In the market for a new wireless audio system? If so, you’re probably aware that some types of microphones are better choices than others because of upcoming changes to the spectrum. We put together a list of things you can do, and certain types of mics you can buy, in order to minimize risks.

First, let’s clarify what we mean by “future-proof.”

We do not mean that if you follow these guidelines you will never have to purchase another system again. We cannot promise that this guide will weather unforeseeable changes in technology or government policy in the future that no one can predict.

We mean "future-proof" in the sense that Wikipedia has it: developing methods or strategies to minimize "the effects of shocks and stresses of future events." (High five, Wikipedia)

Be aware of the timeline.

In early 2016, the FCC plans to hold an “Incentive Auction” to clear some, all, or more than the 600-698 MHz band. (A discussion of what the Incentive Auction is and how it works is outside the scope of this article.) Unlike in the 700 MHz auction which many pros remember from 2008, wireless microphones will not be evicted immediately. They will have up to 39 months to vacate whatever spectrum is auctioned off. Since the auctions are not even scheduled to begin until next year, if one were to purchase a microphone in the 600 MHz band today, he/she will likely be able to legally operate it for the next 3-5 years. There is also the possibility that the auction will fail, or that the repacking of broadcast TV stations will take longer than expected, extending legal operability well beyond 5 years.

For many, 3-5 years is enough time to realize benefits from an investment, and would coincide with typical system lifespan in some high use applications anyhow.

Buy in the UHF "safe zone."

If you prefer UHF and want to be on the safe side, it’s best to purchase a system that operates below 600 MHz. There is a lower probability that those frequencies will be sold. We don’t know exactly how much spectrum will be sold. There are a number of scenarios. As little as 42 MHz, as much as 144 MHz, or something in between.

But we do know the worst case scenario: everything 554 MHz and above going away. If you want to be on the really, really, safe side, purchase a block/band between 470-548 MHz. This will almost certainly be available after the incentive auctions are complete and well into the future. (Caveat: the spectrum may be available, but not useful. See "unknowns" at bottom of post for more.)

AKG Band 7

Audio Technica I

Lectrosonics Block 470

Lectrosonics Block 19

Lectrosonics Block 20

Sennheiser A1

Sennheiser A2

Sennheiser A3

Shure Band H8

Shure Band G4

Shure Band G5

Shure Band H5

Shure Band G1

Shure Band G50

The FCC would like to auction the T-band (470-512 MHz) around 2020. That is some time away, and the fate of remaining wireless microphones there is unclear. The FCC seems to want to allow TVBDs to operate in T-band spectrum, so that bodes well for microphones and we can expect to have those 42 MHz for the foreseeable future.

Need just one or two channels? Consider ISM bands.

ISM band microphones are a good choice for small venues that only require one or two channels and have low to moderate WiFi activity in their facilities. ISM bands are internationally standardized unlicensed bands that are not going away. There are a few of them, with 2.4 GHz being by far the most popular. Most mid grade digital wireless mics hitting the shelves these days seem to be 2.4 GHz. 900 MHz is also an option, as well as 5.8 GHz, which has inferior propagation characteristics but may become viable as antenna technology improves and other bands grow more crowded.

There are both pros and cons to bconsider when shopping for 2.4 GHz microphones, which we wrote about in this article. 2.4 GHz microphones work well as long as there are few WiFi devices and the channel count is kept low.

Use external antennas and antenna distribution to maximize available spectrum.

Using and correctly placing external antennas is the single most powerful way to increase channel count and ensure reliable operation. Directional antennas increase range and reduce off-axis interference when used correctly. More involved remote and distributed antenna systems using either long coaxial cable runs or fiber optics even allow frequencies to be reused in the same facility. Routing multiple channels through antenna combiners and distributors reduces intermodulation artifacts along with other benefits. Finally, external filters like notch and tuned cavity filters may become increasingly necessary. Right now they are used only by the most advanced users.

Need a lot of channels? Get a Part 74 license, and go digital.

The Incentive Auctions will be most inconvenient for organizations using large systems. They may have tens of thousands of dollars in inventory which they need (not want) to know will still be useable in the near future.

If you routinely operate more than 50 channels of wireless (including comms, in-ears, and IFBs), you are now eligible to apply for a Part 74 license. A Part 74 license gives you two important things: the privilege of using 250mW transmitters, and registration on the White Space Database which entitles you to interference protection from TVBDs (more on TVBDs below). Previously, only film and broadcast professionals could hold Part 74 licenses. In a gesture of good faith, the FCC has broadened eligibility criteria to include most large scale wireless audio users.

If you use more than 50 devices and want to continue doing so after the auctions, it is important to get yourself or your organization licensed as soon as possible. For additional details on pursuing licensure, please contact me at the email address below this article and I will gladly put you in touch with the right resources.

Transitioning to digitally modulated wireless is also another effective way to maximize available spectrum. Digital microphones are less susceptible to intermodulation artifacts than analog frequency modulated (FM) models, so you can fit a larger number of digital mics into the same span. Digital models are more likely to incorporate intelligent radio protocols that sense ambient spectrum and communicate between transmitters to self-coordinate in real time. Some systems may transmit analog FM but use digital technology to self-coordinate, like if you use a Shure Axient system with UHF-R.

A few unknowns...

TVBDs: TVBDs are a new class of device authorized to operate on UHF spectrum. We discuss TVBDs at length here. As of today there aren’t many of them, and those that do exist are limited to rural areas. It is possible that TVBDs will become numerous. Since they transmit on the same frequencies as wireless mics, and are not required to sense other types of low power radios, they pose a significant interference threat to nearby unlicensed wireless microphones. The only way to protect against them is to operate somewhere they are not, or hold a Part 74 license.

We don’t know if TVBDs will ever make it to non-rural markets. But if they do, it’s not going to be good.

Density of repacking: Not all TV stations in the 600 MHz band are going out of business. Some of them will probably choose to remain on the air. They get to keep their broadcast rights and coverage area (give or take), but will be moved down to lower frequencies. The FCC gives additional incentive to stations who choose to move to VHF frequencies, though no station will be required to do so. Since we don’t know how many broadcasters will participate in the auction, or how many of those who do not participate will choose VHF, we don’t know how crowded the remaining UHF spectrum will be post auction.

Frustrating, I know.

A silver lining is the FCC has floated the possibility of allowing wireless microphones inside the legal contours of TV stations. TV contours are what you are checking on when you use a tool like Shure’s frequency finder. Instead, they hint that wireless microphones may legally operate wherever TV signal is beneath a certain amplitude. Technically, it’s best to have a noise floor that is as low as possible, but practically this change (if it happens) will open up many more legal frequencies even if the repacking is dense.

Leading image courtesy Daniel Dione.