Wireless Coordination
Well the time has finally arrived… Your 600MHz wireless devices are about to be illegal. Oh, and your 500 MHz devices... They’re about to have some major challenges as well! And it’s all going to happen sooner than you think. Before I get into anything too technical let's begin with a short history lesson.
Wireless microphones have traditionally been able to operate in empty channels, called “White Space”; between over the air “O.T.A.” broadcast TV stations. For instance, if there was a TV broadcast channel 20 (506 MHz to 512 MHz) and 22 (518 MHz to 524 MHz) in your local market, then you could use channel 21 (512 MHz to 518 MHz) for your wireless equipment. O.T.A. stations are allotted a 6 MHz chunk
of spectrum. This means an empty channel could accommodate a number of wireless devices. There was a time in the UHF spectrum that we had white space options from 470 MHz to 806 MHz. Then, about 10 years ago, the FCC had all broadcasters move to digital O.T.A. broadcasts thus allowing them to auction off the 698-806 MHz portion. Wireless microphone users had to abandon these frequencies and purchase new wireless equipment. Not only was there less spectrum to utilize, but all the broadcasters in the 700 MHz band were moved down to lower channels thus leaving us less white space then there was before. Well here we are again…
On March 29, 2016, the FCC commenced the “incentive auction” designed to repurpose most of the 600 MHz to 700 MHz band (band 71) for use by new licensees. This made valuable “low band” airwaves available for wireless broadband use (think cell phones). Bidding in the auction closed on March 30, 2017, repurposing 84 megahertz of spectrum. The auction yielded $19.8 billion in revenue. Approximately $13 billion was used to pay broadcasters to give up their current channels and the remaining $7 billion went to the government. I’m sure this was used for processing fees…
On April 13, 2017 the FCC released a public notice formally closing the auction and beginning the 39-month period, during which time some TV stations, and unlicensed wireless users (most wireless microphone users) will need to transition to new channel assignments. The deadline is July 13, 2020.
So what does this mean for us? Here’s the short answer… For the most part, any wireless microphone, IEM or intercom system that operate between 614 MHz to 698 MHz need to move to new frequencies. Unfortunately, that typically means purchasing a new wireless system. Additionally, it must be done within 39 months of April 13, 2017. Sort of…
Enter T-Mobile. In an effort to dramatically expand their Extended Range LTE network, T-Mobile spent around $8 billion in the Broadcast Incentive Auction to open up a large amount of the 600 MHz spectrum for their cellular services. Like any of us who have spent $8 billion on something new, we are typically very eager to start using it! T-Mobile is no exception.
The relocation of 935 US and 62 Canadian TV stations, also known as repacking, is organized into 10 phases. Phase 1 is set to begin September 14, 2018 and end November 30, 2018 with each subsequent phase starting immediately following the previous phase. So phase 2 will start on December 1st… In some markets, like Boston, the stations will be moved over several phases. Other markets, like here in Lubbock, it will all happen in a single phase. Which just happens to be phase 1! Also, like I mentioned before, T-Mobile is chomping at the bit to get things moving and has even offered financial incentives to broadcasters in certain markets to move early.
Below is a graph showing the FCC’s repacking schedule.
***Side Note***There are some great websites like SpectrumGateway.com and RabbitEars.info that have the phases laid out in spreadsheets and overlaid on US maps. They show what stations are moving and when it’s scheduled to happen. Of course, this assumes T-Mobile hasn’t already worked out a deal with those stations to move early.
What does this all mean? First, if you haven’t already, stop using your 600 MHz equipment. Not only will they become unreliable with regard to interference, but continued use could be costly. Here’s what the FCC has to say,
“Licensed and unlicensed wireless audio equipment operators must vacate frequency spectrum in the 600 MHz band as soon as any of the new licensees who acquired bandwidth in the 2017 Incentive Auction announce an intention to begin using it, whether for testing or full-time services. The FCC may impose a fine of "$10,000 per violation or per day of a continuing violation and $75,000 per any single act or failure to act" on anyone who continues to operate in the relevant spectrum.”
Ouch… Needless to say, they do not want people using these frequencies without permission. Also, an important take away is that new licensees need only announce their intention to test/use the new spectrum. Once that’s happened, you are subject to the fines listed above. With the first phase set to begin in about a month, combined with T-Mobiles aggressive time line, I would consider the 600 MHz band off limits sooner then later.
I should mention that there are a few portions (very small portions) of the repurposed 600 MHz spectrum where wireless microphones can operate. They are, however, subject to additional rules and restrictions. In addition, they may be prone to interference from the mobile downlink band. I’ll cover this in more detail later.
What does this leave us? Well that’s a complicated question as it depends on your market but here’s a simplified explanation.
470 MHz to 608 MHz –
This range of frequencies will operate much like before. The only real change will be the addition of all those repacked O.T.A. stations. As part of the auction, stations in the 600 MHz band are being moved to lower channels. As part of this, there will also be a reorganization of existing stations. For example, if a station on channel 42 (638 – 644) needs to be relocated, then the FCC may need to move a few stations between channels 14 and 36 to make room. So, there may be a lot of changes in your local market.
How does this affect you? Your wireless microphone on 501.250 MHz (Ch 19) which is
currently free from interference may need to be tuned to a new frequency if a station from the 600 MHz band gets moved there. Also, if the local station currently broadcasting on channel 26 (542-548) gets moved to channel 19 (500-506) you will have the same problem. Now you may think, “If channel 26 gets moved to channel 19 then I can simply move my microphone to 26”… Unfortunately, there’s a good chance the reason the station moved from 26 to 19 is to open room for another station to move down from the 600 MHz band.
