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Guide to Wireless Microphone Operation

Post FCC 600 MHz Incentive Auction

Read our guide to wireless microphone operation in the US.

Almost every venue and person using multiple wireless microphones in the United States will need to reconfigure their systems before July 13, 2020, or sooner in most areas, to comply with new federal regulations and avoid interference. Since the definition of wireless microphones includes in-ear monitors, intercom systems, and interruptible fold back (“IFB”) systems, more devices will be impacted by the new federal regulations than most people realize.

Most wireless microphones, especially those of professional grade, transmit in locally-vacant TV channels, commonly referred to as white space channels, primarily in the Ultra High Frequency (“UHF”) range. Legislation required the Federal Communications Commission (“FCC” or the “Commission”) to conduct an “incentive auction” to repurpose a large portion of UHF TV band spectrum for mobile broadband. The auction impacts the 600 Megahertz (“MHz”) band, specifically 614-698 MHz. For wireless microphone operators, this means that many UHF TV channels used today will not be available in the future.

FCC decisions concerning the incentive auction and the subsequent repacking of the TV band will significantly impact wireless microphones. Wireless microphone owners and operators should prepare for changes, including:

  • 614-698 MHz will be repurposed, and will largely become unavailable to wireless microphones after a transition period that will end on July 13, 2020.

  • There will be portions of the repurposed spectrum (e.g., the guard band and duplex gap) where wireless microphones will be allowed to operate, but under different rules (see below) including a 20 mW output power limit.

  • Some TV stations currently broadcasting on channels in the 600 MHz band will be moved to lower TV channels, thereby increasing congestion in the remaining TV spectrum. This will further reduce the number of channels available to wireless microphones in the lower UHF and the VHF bands. However, the FCC’s adoption of Sennheiser’s proposal for co-channel operations (explained below) makes previously prohibited channels now available to wireless microphones.

  • About half of existing UHF wireless microphone equipment will likely be rendered obsolete, or will require modification. Basically, no later than July 13, 2020, any wireless microphone that can tune above 614 MHz will need to be taken out of service or modified to comply with the new band plan and FCC rules. More specifically, these rules apply to any wireless microphone that can tune to any frequencies within the broadband downlink block (617-652 MHz) or the uplink block (663-698 MHz), and all existing wireless microphones with output power greater than 20 mW that will be used in the guard band and duplex gap.

  • Timing of the deployment of the new broadband services will vary by market area. Deployment in most areas is expected to occur well before 2020. A 600 MHz licensee is required to register use of its spectrum in the white space database system once it commences service in an area. Wireless microphone operators should check the database system, using the web portal of any of the FCC approved administrators (e.g., Spectrum Bridge, Key Bridge Global, Telecordia/iconectiv, etc.) for channels available to microphones in their locale. We generally recommend that wireless microphone owners and operators begin replacing 600 MHz equipment now and plan completion of their transition well before the final July 13, 2020 deadline.

  • The two microphone reserved channels that currently exist in each geographic market are being eliminated. However, portions of the guard band and duplex gap will be available for the exclusive use of wireless microphones.

  • The FCC has proposed that a reserved UHF TV white space channel exist in every market area, but a final decision is pending. This channel would be shared between wireless microphones and white space devices (explained below), but could be reserved by licensed microphone operators for eligible events.

  • The FCC will require manufacturers, distributors, integrators, and retailers that sell or lease 600 MHz wireless microphone systems to post notices at the point-of-sale, on websites, on packaging, and in literature about vacating 600 MHz and the new operating rules.

New UHF Band Plan

The FCC’s incentive auction had a multi-stage structure designed to repurpose up to 144 MHz of TV band spectrum, depending on various scenarios. Ultimately, only 84 MHz (614-698 MHz) will be repurposed. Although the auction poses big challenges for many wireless microphone owners and operators, this outcome repurposes less TV band spectrum than some observers within the audio industry had feared.

