FCC Part 15 and Part 74 Wireless Regulations

The FCC (Federal Communications Commission) governs RF spectrum usage in the United States through multiple regulatory frameworks. For AV integrators, understanding Part 15 (unlicensed devices) and Part 74 (broadcast auxiliary services) is critical when designing wireless microphone systems, distributing unlicensed wireless devices, and ensuring RF coexistence.

FCC Part 15 and Part 74 define which frequency bands AV wireless devices can operate on, what power levels are permitted, licensing requirements, and coordination obligations. The 600 MHz repack (2017) fundamentally shifted wireless microphone design by reclaiming broadcast spectrum, making frequency coordination more essential than ever.

Part 15 permits RF equipment to operate on designated frequency bands without an FCC license, provided the device meets strict technical standards and accepts potential interference.

2.4 GHz (2400–2483.5 MHz): Shared by Wi-Fi, Bluetooth, Zigbee, cordless phones, microwave ovens
- High congestion; interference common in crowded RF environments
- Typical wireless microphone frequency in cost-sensitive applications
5 GHz (5150–5925 MHz): Wi-Fi and unlicensed point-to-point links
- U-NII bands with UNII-1 through UNII-4 subdivisions
- Lower congestion than 2.4 GHz; shorter range
- Increasingly used for professional wireless mics and IEM systems
900 MHz (902–928 MHz): Legacy cordless phones, some wireless mics
- Lower congestion than 2.4 GHz; better range
- Fewer modern devices competing; favorable for AV

FCC certification: Device must be tested and approved before sale
RF power limits: Strictly defined by band; typically −20 dBm EIRP for 2.4/5 GHz
Frequency stability: Must remain within assigned band; no intentional frequency hopping into licensed bands
No protection from interference: Unlike licensed users, Part 15 devices have zero interference protection. Wi-Fi, cell phones, or medical equipment can render them inoperative.

Part 15 devices are affordable and license-free but inherently unreliable in RF-dense environments
Suitable for: corporate training, small meetings, non-critical presentations
Not suitable for: live events, mission-critical broadcasts, medical facilities, government, legal proceedings

Part 74 authorizes professional wireless microphone operators to use licensed spectrum with FCC protection and coordination obligations. Part 74 users receive interference protection unavailable to Part 15 operators.

VHF Band (136–175 MHz)

Historically primary band for professional wireless mics
Lower RF propagation; requires more transmitter power
Long-range coverage (stadium, outdoor events)
Licensing cost moderate; frequency availability declining

UHF Band (470–698 MHz) — CRITICAL POST-600 MHz REPACK

Historically the premium band for professional wireless (channel 14–51)
Superior RF propagation indoors and outdoors
600 MHz repack (2017) eliminated channels 36–51 for terrestrial broadcast use
Modern professional wireless now operates: 566–608 MHz (TV channels 14–20 only)

White Space Devices (500–700 MHz)

Secondary access to unused TV broadcast channels
Requires FCC approval and database registration
Available in specific geographic areas only
Dynamic frequency selection (automatic band-switching) required
Useful backup for wireless mics when dedicated spectrum unavailable

Pre-2017: Wireless mic systems used TV channels 36–51 (614–698 MHz) as primary operating spectrum with excellent propagation and capacity.

Post-2017: Channels 36–51 reallocated to mobile carriers. Professional wireless mics relocated to channels 14–20 (566–608 MHz), creating:

Reduced spectrum availability: 24 MHz (channels 14–20) vs. 84 MHz (channels 14–51)
Increased RF congestion: Fewer channels for larger event populations
System redesign: Multi-system operators must re-inventory and reprogram legacy wireless mics
Coordination complexity: Increased need for RF frequency coordination software and survey

Part 74 wireless mics operate on licensed frequencies, but integrators cannot simply choose any frequency. Frequency coordination is mandatory:

Coordination entities: FCC-approved organizations (Coordinating Committee for TV Relay Stations) maintain interference-free frequency assignments
Pre-deployment survey: RF spectrum analyzer scan of proposed venue to identify occupied frequencies
Coordination database: Request frequency assignment from coordination entity; system assigned interference-free channels
Event license: Temporary authorization issued for specific event/duration
Monitoring: During event, monitor assigned frequencies for unexpected interference

Annual license fee: Per-frequency cost varies by region; typically $100–$400 per frequency per year
Multi-system operations: Larger events may require 10–20+ frequencies; total licensing cost can reach $4,000–$8,000 annually
Coordination fees: Coordination entities charge nominal fees (typically $50–$150 per frequency)

Corporate meetings, training sessions, small rooms
Backup systems (never primary in critical applications)
Budget-constrained projects where RF reliability is secondary

Large meetings (100+ attendees)
Live events, broadcasts, productions
Mission-critical applications (boardrooms, government, legal)
Environments with dense RF (convention centers, hotels, venues)
Any application requiring guaranteed RF availability

Pre-site survey: Use spectrum analyzer to identify occupied UHF channels
Identify candidates: List clear/available channels from 566–608 MHz
Contact coordination entity: Request frequency assignment for event date/time
Obtain temporary license: Coordination entity issues Part 74 authorization
Program system: Load assigned frequencies into wireless mic transmitters/receivers
Deploy & monitor: Continuously monitor for interference during event
Document: Maintain coordination records for compliance audit trail

Determine RF environment density (venue RF survey completed)
Select licensed (Part 74) or unlicensed (Part 15) based on criticality
If Part 74: initiate coordination 4–6 weeks pre-event
Verify system frequency range operates in post-600-MHz compliant bands (566–608 MHz for UHF)
Budget for annual licensing/coordination fees
Maintain spectrum analyzer and RF survey capability on-site
Train operators on interference detection and fallback procedures

Assuming old UHF mics still work: Legacy systems programmed for channels 36–51 will not operate post-repack. Reprogramming or replacement mandatory.
Skipping coordination: Operating Part 74 without coordination invitation creates regulatory violation and interference risk.
Relying on Part 15 for critical events: Unlicensed wireless is inherently unreliable and should never be sole system for high-stakes presentations.
Underestimating coordination lead time: Frequency coordination can take 2–4 weeks; plan accordingly.
Ignoring white space availability: For reduced-licensing-cost backup systems, white space databases can identify available spectrum post-600 MHz.

FCC Part 15 and Part 74 Wireless Regulations

Overview

FCC Part 15: Unlicensed RF Devices

Key Concept

Unlicensed ISM Bands (Industrial, Scientific, Medical)

Part 15 Compliance Requirements

Integrator Implications

FCC Part 74: Licensed Wireless Microphones (Broadcast Auxiliary Services)

Key Concept

Licensed Bands for Wireless Microphones

VHF Band (136–175 MHz)

UHF Band (470–698 MHz) — CRITICAL POST-600 MHz REPACK

White Space Devices (500–700 MHz)

600 MHz Repack Impact

Frequency Coordination

Part 74 Licensing & Costs

Practical Application

When to Use Part 15 (Unlicensed)

When to Use Part 74 (Licensed)

RF Survey & Coordination Workflow

Wireless Mic System Design Checklist

Common Pitfalls

Related