For the last 22 months, wireless microphones haven’t been allowed to operate in the 700 MHz band (698 – 806 MHz) in the US. Many systems were sold in this spectrum, but are now illegal to resell or operate in the US. This remains news to some wireless users, and illegal 700-band systems can be found in ballrooms, churches and schools, with some continuing to plead ignorance as an excuse.
Though it’s possible to operate some 700-band equipment because some frequencies are currently unoccupied, there’s increased likelihood the 4G LTE companies (Verizon and AT&T), which spent billions to buy this spectrum, will start using it soon, if they’re not already. In Florida, Verizon’s LTE is available in 14 cities, while AT&T’s is only working in two, but both companies expect to finish rolling out next year. When interference from new services does occur, it will squash wireless mic signals like bugs.
Just as importantly, operating a wireless mics or IEMs in a 700 MHz public safety band could interfere with an emergency responder’s radio reception should they be in a weak signal area (such as inside a venue), creating life-safety issues. Furthermore, operating wireless equipment in the 700-band is punishable by fines on the order of $10,000. Hardly worth it.
Scofflaws continue to operate 700-band wireless, confident that the FCC does little to police it and ignorant about wireless mics effect on new services. In a recent incident in Washington State, Verizon threatened to notify the FCC of a church’s illegal wireless equipment. As U.S. LTE services continue to roll out, 700-band operators will act to protect their investment. Yes, this is about iPhones. BTW, check out Spectrum Bridge’s iPhone Apps: “ShowMyWhiteSpace” (free), or “micFrequency” ($5), which both display similar location-based information based on the official database.
In its September 2010 Second Report and Order, the FCC acknowledged two classes of wireless microphone operators, “licensed” and “unlicensed.” It’s estimated that for every licensed wireless microphone, there are thousands of unlicensed ones. Licensed operators enjoy better protection from TV Band Devices (TVBDs) and are permitted up to 250-milliwatt (mW) transmissions in UHF spectrum instead of being restricted to 50 mW.
The first official but limited operation of TVBDs is a tower-based municipal wireless network in Wilmington, NC in partnership with Spectrum Bridge where the applications include traffic cameras, Wi-Fi access in city parks and surveillance of wetland areas begun in January.
Even after TVBDs begin widespread operations, wireless mics may be operated, with or without license, on any TV channel (except 37, reserved for radio astronomy) that’s not assigned for TV or Public Safety broadcast. Your only benefit from buying and operating equipment in a “reserved channel” safe haven is that when (and if, some say) the change comes, you’ll have already incorporated the new best practices.
The concern is for a future when TVBDs will operate in the same unused UHF TV broadcast spectrum “white space” as wireless mics, other than the FCC-designated wireless mic “reserved channels.” The FCC exclusively reserves the first unoccupied TV channel above and below TV 37 for wireless mic users. However, it is often different TV channels from one city to the next, particularly in the largest cities.
For example, in Los Angeles, the first open TV channel is TV 30. In Manhattan, TV channels 22 and 42 are reserved channels for wireless mics, nowhere near TV 37. In Dallas, TV 33 and 47 are reserved; in Houston, it’s TV 33 and 49; and for San Francisco, it’s TV 32 and 48. Bottom line: in the biggest U.S. cities, consult with an RF expert. In many smaller cities and towns, the reserved channel will be TV 35 or 36 and TV 38 or 39.
Two more TVBD restrictions keep additional future UHF spectrum open for unlicensed users. High-power (4W) tower-based TVBDs may not operate in a channel next to a broadcast TV station. Lower-powered (100mW) portable TVBDs are not allowed to operate below TV 21 (below 512 MHz). Therefore, in many cities, the spectrum between 470 and 512 MHz, called the UHF “T-band,” continues to be a good place to operate wireless microphones as long as it is in the unoccupied TV channel next to a DTV broadcast.
That said, in major metropolitan areas, public safety radio systems are also operated in the UHF T-band, and wireless mics are prohibited in those channels. The following U.S. cities employ these TV channels for public safety: Boston (14, 16); Chicago (14, 15); Cleveland (14, 15); Dallas (16); Detroit (15, 16); Houston (17); Los Angeles (14, 16, 20); New York (14, 15, 16); Miami (14); Philadelphia (19, 20); Pittsburgh (14, 18); San Francisco (16, 17) and Washington, D.C. (17, 18). In most cities, there are likely one or more secondary wireless mic safe havens between 470 and 512 MHz that will be free of TVBD interference.
