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High-Power Mountain Repeater Build (~$200)

⚠ FCC COMPLIANCE WARNING — READ BEFORE BUILDING: Under FCC Part 15 (47 CFR §15.247) the 902–928 MHz band has a hard conducted-output ceiling of 1 W (30 dBm) at the coax, referenced to an antenna of up to 6 dBi. This conducted limit applies before antenna gain is considered, and the derived EIRP ceiling is 36 dBm (4 W) with a 6 dBi antenna (above 6 dBi, conducted power must be reduced 1 dB for every 1 dB of gain). An external RF amplifier almost always pushes conducted output over 30 dBm, which is illegal for unlicensed Part 15 operation. A "2 W" (33 dBm) amplifier exceeds the limit outright and must not be used unlicensed. Higher power is only lawful under an amateur (Part 97) license — and Part 97 prohibits encryption (47 CFR §97.113(a)(4)), so Meshtastic/MeshCore default AES channels must be turned OFF, and you must identify by callsign at least every 10 minutes (§97.119). Measure your conducted output with a power meter before deploying.

This build is designed for demanding deployments - mountain summits, ridge lines, or any site that needs extended range and the ability to survive winter conditions. It pairs a LilyGO T-Beam with a 1 - 2W power amplifier module, a LiFePO4 battery bank,bank and a robust MPPT charge controller. Note that any external RF amplifier option must be operated within the FCC limits described in the warning above — under Part 15 the total conducted output may not exceed 1 W (30 dBm), and most "1 W" amplifier modules will only be legal if the modem drive is reduced so the amplifier's output stays at or below 30 dBm conducted. A 2 W amplifier cannot be operated legally under Part 15.

Parts List

Prices are approximate and volatile (as of 2026-06-08); verify current pricing and component availability before ordering.

PartApprox. Cost
LilyGO T-Beam v1.1 (ESP32 + SX1276/SX1262 + GPS + 18650 holder). Note: v1.1 has been largely superseded by v1.2; SX1276 variants max ~17-20 dBm vs SX1262 ~22 dBm.~$35
ZebraHatDocumented 1WLoRa power amplifier board or Ikoka 2W RF power-amplifier module (verify the datasheet — e.g. a RAKwireless 1 W LoRa booster or a documented E22-900M30S module). A 1 W (30 dBm) PA is the maximum that can be made Part-15-legal, and only if the modem drive is reduced so the PA output does not exceed 30 dBm conducted. Do NOT use a 2 W (33 dBm) module for unlicensed operation — it exceeds the FCC limit.)~$4540 - 60
10W 12V monocrystalline solar panel~$20
Genasun GVB-8 or Victron SmartSolar 75/10 MPPT charge controller (the ~$35 low end may be optimistic for a genuine MPPT unit)~$35 - 7090
LiFePO4 battery, 12V 10Ah~$45
Inline fuse (3-5 A) for the battery positive lead, plus a battery disconnect/switch~$5
Fibox TEMPO 11×9×5" weatherproof polycarbonate enclosure (confirm the exact part number, dimensions, and stated IP rating — Fibox TEMPO is rated IP65/IP66/IP67 depending on the listing)~$30 LMR-200 low-loss coax, 1m + N-type connectors (crimped or soldered)~$15 6 dBi fiberglass omni antenna, N-type, 915 MHz (real gain must be at or below 6 dBi to stay within 36 dBm EIRP at full legal conducted power)~$25 Mounting hardware (J-pipe mount, stainless U-bolts, mast)~$20 Total~$200 - 250

Key Design Considerations

Power Amplifier & Heat Management

TheA ZebraHatLoRa andpower-amplifier Ikokamodule modules both requirerequires a 12V supply rail (typically 12V, taken directly from the LiFePO4 battery or a regulated 12Vbus bus)— check the specific module's input voltage and current spec). At ~1W continuousRF TXoutput duty,with a typical class-AB PA efficiency around 25%, the amplifier draws ~4W DC and dissipates roughly 3W as heat.heat (actual figure depends on the module's efficiency, typically 2-4W). Mount the amplifier board against an aluminum bracket that contacts the enclosure wall, or add a small heatsink with thermal paste. Without adequate thermal management, output power will derate and long-term reliability will suffer.

