television stations, and stay off those frequencies.
  2. Geo-Location Database. The WSD uses a built in GPS receiver to determine its location and then query a database which would inform the TVBD of existing TV channels and registered locations where Part 74 devices (wireless mics) are operating. Under this plan, according to the Commission, "wireless microphone licensees will be allowed to register the sites where they operate along with the days and times when they operate. The database will then prohibit operation of TVBDs near that site on the channels and at the times used for wireless microphones". In addition, fixed TVBDs must register their location in this database. Specific transmission restrictions are imposed on the TVBDs that cannot connect to the database.
  3. Personal/Portable devices are barred from operating from TV channels 14-20, and must have a fixed antenna. (The receive antenna used with fixed devices shall be located outdoors at least 10 meters above the ground.  The antenna system shall be capable of receiving signals of protected services equally in all directions.  The transmit antenna used with fixed devices may not be more than 30 meters above the ground.) This means that Fixed Devices can only communicate with other Fixed Devices between 470-512 MHz, presumably with directional transmit antennas, thus limiting its use in that band for backhaul deployment.
  4. In the 13 Major Economic Markets (markets with T-Band), TVBDs are restricted from operating on the channels allocated for T-Band use, as well as two additional channels: The first available TV channels above and below TV Channel 37.
  5. Adaptable power control. The RF output power of TVBDs must be reduced to the absolute minimum that is required for communications.
  6. Rigorous testing and enforcement of device certification and "proof of performance" requirements, especially if a manufacturer chooses to rely only on "spectrum sensing" without the aid of a geo-location database.

In any case, TVBDs are still a ways away from being released in the wild. The technical hurdles, particularly regarding spectrum sensing are enormous, as demonstrated to FCC engineers when prototype devices were used in the real world environments of an NFL stadium and a Broadway theater this past summer using Shure and Lectrosonics wireless mics. Shure wrote in their comments about the FedEx Field demonstration::

"...the prototype devices were unable to consistently identify operating wireless microphones or distinguish occupied from unoccupied TV channels. More troubling, the devices failed to detect the presence of wireless microphones when switched on - an occurrence that takes place multiple times during any NFL game."

Google's co-founder Larry Page, by the way, called the tests "rigged", adding, "That's the kind of thing we've been up against here, and I find it despicable." Shure denied any wrongdoing, saying the tests were open to the public and, "executed based on sound engineering science and real-world operating scenarios."

In addition, multiple databases must be developed (the rules for selecting database vendors, let alone the databases themselves, have not even been published yet) and must be updated at least daily. As Lectrosonics wrote in a memo to customers, "If your wireless microphone systems are currently on channels between 470 MHz and 698 MHz, we suggest a "wait and see" approach before replacing them. You may not end up needing to replace them at all."

If you're looking to purchase new wireless systems, however, there really is no obvious choice, and it will be some time before we see TVBDs that can meet all of the FCC's requirements.

TV Converter Box Program Logo

Countdown to February 17, 2009
By now, we're all aware that at midnight on February 17, 2009, full power analog stations will cease transmission (stay tuned for the Gotham Midnight Spectrum Party!). What is not as well known is that there are stations which are exempt from the transition. Over the past few years, a number of low power TV , translator and relay stations have sprung up across the US. These stations are exempt from the February 17th shut-down deadline. Furthermore, a number of DTV stations will switch channels on February 17th, some to their original analog assignment, some to a different channel assignment, further complicating wireless mic coordination.

All of the major wireless manufactures host frequency availability information on their website - you indicate your location, and they'll tell you what tv channels are "open". To find the most accurate information, including precise transmitter locations, effective RF power, height and coverage pattern, you'll need more detailed information. Each different location that you'll be considering will have different usable TV channels depending on your proximity to the TV transmitters and their contour pattern.

I've found several websites very helpful:

Finally, here are the FCC databases themselves. Web front ends are available at:

"What's the best frequency block going to be?"
So which TV stations will be occupied as of December of 2009? After analyzing the data from the above websites, and choosing a geographical location limited to midtown Manhattan, I came up with the following Lectro/New York-centric analysis:

Block 470
T-Band Channels - According to TV channels 14,15 and 16 are used for Land Mobile Radio for both commercial and public safety entities in the New York/New England Area. Searching the ULS, we find that there are approximately 675 frequencies between 470 and 512 MHz licensed within a 5 mile radius of Gotham Sound, the majority of them between 470-488.

Thus, we can safely conclude that Block 470 is not good in New York, and if used would require  careful coordination to avoid intereference with public safety agencies.

Block 27
Contrary to early fears, Block 27 was not made entirely useless by the 700 MHz auction.

If we look at the frequency boundary of Block 27, it starts at 691.2 MHz and therefore catches the tail end of TV channel 50 and all of TV channel 51. If you own Block 27 radio mics or IFBs, you should definitely research what will be happening with those TV channels in your area - you may not need to replace them.

Unfortunately in New York, TV channel 51 is reserved for WNJN (although they are operating at reduced power due to financial difficulties), and its use may be problematic depending on how closely you're operating near their transmitter in Montclair, NJ.