This brings me to my next point. The 470-608 MHz spectrum is about to get crowded. Really
crowded! Below is a chart showing the 470-608 MHz band before repacking and after repacking (In the Lubbock market).
The green cells represent available white space. As you can see there won’t be much left after the repacking! Now some of these stations may be far enough away or may broadcast at a low enough power that you can still use them for you wireless systems. There are, however, very strict rules governing this. Previously, wireless microphones were only permitted to operate on a TV channel with a minimum separation distance of 100 kilometers (approximately 70 miles) between the wireless microphones and the TV broadcast antenna. Now, wireless microphones can operate 4 kilometers outside the actual service contour of a TV station, regardless of the location of the TV antenna. Licensed wireless microphone professionals are permitted to operate closer, or even within the service contour if they are indoors, and the TV signal measures less than -84 dBm. This requires and license (There are several options; Part 74 or Part 90) and a fair amount of knowledge and experience.
Finally, there are white space devices… According to Joe Ciaudelli from Sennheiser, “In 2010, the FCC established rules for White Space Devices (“WSDs”) – formerly known as TV White Space (“TVWS”) or TV Band Devices (“TVBD”) – which are unlicensed equipment also operating on unused TV channels, like wireless microphones do. W.S.D. deployment thus far has been slow, but is expected to accelerate. The audio community has been concerned about this issue because of the increased potential for interference caused by more devices using the same frequency range. However, licensed operation (part 74 or part 90) of wireless microphones takes precedence over unlicensed devices, including WSDs. White space devices use location sensing in conjunction with a channel assignment database. This database includes a list of channels reserved for wireless microphones used in registered events at protected areas, such as entertainment and sporting venues. WSDs must first access the database to obtain a list of permitted channels in the area before operating. A WSD lacking this capability can operate only under the direct control of another WSD that can access the database.” This means your wireless microphone could work great today and be unusable tomorrow do to interference caused by a white space device. If you are conducting a large-scale event you can also apply for a reservation. This will temporarily block WSDs from using those frequencies in your area.
Obtaining a Part 74 or Part 90 license from the FCC is highly recommended. However, there are a number of requirements that determine eligibility and not everyone will qualify. For instance, to apply for a Part 74 license you must routinely use 50 channels or more of wireless systems. Due to its complexity I’m not going to get into any additional details about licensing here but I highly recommend you check out the FCC’s website for more information.
614 MHz to 620 MHz –
When reorganizing this band, the FCC left some frequencies open as a buffer. They are called the “Guard Band” and “Duplex Gap”. These are unused frequencies designed to act as a spacer or buffer between various sections of the 600 MHz band. These frequencies include:
-614-616 MHz (unlicensed) Guard Band
-653-657 MHz (licensed) Duplex Gap
-657-663 MHz (unlicensed) Duplex Gap
Power output is limited to 20 mW and unlicensed wireless microphones operating in the guard band and the duplex gap will need to register with a database administrator. The administrator may assess a fee for such registrations, although that procedure has not been specified. Other than the 4 MHz within the duplex gap that is reserved for licensed users, wireless microphone operations in the other portion of the duplex gap and the lower guard band will be considered unlicensed. Given that the guard band and duplex gap are buffers to control interference between adjacent services, there may be high, out-of-band emissions (i.e., noise) from those services. Therefore, the possibility of interference to wireless microphones operating in these bands may be high, especially considering the low 20 mW microphone power limit. In comparison, permitted output power for wireless microphones in UHF TV white space channels is 50 mW and 250 mW for unlicensed and licensed operation, respectively.
So, lets sum this all up…
If you have a wireless system that currently operates above 614 MHz you should stop using it very soon. You may use it in the buffer frequencies listed above but I would NOT recommend attempting this unless you are a highly skilled wireless operator. Best advice, buy new wireless systems. If you cannot afford new wireless systems, use some wired microphones or IEMs wherever possible until you can afford new wireless.
If you have a system that operates in the 470 MHz to 608 MHz. You may continue using these devices but be aware of several things:
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1. You will probably need to retune your existing wireless microphones once the FCC repacking is complete in your market. In Lubbock, before the end of 2018.
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2. Be aware of WSDs and have a backup plan. If you do not have a Part 74 or Part 90 license and have not applied for an event reservation, you are vulnerable to WSDs in you venue. Without warning, a WSD could start operating on the same frequency as one of your wireless systems. I would have a spare wired or wireless microphone ready. If it interferes with your in ear monitors you’ll want to have a backup for that too.
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3. Hire someone who can come to your venue and provide you with RF coordination for all of you wireless systems. Our increased dependence on wireless systems coupled with the new RF environment, means our wireless system cannot be just an afterthought.
Finally, the FCC and wireless manufactures have been exploring new frequency bands for wireless audio equipment. This is beyond the scope of this paper but could offer us some alternatives in the future. These include 169-172 MHz, 944-952 MHz, 1435-1525 MHz (1.4 GHz), 6875-6900 MHz and 7100-7125 MHz. These new bands all have pros and cons. Some require licenses, and some do not. If you are in the market for new wireless equipment, you may consider one of these new bands. The 169 to 172 MHz band is getting a lot of attention in the live event market.
The topic of RF coordination and the FCC is very complex. This article condenses several hundred pages of information into something far more manageable and practical. If you have any questions or would like an RF consultation, please don’t hesitate to contact me!
Jeremiah Denning
AGD Audio Services, LLC
(360) 708-4902
Jdenning@AGDAudio.com
AGD Audio Services, LLC
Lubbock, Tx
Jdenning@agdaudio.com