UHF Channel 37 (608–614 MHz) has not been used for TV broadcast. Rather, it has been used for wireless medical telemetry (“WMTS”) (e.g., monitoring a patient’s vital statistics in a hospital). It has also been used in a few remote geographic areas for radio astronomy (“RAS”) studies. Wireless microphones have never been permitted to operate on Channel 37, and this is not changing.

This leaves the majority of the UHF TV band (Channels 14-36) allocation unchanged. Accordingly, any locally-vacant (i.e., white space) channel within this range remains available to wireless microphones. This is important because the frequencies within this portion of the UHF TV band have very favorable characteristics, including: signals that can travel through walls, devices that achieve extended range from low transmitter power, and devices that utilize compact antennas. A prime message conveyed to the FCC by many audio industry leaders was that the UHF TV band must remain part of the spectrum portfolio available to wireless microphones – especially for hypercritical applications.

White Space Devices

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. WSD 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 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.

Reserved Channel

The FCC has issued a Notice of Proposed Rulemaking to reserve at least one UHF TV channel in every market for shared use by wireless microphones and WSDs, but has not yet made a final decision. The possibility exists that the new FCC leadership may reverse course on this issue. Regardless, many areas, particularly suburban and rural ones, are likely to have more than one white space channel. As noted above, eligible wireless microphone operators can reserve any locally-vacant TV channel for their event, preventing WSDs from operating on these channels during the production. This is done through any one of the FCC-approved white space database administrators. Once a reservation is entered, the information is automatically shared within minutes to all database administrators. Since the number of WSDs could increase significantly, registering for protection will become more critical in the future for wireless microphone operators.

Faster Database System

Currently, WSDs “pull” information by polling from the database once a day. In the future, white space database administrators will “push” information about changes in channel availability to WSDs operating in an area requiring protection of licensed wireless microphones – with the result that these channels can be reserved in about 20 minutes. This is a significant reduction in time compared to the current WSD polling method, which could take nearly 48 hours to ensure channel clearing. This greatly benefits news teams and other audio professionals covering late breaking events.

Co-Channel Operation with TV Station

The Commission revised its rules for the operation of wireless microphones on the same channel used by a TV station (referred to as “co-channel operation”). 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 field strength benchmark, rather than the traditional geographic separation from TV transmit antennas, opened a number of UHF TV channels to wireless microphone operations that would otherwise not be permitted.

Operating in the Guard Band & Duplex Gap

An 11 MHz buffer band known as the duplex gap has been established between the forthcoming downlink and uplink 600 MHz mobile broadband blocks. No devices shall operate in the lowest 1 MHz adjacent to the downlink block. The next 4 MHz (653-657 MHz) are reserved for licensed wireless microphone operators, and will not be shared with white space devices. This will be particularly useful for electronic news gathering (“ENG”) crews covering spontaneous events. In contrast, the upper 6 MHz (657-663 MHz) of the duplex gap will be shared between unlicensed wireless microphones and white space devices.

A 3 MHz lower guard band will exist, separating mobile broadband from Channel 37. No devices shall operate in the upper 1 MHz (616-617 MHz) adjacent to the downlink block. Wireless microphones will have exclusive use of the remaining 2 MHz (614-616 MHz), and will operate under FCC Part 15 unlicensed rules.

Power output of wireless microphone transmitters will be limited to 20 milliwatts (mW) effective isotropic radiated power (“EIRP”) when operating in the guard band or duplex gap. This specification was traditionally measured as conducted power at the transmitter’s antenna terminal. EIRP, a measurement based on use of a theoretical isotropic omnidirectional antenna, will yield slightly different results. 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.

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. This means that licensed wireless microphone operators will have no priority or rights to reserve these pockets, unlike TV white space channels.

The Commission envisions that the repurposed spectrum band plan will be uniform nationwide. This is an advantage for wireless microphone operators using the guard band and duplex gap in touring applications.

