FCC Regulations and EIRP Reference

Operating LoRa mesh equipment in the United States requires compliance with FCC Part 15 rules. This page summarizes the relevant regulations and explains how to calculate whether your installation is within limits.

Disclaimer: This page is a general reference for community operators. It is not legal advice. For installations with high-gain antennas or unusual configurations, consult the FCC rules directly (47 CFR Part§ 15)15.247, eCFR) or a licensed RF engineer.

Rules summarized as of June 2026.

The 915 MHz ISM band

LoRa mesh in North America operates in the 902 - 902–928 MHz band, designated as an ISM (Industrial, Scientific, and Medical) band. This band is available for unlicensed operation under FCC Part 15, Subpart C (Intentional Radiators).

Key rule: FCC Part§ 15.247 governs spread-spectrum and digitally modulated operation in the 902 - 902–928 MHz band.

Power limits

Limit type Value InNotes other units Conducted output power 1 W (30 dBm) Maximum power at the antenna port (conditions below) EIRP (Effective Isotropic Radiated Power) 4 W (36 dBm) Conducted power + antenna gain Antenna gain above 6 dBi Reduce conducted power dB-for-dB above 6 dBi EIRP withstays directionalcapped antennaat 36 dBm — § 15.247(b)(4)Special rules applySee below

ForThere is no extra EIRP allowance at 902–928 MHz — not even for fixed point-to-point linkslinks. usingIf your antenna gain exceeds 6 dBi (common with directional antennas (Yagi, dish)), FCC Partrules require you to reduce conducted transmit power by the full amount the gain exceeds 6 dBi (47 CFR § 15.247(b)(3)4)), provideswhich ankeeps additionalmaximum EIRP at 36 dBm (4 W) in every configuration. Example: a 9 dBi Yagi limits you to 27 dBm conducted; a 12 dBi antenna to 24 dBm.

You may have read about point-to-point gain allowances in § 15.247 — those provisions (§ 15.247(c)(1)) apply only to the 2.4 GHz and 5.8 GHz bands, not to 902–928 MHz. Canada's RSS-247 works the same way: its point-to-point exception also excludes 902–928 MHz.

Conditions behind the 1 W figure

The 1 W ceiling applies to qualifying system types: digitally modulated systems with at least 500 kHz of 6 dB bandwidth (§ 15.247(a)(2)), or frequency-hopping systems with at least 50 hopping channels (§ 15.247(b)(2); systems with 25–49 channels — permitted only when the hopping channel's 20 dB bandwidth is 250 kHz or greater, § 15.247(a)(1)(i) — are limited to 0.25 W). Digitally modulated systems are additionally limited to 8 dBm of power spectral density in any 3 dBikHz ofband EIRP(§ allowance15.247(e)). forCommon everyLoRa 3mesh dBipresets ofuse antenna125–250 gainkHz abovebandwidth, 6so dBi,your updevice's FCC certification grant — not the rule's 1 W ceiling — defines what it is authorized to transmit. Operating a maximumcertified gaindevice limit.in Thisits exceptionstock enablesconfiguration long-rangeis fixedthe linkssafe - but it does NOT apply to general area coverage nodes.harbor.

EIRP calculation

EIRP (dBm) = TX Power (dBm) + Antenna Gain (dBi) − Cable Loss (dB)

Example 1: TypicalStock rooftopnode repeaterwith a small upgrade antenna (within limits)

Parameter Value TX power 2722 dBm (500stock mW)SX1262-class board) Cable loss (3m3 m LMR-200) −0.31.0 dB Antenna gain +5 dBi EIRP 27 − 0.322 + 5 − 1.0 = 31.726.0 dBm (below 36 dBm limit ✓)

Example 2: PA-equipped rooftop repeater (within limits)

Parameter Value TX power 27 dBm (500 mW — PA-equipped/base-station class) Cable loss (3 m LMR-200) 1.0 dB Antenna gain +5 dBi EIRP 27 + 5 − 1.0 = 31.0 dBm (below 36 dBm limit ✓)

Note: 3 m of LMR-200 loses about 1.0 dB at 900 MHz (Times Microwave datasheet: ~32.6 dB/100 m). Thinner cables lose more; budget for your actual cable type and length.