EIRP & Regulatory Compliance

Under FCC Part 15 at 902-928 MHz (47 CFR §15.247) the limit is 30 dBm (1 W) conducted at the coax with an antenna of up to 6 dBi gain. For antennas above 6 dBi, conducted power must be reduced 1 dB for every 1 dB of gain above 6 dBi. Combining a true 1W (30 dBm) amplifierconducted output with a 6 dBi antenna producesyields 36 dBm EIRP -— rightand that 36 dBm EIRP figure is the derived ceiling only with a 6 dBi antenna at thefull FCClegal Partconducted 15power; limitit foris unlicensednot 915a MHzuniversal operation.fixed limit. Confirm the antenna gain rating is measured (not marketing-inflated)., and treat 36 dBm EIRP as a target to stay under (with margin), accounting for feedline and connector loss. Verify by measurement rather than trusting nameplate numbers. The conducted limit governs first: an external amplifier that produces more than 30 dBm at the coax is non-compliant regardless of antenna gain.

If you hold an amateur radio license (Technician or above), you canmay operate at higher power levels under Part 97, but with important conditions: (1) you must DISABLE all encryption — Meshtastic/MeshCore default AES channels are prohibited under 47 CFR §97.113(a)(4); use an unencrypted/open protocolchannel; (2) you must transmit station identification by callsign at least every 10 minutes per §97.119; (3) the 33 cm band is secondary for amateurs and identifyautomatic-control byand callsign.content rules apply; and (4) you must perform an RF-exposure (MPE) evaluation per FCC §1.1310, as a high-power amplifier at antenna height creates an exposure zone requiring a keep-away/safe-distance assessment. Do not operate default-encrypted mesh firmware at amateur power levels. See the regulatory guidance page before transmitting at amateur power levels.

LiFePO4 Chemistry for Cold Deployments

LiPo (Li-ion) cells can lose uproughly to20-30% 50%of usable capacity atnear 0°C and must NOT be charged below freezing (0°C / 32°F) — charging below 0°C causes lithium plating, which permanently damages the cell and creates a fire risk. LiFePO4 cells discharge to about -20°C with reduced capacity, but should not be charged below freezing.0°C at normal rates either. Some BMS-equipped or self-heating LiFePO4 cellspacks retainpermit ~80%charging capacitybelow freezing only at drastically reduced current (≈0.1C below 0°C, then ≈0.05C below -20°C10°C). andCritically, cana LiFePO4 pack must be safelypaired charged down to -10°C (with a BMSLiFePO4-appropriate thatcharger/controller supports(3.6 V/cell charge profile) and a low-temperature charge cutoff).cutoff; charging LiFePO4 on a standard 4.2 V Li-ion charge profile will overcharge it. The single safe rule to remember: do not charge any lithium chemistry below 0°C. For any deployment above 1500m elevation or at latitudes above 40°N, LiFePO4 (with a correct charger and low-temp cutoff) is strongly recommended over LiPo.

Winter Solar Harvest

A 10W panel mounted at a 30° south-facing tilt at 45°N latitude deliversmay approximatelydeliver on the order of 15 - 20 Wh/day at winter solstice.solstice under clear skies, but this is a rough estimate — actual yield is highly site- and weather-dependent and should be modeled for your specific location with a tool such as PVWatts or PVGIS. Note that 30° tilt is suboptimal for winter at 45°N (≈60° captures more low-angle winter sun), and on overcast winter days small panels in low-sun regions (e.g. the Pacific Northwest "Big Dark") can produce only ~3-5 Wh/day. The system draws roughly 5W peak during transmit (≈1W RF plus PA inefficiency + ESP32 + GPS) and muchfar less on average with duty-cycling.cycling; Thisproduce yielda ismeasured, sufficientitemized forpeak and average power budget rather than relying on the estimate.

Whether this harvest sustains a 24/7 repeater with multi-day overcast reserves depends entirely on the verified site-specific harvest figure and the real average load. Tie the conclusion to a measured days-of-autonomy calculation; in low-sun regions deployed builders use larger or multiple panels precisely because small panels underperform in overcast winters, so a single 10W panel may be insufficient — size the panel and the 10Ah battery providingto overnightyour andmodeled multi-dayworst overcast reserves.case.

Coax Loss Matters at 1W915 MHz

RG58At ~915 MHz, RG-58 loses approximately 2.0.5 dBdB/m per(~16.5 meterdB/100 atft) 915 MHz.and LMR-200 losesabout 0.33 dB/m (~9.9 dB/100 ft). Over a short 1 m run the difference between the two is only about 0.2 dB (~0.95% dB/m.more Atradiated 1Wpower) transmit— powereffectively withnegligible. aCoax 1mchoice run,matters switchingon fromlonger RG58runs: at ~10 m the difference grows to LMR-200roughly recovers2 ~1.6dB, dB - equivalent to nearly 45% more effective radiated power. Alwaysso use LMR-200240/LMR-400 for runs of several meters or bettermore. forKeep the finalfeedline run as short as practical. Important EIRP note: recovering coax loss increases EIRP — if the build is already near the 30 dBm conducted / 36 dBm EIRP ceiling, reducing feedline loss can push EIRP over the legal limit unless conducted power is correspondingly reduced.