Licensed Versus Unlicensed Wireless Microphone Operations

The FCC is making a clearer distinction between licensed and unlicensed wireless microphone operations. Broadcasters, motion picture producers, cable stations, and creators of content for over-the-air broadcast have traditionally been eligible for a Part 74 license. License eligibility has been expanded, and now includes venues and sound companies routinely using 50 wireless microphones or more. The key word here is “routinely.” Therefore, eligibility does not require that every performance use 50 wireless microphones. Remember to consider that ear monitors, intercom channels, and similar devices are included in that count. The Commission plans to expand license eligibility further through an additional rulemaking. This is good news for professional performing arts companies that use fewer than 50 wireless microphones. All eligible parties should apply for licensed status to take advantage of the rights and privileges afforded to them, including registration for interference protection from WSDs in the white space database system as well as access to additional licensed bands outside of the UHF TV band. To apply to become a licensed wireless microphone operator under the service referred to as “Broadcast Auxiliary - Land Mobile (Part 74)”, or under FCC’s Part 90 rules, file FCC Form 601 electronically by using the FCC’s Universal Licensing System found at http://wireless.fcc.gov/uls/.

Wireless microphones are subject to FCC equipment authorization. Some equipment will be certified only for Part 74 (or Part 90) licensed operation, and unlicensed operators will not be permitted to operate it. Some equipment will carry Part 15 certification only, and should be operated under FCC’s unlicensed rules regardless of the operator’s licensing status. Other equipment will carry both Part 74 and Part 15 certifications.

Access to Alternate Frequency Bands

The FCC recognized that wireless microphones are essential for content creation, live stage events, and a wide variety of civic activities. The Commission made a commitment to accommodate current and future demand of wireless microphone operators partially through access to alternative frequency bands outside of the UHF TV band, as well as favorable modifications to certain operational rules, including:

  • The current 944-952 MHz studio transmission link (“STL”) band has effectively been expanded to include portions within the 941-960 MHz band (specifically 941.500-944.000 MHz; 944.000-952.000 MHz; 952.850-956.250 MHz; 956.450-959.850 MHz) and is open to all licensed wireless microphone operators. Previously, the STL band was limited to licensed wireless microphone operators that were broadcasters. Primary services in this band are point-to-point fixed Microwave Services and Broadcast Auxiliary Services (BAS). Operation should be coordinated with the local Society of Broadcast Engineers (“SBE”) frequency coordinator. To operate within 941.5–944 MHz, wireless microphone licensees will first need to coordinate with the local SBE coordinator and then apply for a license with the FCC, which will coordinate with incumbent Federal primary users of the band. This band can be useful for fixed venues, such as casinos, that need “house mics” on distinct frequencies from travel acts. Broadway theaters are another example of potential users.

  • The rules governing the 169-172 MHz band (which lies just below high band VHF TV channels) were revised to make this range more practical for wireless microphones. Specifically, the Commission adopted Sennheiser’s proposed channelization that will allow more wireless microphones to operate simultaneously in this band. Operation will be on discrete frequencies, and will be uniform nationwide – an advantage when traveling throughout the United States. A Part 90 license is required but eligibility is broader than for a Part 74 license. FCC states: “Entities eligible to operate wireless microphones under the Part 90 rules include a variety of users, including those eligible to hold LPAS licenses under Part 74 as well as many other entities, such as state and local government entities; commercial entities in general; educational, philanthropic or ecclesiastical institutions; clergy; and hospitals, clinics, and medical associations.” The Commission further explains, “While all entities eligible for license under Part 74 are also eligible under Part 90, the inverse is not true: many entities eligible under Part 90 are not eligible under Part 74.” The application process for a Part 90 license follows the same procedures as that for Part 74, described above.