Example 3: High-gain antenna requiring power reduction

Parameter Value TX power (attempted) 30 dBm (1W1 maximum)W) Cable loss−0.5 dB Antenna gain +9 dBi Required reduction Antenna gain exceeds 6 dBi by 3 dB → reduce conducted power by 3 dB EIRPMaximum legal TX power 3027 dBm (47 CFR § 15.247(b)(4)) Resulting EIRP 27 + 9 − 0.5 + 9(cable) = 38.35.5 dBm (exceedswithin 36 dBm -✓) ILLEGAL) Required TX power reduction38.5 − 36 = 2.5 dB, so reduce TX to 27.5 dBm

The reduction is computed from antenna gain alone — cable loss does not offset it. In Meshtastic, set LoRa config → Transmit Power to 27 (integer dBm; always round down).

Standard device compliance

CommerciallyMany soldmainstream LoRa boards (Heltec,LILYGO T-Beam,Beam RAK4631,— FCC ID 2ASYE-T-BEAM, RAK4631 — see RAK's certification page, Heltec, etc.) arecarry FCC-certifiedFCC atcertification covering their maximumshipped powerconfiguration. settingsCheck withthat theyour stockspecific antenna.board has an FCC ID — uncertified clones are common. If you use thea certified device as shipped with the included antennaantenna, or with a comparable-replacement antenna of the same type and equal or lower gain replacement,(47 you'reCFR § 15.204(c)(4)), you are within the certification. A different antenna type or higher gain — even a "comparable" one — is not covered, and compliance responsibility shifts to you.

Custom installations -— especially with high-gain external antennas or increased TX power settings -— require you to verify EIRP compliance independently.

What happens if you exceed the limits?

FCCExceeding the limits is a violation of federal rules regardless of how likely enforcement ofis. The FCC can issue warnings and monetary forfeitures, and any Part 15 violationsoperator ismust uncommonstop fortransmitting small-scaleif communitynotified meshthat deployments,they butare thecausing harmful interference (47 CFR § 15.5). The rules also exist for good reason: excessive EIRP creates interferenceinterferes with other users of the bandband, including industrial IoT systems, 900 MHz ISM devices, and legacylicensed systems.services.

More practically: running higher power than necessary increases interference with nearby mesh nodes and doesn't improve range as much as better antenna placement would. For most installations, 27 - 30 dBmstock TX power with a 3 - 3–6 dBi antenna at a better location is the right operating point.

Fixed installations are also subject to FCC RF-exposure rules (§ 15.247(i)); keep antennas away from areas people occupy.

Canada (ISED) rules

Industry Canada (now Innovation, Science and Economic Development Canada -(ISED, ISED)formerly Industry Canada) rules for 902 - 902–928 MHz operation are similar to FCC Part§ 15.247. The relevant standard is RSS-247.247 (with RSS-Gen general requirements). Conducted power limit is also 1W;1 W; EIRP and antenna-gain reduction rules align with FCC.the FCC's, and RSS-247's point-to-point exception likewise does not cover 902–928 MHz. Certified devices sold in both markets carry both FCC and IC certification numbers.

Frequency coordination

The 902 - 902–928 MHz band is shared with many other services and devicesdevices, including:

Federal radiolocation systems (primary users) — high-EIRP government radars; you must accept their interference Part 18 ISM equipment — Part 15 devices are secondary to it Amateur radio (33 cm band) — licensed hams may also run mesh hardware at higher power under Part 97 (47 CFR § 97.313(j)) Other LoRa/LoRaWAN deployments 900 MHz WiFiWi-Fi (802.11ah/HaLow) Legacy 900 MHz consumer devices (older pre-DECT cordless phonesphones, (some models) ISM industrial/scientific equipment Some baby monitors and older wireless phonesmonitors)

ThePart band15 operation is unprotected: you must accept interference from these services and must not cause harmful interference to them (47 CFR § 15.5).

Meshtastic and MeshCore each transmit on a single configurable channel frequency — they do not automatically frequency-hoppedhop. or channel-selectable - ifIf you experience unusual interference, trymanually select a different sub-channel frequency. Both MeshCore and Meshtastic allow channel frequency adjustmentslot within(Meshtastic: LoRa config → Frequency Slot; MeshCore: set freq via the ISMserial band.CLI on repeaters/room servers, or the app's radio settings on client nodes). Coordinate with other operators in your area to avoid overlapping on the same exact frequency.