Block 29
I know, I know - Block 29 is above 700 MHz - its use punishable by fates worse than death. But hang on - let's look at some of the information above one more time. We know that the FCC has merely announced their intent to make the manufacture, import, sale or use of radio mics above 700 MHz illegal - it's not actually illegal yet.

I bring up Block 29 specifically because it contains a small slice of spectrum NOT auctioned off - the infamous "Block D". Since the dates of the Block D auction haven't even been announced, you may have a little bit extra time left to use your Block 29 wireless between 758 MHz and 763 MHz.

At least until the FCC turns their intention into Federal law.

Under no circumstances should you consider buying a Block 28 or Block 29 wireless for use in the United States.

Block 944
To combat the shrinking available spectrum, some wireless microphone manufacturers produced systems in the frequency range between 944 MHz to 952 MHz. It seemed like an easy choice - it was set aside in the Commission's Part 74 rules for Low Power Broadcast auxiliary use. Unfortunately, as the Society of Broadcast Engineers notes, "it is only broadcast licensees and broadcast network entities that can use this band. Cable television operators, motion picture producers and television program producers are not eligible to use any BAS band for LPA operation except unoccupied television channels." In other words, if you or the company you work for doesn't have a licensed broadcast TV or radio transmitter, you're probably not eligible.

If you have purchased wireless mics or IFBs in this block of frequencies, you should return it to your dealer as soon as possible (unless of course you are an eligible user). As the SBE notes, "the 944-952 MHz Aural BAS band is heavily occupied in most areas of the United States.".

This leaves the following TV channels that are open or nearly open in midtown New York after the DTV transition: 17, 19, 20, 22, 23, 25, 26, 41, 42, 46,47, 49, 50

Remembering our TVBD R&O, it would seem that TV channel 26 and 42 will be left off limits to a TVBD in New York, since we are in a "T-Band" city, and they are the first "available" channels above and below TV channel 37. This assumes that all construction permits are in fact built into operation TV stations. It is also based on the strictest interpretation of what constitutes an "available" TV channel, and will certainly require clarification by the FCC. For example, the first available channel in Montvale, NJ is NOT the same first available channel in midtown Manhattan, despite the fact that both places are considered to be part of the New York market, and only 20 miles apart. In other words, which entity determines what is the first available channel in a given market- the device or the FCC?

We are therefore recommending the following blocks for use in New York, which we believe will be good well past the DTV transition and White Space Device introduction:

Block 19 - 3 empty TV channels
Block 20 - 2 empty TV channels
Block 21 - 2 empty TV channels + clear channel of TVBD (TV26) pending FCC clarification
Block 24 - 1 empty TV channel
Block 25 - 2 empty TV channels + clear channel of TVBD (TV42) pending FCC clarification
Block 26 - 3 empty TV channels

Future of Radio Mics
If you are on the "wrong" frequency, definitely consider taking up the manufacturer on their offers for rebates or reduced price frequency changes. Lectrosonics are offering the following prices to end-users to "reblock" their components:

SMA (SM) $270.00
SMDA (SMD) $270.00
SMQA (SMQ) $285.00
MM400C $285.00
UM400A (UM400) $275.00
UM450 $310.00
UH400A $375.00
UT $295.00
IFBT4 $465.00
UCR401 $345.00
UCR411A $565.00
VRM* $465.00
VRFIELD* $465.00
LMA $495.00
IFBR1a $361.00
VRS $225.00
VRT $389.00
R400A $467.00
UCR100 $357.00

*Upgrade to Wideband

As of this writing, Shure and Sennheiser have announced rebate programs for those users looking to trade-in systems on less than ideal frequency blocks.

Companies will continue to provide innovative solutions. Zaxcom's transmitters are always recording the audio onto mini-SD cards so that the wireless mic is basically transmitting a scratch track, but recording the "real" audio on mini-SD. It is ironic that the very thing that may inadvertently cause the interference (TVBDs) may be the very technology used to transport the audio from the mini-SD card to the editing room! Zaxcom's other innovation is two channel transmission, perfect for wireless hops from mixer to camera in ENG situation, so that half of the number of carriers are required compared to other wireless mics.

I'm sure we'll also see changes to the way radio mics users are licensed. I suspect that two groups will be created - the first group consisting of the Part 74 eligible groups (the eligibility of which may be expanded), and the other, a kind of "General Wireless Mic Radio Service" or GWRS which exists secondary to the Part 74 users.

This is why I feel that it's important to get a Part 74 license if you're eligible. Additionally, there is language in the White Space TV Band R&O that is ambiguous about whether those without a Part 74 license will be able to register wireless mic sites in the geo-location database. In the coming month, Gotham will be applying for our Part 74 license, and we'll document the steps required so that our customers can obtain their own.

Although the years ahead will prove very challenging for those of us that rely on radio mics, careful planning, engineering and coordination will be the keys to successfully using wireless devices.

In the coming weeks, we will add more detailed analysis of the changing spectrum, as well as information about obtaining a Part 74 licence.

With special thanks to Henry Cohen of Production Radio Rentals, Howard Kaufman and Karl Winkler of Lectrosonics, and Joe Ciaudelli of Sennheiser. 

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The Use of Wireless Mics in the U.S. Beyond the DTV Transition
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Happy Holidays from Gotham Sound!

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