  • The 1435-1525 MHz band (i.e., the 1.4 GHz band) will be available to licensed wireless microphone operators. However, use of this band will require equipment with an electronic key (yet to be introduced in the market), and an approval process for each production. This band is intended for “power users” – those requiring around 100 wireless microphones or more, at fixed locations (as opposed to mobile news teams). Operation in this band will be secondary to aeronautical mobile telemetry (“AMT”) (i.e., flight testing). The 1.4 GHz band is coordinated by the Aerospace and Flight Test Radio Coordinating Council (“AFTRCC”). Equipment must incorporate location, date, and time awareness. AFTRCC will provide a digital code (i.e., the electronic key) that will unlock the equipment, enabling the device to work at the approved time and location. There is a 30 MHz spectrum use limit when operating in this band. However, multiple authorizations that, in total, utilize the full 90 MHz may be assigned to different operators within an area (e.g., three Broadway shows in adjacent theaters each could get distinct sets of 30 MHz). A single operator that requires more than 30 MHz for a mega-event can apply for an FCC special temporary authorization (“STA”). Several details still need to be worked out between the audio industry and AFTRCC, including creation of a portal by our industry to funnel applications to AFTRCC.

  • The 6875-6900 MHz and 7100-7125 MHz bands are available to licensed wireless microphone operators. These two 25 MHz blocks are the “bookends” of a range that is assigned to wireless video. Therefore, audio engineers should be coordinating their use with their video counterparts. The short wavelengths of these high frequency bands will largely limit their usefulness to short range, line-of-sight applications (e.g., a reporter using a handheld microphone transmitter standing directly in front of a video camera equipped with the mating microphone receiver).

Equipment that can be Purchased with Confidence

The continued availability of lower UHF frequencies, together with the access recently gained in several alternate frequency ranges, ensures that the future includes plenty of wireless microphones. Many wireless microphone systems have been introduced in unlicensed ranges (e.g., the 902-928 MHz, 1.9 GHz (DECT), and 2.4 GHz bands) in part due to the uncertainty posed by the auction. Such systems work fine in these unlicensed bands if the RF environment in which the systems operate is tame. Unlicensed bands, however, are open to a plethora of devices (e.g., cordless telephones, wireless routers, drones, robots, etc.) so interference can occur among devices operating in close proximity to each other. For users who do their homework, the UHF band is more predictable because its use is limited to specific devices and services. Therefore, UHF is still preferred for professional and many semi-professional applications. It is important to keep in mind that any wireless microphone with the ability to tune to any frequency within the repurposed spectrum will need to be taken out of service before the end of the transition period. Customers can confidently acquire any UHF system that does not have the ability to tune above TV Channel 36 (608 MHz). In the future, if you need to configure systems with a large number of wireless microphones requiring more spectrum than the UHF TV band can accommodate, it is important to determine if the operator qualifies for a Part 74 license. Licensed operators would be best served by first adding additional wireless microphones in the 941-960 MHz band, and then applying for use of 1.4 GHz for mega-installations. Unlicensed operators can add additional microphones in the guard band, duplex gap, and the various bands that are available to unlicensed devices.

Our Commitment Continues

Ever since the dawn of radio, policies regarding the use of spectrum have continually changed – that will not end with the outcome of this incentive auction. It is important to recognize that the incentive auction centered around how content is distributed. Adequate spectrum for wireless microphones is also essential for content creation. The United States is the undisputed global leader in news and entertainment content. U.S. core copyright material is a $1 Trillion industry (that’s Trillion with a “T”), and has a 3-to-1 export-to-import ratio – the highest of any American-made product or service. Demand for recorded content and live events remains robust, and the trend for increasingly sophisticated productions will continue. Wireless microphones are not merely a convenience, they are indispensable tools fueling this ecosystem. Sennheiser is committed to work cooperatively with the FCC so that the Commission fully understands the importance and ubiquitous nature of wireless microphone operation in our society, and the challenges that spectrum repurposing poses. Our goals are to minimize the adversities that such changes could cause, and to ensure that wireless microphone use for live and recorded events will continue uninterrupted while meeting future demands. We thank all of our colleagues and customers who support our efforts – especially those who wrote to and/or even met with FCC staff, thus fortifying a fertile future for our industry.

About the Author:

Joe Ciaudelli is Director of U.S. Spectrum Affairs for Sennheiser Innovation & Research. He is a private sector advisor in the U.S. delegation to the international Telecommunications Union (ITU), the United Nations specialized agency on information and communications. He is also the founder of Rayvel, a corporation that specializes in electro-magnetic science, and holds three patents in holographic technology.