During the DTV spectrum re-allotment, many users took perfectly good 700-band equipment out of service and replaced it with new systems operating on lower frequencies. However, unless new equipment operates near TV 37 or below TV 21, there’s no guarantee it will continue to operate interference-free after TVBDs come into widespread service, as outside of these safe havens, TVBDs enjoy the same unlicensed secondary user rights.
Many manufacturers are aware of this situation, however it’s up to vendors and end-users to pay attention when buying new wireless equipment to make sure it has a frequency group that is future proof. Our sidebar has a partial listing of groups that operate adjacent to TV 37 in a wireless mic reserved channel or below TV 21 in a T-band safe haven.
To be clear, until TVBDs are in widespread use in a few years, equipment outside this very specific spectrum will work perfectly fine. There are even some who claim that because it is impossible for TVBDs to operate in New York or Los Angeles that these TVBDs won’t come to pass. Hard to predict the future.
Signals from these new broadband TVBDs will be digital modulation spread across most of a 6 MHz TV channel. The amount of power allowed is 100 mW for portable devices, but only 40 mW when operating in a channel next to an occupied TV channel, so these signals may appear as low-level noise in the spectrum and when protected by the shielding of indoor venues may not even be a factor until upscale audiences with pockets full of TVBDs fill the VIP seats in the front row (or pick up their guitars and play).
Given the recent bill in Congress authorizing the FCC to further consolidate UHF spectrum in years to come, careful consideration of frequencies for new wireless equipment are key to maximizing the useful life of new systems. Even though TV channels 40 to 51 (626-698 MHz) are the clearest spectrum at the moment, I predict that eventually the day will come when it too will be auctioned off, though not likely for 10 years.
There are several alternatives to using unoccupied UHF TV white spaces. One is to simply go back to VHF wireless mics, however, most VHF systems aren’t frequency-agile. There are eight VHF “Traveling Frequencies” at 169-172 MHz, just below TV channel 7, but it’s impossible to operate more than a few systems in this range. Above that, VHF can be used in the Upper VHF (174-216 MHz) not all occupied by TV channels 7 to 13, but it varies by city.
In North and South America the 902-928 MHz ISM band is an option for unlicensed digital wireless, though it is congested in some areas. Several manufacturers offer digital wireless mics that operate license free worldwide in the 2.4 GHz “WiFi” band, though that spectrum is widely congested. There are also new digital systems that operate in the 6 GHz band. The future of UHF wireless is likely also digital, since it can provide higher spectrum density and there can be twice as many digital as analog systems operating in the same 6 MHz UHF TV channel.
If you’re thinking of adding wireless mics to your inventory for the coming season, I can recommend the following frequency groups for the following makes and models to be generally good for unlicensed use as TVBDs become widespread in a couple years. That said, in the largest cities, the exclusive “reserved channel” safe havens for wireless mics may be located pretty far away from TV 37, so in places like Los Angeles, New York, Dallas, Houston or Philadelphia, consulting with an expert is recommended.
Unlicensed Wireless Mic Frequency Groups Near TV 37 (608-614 MHz) or below TV 21 (512 MHz)
Sennheiser
XSW: B (614-638 MHz)
ew 100: G (566-608 MHz)
ew 300: G (566-608 MHz)
ew 500: G (566-608 MHz)
2000 Series: Gx (558-626 MHz)
Shure
UHF-R: G1 (470-512 MHz)
and J5 (578-638 MHz)
ULX: G3 (470-506 MHz)
ULX-D: G50 (470-554 MHz)
and J50 (572-636 MHz)
SLX: G4 (470-494 MHz)
and G5 (494-518 MHz)
Audio-Technica
2000 Series: I (482-507 MHz)
3000 Series: I (482-507 MHz)
AKG
DMS 700: Band 1 (548-698 MHz);
WMS 470: Band 9 (600-630 MHz)
beyerdynamic
S600: Mid Band (506-530 MHz)
S910: Low Band (482-518 MHz)
and Mid Band (590-626 MHz)
Audix
RAD-360: Purple (614-626 MHz)
Lectrosonics
Block 23 (588.8-614.3 MHz)
Block 24 (614.4-639.9 MHz)
Block 470 (470.1-495.6 MHz)
Block 19 (486.4-511.9 MHz)
Sony DWS
Group 30 (566-638 MHz)
