The Search for Spectrum: Wireless Systems in the VHF Band
Anyone who has used wireless audio systems in the past twenty years is aware of the ever-changing landscape in the RF spectrum. In 1997, the Federal Communication Commission (FCC), which regulates the use of radio frequencies in the US, began planning a reallocation of the broadcast spectrum to make room for the DTV transition. That resulted in the June 2010 closing of the UHF 700 MHz band for wireless audio system use.
With the UHF 700 MHz band exclusively reallocated to public safety agencies and licensed wireless service providers, audio manufacturers scrambled to retool. Wireless audio customers were left with gear that had to be replaced. The audio industry was awash in trade-ins and rebates.
Two years later, in 2012, the explosive growth of mobile data prompted Congress to authorize the FCC to conduct an Incentive Auction in which broadcasters could voluntarily trade spectrum licenses for a share of auction proceeds from successful bidders. The Incentive Auction commenced in the first quarter of 2016 and is ongoing. It will very likely result in the eviction of wireless audio users from some or all of the 600 MHz UHF TV Band. The pro audio industry has responded proactively with new wireless systems and solutions capable of providing dependable wireless performance in other parts of the RF spectrum.
The RF Spectrum: UHF vs VHF
The basic components of a wireless system—transmitter (either a bodypack or a handheld mic) and receiver—are identical regardless of the frequency band in which they operate. One important difference is the RF range in which they are engineered to function: UHF or VHF.
The VHF (Very High Frequency) band runs from 49 MHz to 216 MHz. Beginning at 300 MHz and extending to 3 GHz is the UHF (Ultra High Frequency) band.
Wireless UHF systems have dominated the industry in recent years. The available UHF spectrum is eight times greater than the available VHF spectrum, so there are more UHF frequencies to choose from. That means the UHF band is better suited for applications where multiple systems are in simultaneous use. Wavelengths are shorter, and the antennas are smaller. UHF systems, once the more expensive choice because their feature sets were more robust than VHF system features, nowadays offer a wide range of models and prices.
While the UHF television band continues to face reallocation threats, it remains the largest contiguous block of radio spectrum in most countries, particularly in the US. For that reason, it is expected to remain the primary range for professional wireless audio use.
According to Shure Associate Director of Technical Support and Training Gino Sigismondi, "the combination of a larger frequency range, smaller antennas and more advanced feature sets in UHF systems resulted in the near-obsolescence of professional VHF wireless microphone systems." Shure, for example, ceased production of wireless VHF systems in 2004.
VHF systems, however, have a specific advantage - longer wavelengths travel farther and may be more efficient at transmitting through air, walls and human bodies.
With the Incentive Auction likely to cause a further reduction in UHF spectrum, manufacturers, including Shure, have reconsidered the usefulness of the VHF band. The good news for users, according to Gino, is that "dramatic radio circuitry advances have fueled the development of VHF systems that incorporate features like wide tuning range and greater spectral efficiency that were previously available only on UHF systems." These are not the VHF systems of yesteryear.
Multiple Wireless Product Solutions
The search for usable spectrum has resulted in new wireless systems that operate in the VHF band, 900 MHz band, 2.4 GHz band, and in the DECT (1920–1930 MHz) range. Each range has specific characteristics. In an increasingly crowded field, according to Gino, "Any spectrum (legal of course) is good spectrum."
In April 2016, Shure announced new VHF versions of two digital wireless systems, ULX-D® and QLX-D®. These new VHF systems match their UHF counterparts feature for feature, offering high-quality sound, 42 MHz of predictable tuning bandwidth, networking capabilities, and a full range of antenna accessories for optimized RF coverage. It's one more way that audio manufacturers are answering the call for additional wireless options as we all face uncertainties in future wireless spectrum availability.
It's hard to predict with any certainty exactly what will happen with the Incentive Auction. The best advice comes from wireless audio lobbyist and Vice President of Corporate & Government Relations Mark Brunner at Shure. He encourages wireless audio users to stay current with regulatory changes that may impact open channels in the RF spectrum. "Education and awareness will lead people to product choices that are affordable, appropriate for their needs and optimized for the environment in which they're operating," Mark advises.
Something else to keep in mind: There will be a 39-month transition period which begins once the repacking plan for the UHF TV band is announced, so the real impact to wireless users likely won't occur before 2020. Throughout the process, Shure will continue to serve as an industry advocate, information resource and product innovator. We'll be posting updates here on the Shure Blog, the Incentive Auction Resource Center, and announcing them on Facebook, Twitter and LinkedIn. Be sure you're following us so you can stay informed.