The wireless landscape for pro audio users in the U.S. continues to evolve. Let’s look at the current state of the union.
We’re Kicking You Out of The Band
Way back in 2008, the FCC auctioned off a portion of the UHF band, selling it to communications companies like AT&T and Verizon for broadband use. This auction essentially forced the pro audio community in the U.S. out of the frequency range between 698 and 806 MHz (as of June 2010) — a frequency range which we had been using extensively. Some of that spectrum was set aside for new public safety channels, but most of it was designated for broadband delivery to smart phones and similar devices.
Additional multi-stage auctions in 2016 and 2017 forced pro audio out of the “600 MHz band,” which is roughly 614 to 698 MHz. Certain frequencies in the 600 MHz “guard band” (614 to 616 MHz) are still available for unlicensed use; certain frequencies in the 600 MHz “duplex gap” are still available for licensed use (653 to 657 MHz), and for unlicensed use (657 to 663 MHz). VHF and UHF frequencies ranging from roughly 54 MHz to 602 MHz are also still available for both licensed and unlicensed use. Users of unlicensed wireless microphones are also permitted to operate in frequencies outside of the TV bands: 902 to 928 MHz, 1920 to 1930 MHz, and portions of the 2.4 GHz and 5 GHz bands under certain rules such as a restricted transmission power. Licensed wireless microphone use is permitted in portions of the 900 MHz band (the frequency range from 944 to 952 MHz is for reserved licensed use by radio and TV stations for studio-to-transmitter links) as well as 1,435 to 1,525 MHz and 6,875 to 7,125 MHz. See below for more about licensing.
None of this has changed, and while you might be able to use some of the “forbidden” frequencies without getting a cease-and-desist notice from AT&T, you’ll probably encounter so much interference that your wireless mic won’t work properly. Note that when we say “wireless microphones” we’re also referring to wireless instrument, IEM, IFB and intercom systems.
Manufacturers of wireless equipment are no longer allowed to sell in the U.S. systems that operate in the bands now owned by the broadband providers. This does not, however, prevent people who own older, obsolete systems from selling them on the used market. So, if you’re in the hunt to purchase wireless gear second-hand, find out the operating range or you could end up purchasing a pile of RF paperweights.
2.4 GHz is Still the Wild West
Fallout from the aforementioned FCC auctions spurred the popularity of wireless systems that operate in the 2.4 GHz range (technically 2.4 to 2,483.5 MHz). In general, 2.4 GHz wireless instruments are legal for unlicensed use in just about every country. They don’t require much in the way of frequency coordination, often providing a switch that simply toggles between a half-dozen or so possible channels, or auto-selecting an unused channel. The big problem with the 2.4 GHz band is that it’s a crowded band where a lot of Wi-Fi devices live, including cell phones and Bluetooth devices. As a result, tablets, Wi-Fi routers, and smartphones that employ Wi-Fi calling are all potential sources of interference for wireless mics and instrument systems operating in this band. And — while 2.4 GHz wireless devices may operate without trouble during soundcheck when a venue is empty, the increase in RF activity once the venue fills with people (and their smart phones and BT ear buds) may render your wireless system useless.
There are some wireless systems that operate in the 5 GHz band or as “dual-band” devices (for example the Shure GLXD4+ in Fig. 1), which can manually or automatically switch between the 2.4 GHz and 5.8 GHz ranges. As of now, the 5 GHz band is working out pretty well, because it’s less crowded.
VHF Might Not Be Such a Bad Idea
When UHF wireless instruments became affordable, VHF was ousted to the isle of misfit toys, labeled as being inferior technology, and UHF became the de facto standard. VHF lives in two ranges: low-band VHF and high-band VHF. Low-band VHF ranges from around 49 to 108 MHz (in the U.S.), where there’s a lot of activity including TV channels 2 through 6, FM radio, walkie-talkies, radio-controlled toys, and some cordless phones — so it’s not a great place for a wireless guitar system to live. Antenna length can also be an issue because a ¼-wavelength antenna (the accepted length for efficient transmission) can be three feet long(!).
High-band VHF ranges from roughly 174 to 216 MHz (in the U.S.), and though this is less crowded than low-band VHF, there’s still a fair amount of activity including TV channels 7 through 13 and some aircraft communications. There’s a small band from 169 to 172 MHz known as “traveling frequencies” that are open for unlicensed wireless microphone operation across the U.S. So, if you’re on a tour that only needs one or two microphones (stand-up comedy, for example), high-band VHF could be a viable solution. VHF has a longer line-of-sight distance range, which also means it can be subject to more interference from outside transmissions, generally has a longer battery life than UHF, and is cheaper to produce, thus resulting in lower retail prices.
WMAS is a Reality
Approximately a year ago, the FCC adopted new rules permitting operation of WMAS or Wireless Multichannel Audio System here in the U.S. WMAS is an advanced wireless technology designed for pro applications that allows an increased number of devices (microphones, instruments, IEMs) to operate within available spectrum (see “On the Digital Edge” in the October 2023 issue of FOH for more info). WMAS systems are expected to be available this year including the Shure Axient Digital PSM and Sennheiser Spectera. Axient Digital PSM is an IEM system supporting up to 28 channels in a 6 MHz band (U.S.) and up to 40 channels in an 8 MHz band (Europe). Spectera (see Fig. 2) features a base station capable of bidirectional transmission of up to 64 channels (32 in/32 out) using up to two wideband RF carriers (6 MHz in the U.S.; 8 MHz in Europe). Prices aren’t for the faint of heart, but both systems deliver advanced technology with high channel counts, providing a huge advantage for large-scale events.
Do You Have a License for that Monkey?
The FCC allows certain organizations to obtain a license to operate wireless microphones in the RF bands identified in their licenses. Qualifying entities include AM, FM and TV stations, cable TV systems, broadcast networks, venue owners, and sound vendors that often run more than 50 wireless devices for large-scale events like theater productions, sporting events or concerts. If you’re running a few channels of wireless mics, guitars and IEMs at the local club, you don’t need to get a license, but you do need to comply with some basic rules that include not exceeding 50 milliwatts output power when operating in a TV band, and not exceeding 20 milliwatts when operating in the 600 MHz guard band or duplex gap. This shouldn’t be a problem for most pro audio users, because few wireless systems max out at a transmission level of 50 mW (20 mW is more common), and many offer the option of transmitting at a reduced level such as 10 or 20 mW. Tip: Operating at the maximum output level is not always the best course of action, because running multiple systems at reduced output can actually decrease the amount of local RF “pollution” and improve performance for all of the systems onstage.
Steve “Woody” La Cerra is the tour manager and front of house engineer for Blue Öyster Cult.
