FCC Part 15 Compliance for LoRa Mesh

Meshtastic and MeshCore operate in the 902-928 MHz ISM band under FCC Part 15 in the United States. This section explains what the rules require, what they allow, and what you need to know for compliant operation.

FCC Part 15 Basics

Part 15 covers unlicensed intentional radiators - devices that deliberately emit radio frequency energy. The key rules for 902-928 MHz spread spectrum:

• Maximum conducted power: 1 watt (30 dBm) - Measured at the radio's antenna connector, before any external antenna
• Maximum EIRP: 4 watts (36 dBm) - Effective Isotropic Radiated Power, accounting for antenna gain. EIRP = Conducted Power + Antenna Gain (dBi) - Cable Loss (dB)
• No license required for operation within these limits
• Non-interference - Part 15 devices must accept interference and cannot cause harmful interference to licensed services
• No protection from interference - You have no recourse if a licensed service interferes with your mesh

The 1W + Antenna Gain Calculation

Most LoRa hardware ships configured at or below 1W (30 dBm) conducted power. If you add a high-gain external antenna, you must reduce conducted power to keep EIRP under 36 dBm.

Example calculation:

Conducted power: 27 dBm (500 mW)
Antenna gain: +6 dBi
Cable loss: -1 dB
EIRP: 27 + 6 - 1 = 32 dBm (1.6W) - COMPLIANT (under 36 dBm)

Second example:
Conducted power: 30 dBm (1W)
Antenna gain: +9 dBi
Cable loss: -1 dB
EIRP: 30 + 9 - 1 = 38 dBm (6.3W) - NON-COMPLIANT (exceeds 36 dBm)

For typical community deployments with 5-6 dBi antennas and short coax runs, full 1W conducted power is generally compliant. With 8-9 dBi antennas, you should reduce conducted power to 27-28 dBm.

Point-to-Point Operations (Fixed Infrastructure)

FCC Part 15.247(b)(3) allows an increased EIRP limit for fixed, point-to-point operations:

• For a directional antenna used in a fixed link (not general area coverage): the 1 dBi rule - you may increase EIRP by 1 dB for each 1 dBi of antenna gain above 6 dBi, up to a maximum of 30 dBm conducted + the antenna gain
• This applies to point-to-point links only - not omnidirectional antennas for area coverage

Pre-Certified Hardware

All commercial Meshtastic and MeshCore hardware sold legally in the US is pre-certified under FCC ID. This certification confirms Part 15 compliance when used with the included antenna and at the specified power levels. Using third-party antennas or modifying conducted power beyond the certified levels may affect compliance status. For community mesh operations, using hardware within its certified parameters is the simplest path to compliance.

What Part 15 Does NOT Require

• No license - operators need no FCC authorization
• No station identification - Part 15 devices do not require ID (unlike Part 97 ham radio)
• No frequency coordination - you may operate anywhere in the 902-928 MHz band without coordination
• No notification of your installation