Safety: Grounding, Lightning & Working at Height

Summit and ridge sites are high lightning-exposure locations and elevated-mast installs carry serious physical hazards. Before and during installation:

    Lightning/grounding: Bond the mast, enclosure, and the antenna's ground rod to the antennasite whengrounding transmittingsystem, and bond that ground rod to the building grounding electrode system where one exists (NEC 810.21 / 250). Install a coax surge arrestor on the feedline. Never install during approaching weather. Power-line clearance: Keep the mast's full fall-radius clear of overhead power lines — contact with lines is the leading cause of installer fatalities. Working at height: Use fall protection for any elevated mast or tower work (OSHA height triggers are 4 ft in general industry, 6 ft in construction). Tower climbing requires training, certified anchors, 100% tie-off, and a spotter. RF exposure: At amplifier power levels.levels, maintain a keep-away/safe distance per the MPE evaluation (FCC §1.1310) on rooftop/tower mounts.

    Assembly Overview

    1. Mount the MPPT controller and LiFePO4 battery in the lower half of the Fibox enclosure using DIN rail or bracket mounts.
    2. Connect the solar panel input to the MPPT controller following the manufacturer's polarity labeling. Connect the battery output terminals.
    3. WireInstall an inline fuse (sized to the wiring, typically 3-5 A) at the battery positive terminal, ahead of the MPPT load/amplifier wiring, plus a 12Vbattery disconnect/switch. The fuse must be at the battery, protecting the whole run. Never wire a LiFePO4 battery to the amplifier without overcurrent protection. Then wire a regulated output (per the amplifier's input-voltage spec) from the MPPT load terminals to the ZebraHat/Ikoka amplifier input and to a 5V step-down converter powering the T-Beam.
    4. StackConnect the ZebraHatamplifier ontoto the T-Beam GPIO headers (or connect via short SMA pigtail if usingfollowing the Ikokaamplifier module)module's documentation. Note this is the most demanding part of the build: the T-Beam's onboard SX1262/SX1276 normally feeds the board's own antenna port, so the radio's RF output must be redirected into the amplifier's RF input (the correct cable, connector, and any required board modification are specified in the amplifier module's docs — follow them). Drive the modem only to the level the PA datasheet specifies as its input (often ~10-17 dBm — the SX1262 maxes at +22 dBm and cannot itself reach 27-30 dBm). Thermal-pad the amplifier to the enclosure wall.
    5. Run LMR-200 from the amplifier RF output through a weatherproof N-type bulkhead in the enclosure wall. Terminate with an N-type connector - do not use SMA at this power level.
    6. Attach the 6 dBi fiberglass antenna to the external N-type bulkhead. Wrap the connector joint with self-amalgamating tape.
    7. Flash and configure firmware (see below), then seal the enclosure with silicone RTV on all penetrations.
    8. Mount the enclosure on the J-pipe mast with stainless U-bolts. Orient the solar panel to true south at the appropriate tilt angle for your latitude.latitude (a steeper, near-60° tilt favors winter harvest at higher latitudes).

    Firmware Configuration

    Flash the T-Beam with either Meshtastic (broader community compatibility) or MeshCore repeater firmware depending on your network's protocol stack. The T-Beam is an ESP32 board — flash it with esptool or a web flasher (it is not flashed via meshcore-cli, which only connects to an already-running node).

    • Set the modem TX power so the amplifier's CONDUCTED OUTPUT (at the coax) does not exceed 30 dBm / 1 W. The Part 15 conducted limit is independent of, and additional to, the EIRP limit. Set the T-Beam modem TX power to 27the -level the amplifier module specifies as its input (often ~10-17 dBm — check the PA datasheet); the SX1262 maxes at +22 dBm and cannot itself produce 27-30 dBmdBm. atThe amplifier provides the final ~1 W output — size the modem level.drive Theto the PA input spec, then measure the conducted output with a power meter and verify total EIRP before deployment. Operating an amplifier adds"with its gain on toptop" -of verifya total27-30 EIRPdBm againstmodem theis regulatorynot limit.legal under Part 15 and would also overdrive most PA modules.
    • Disable the OLED display after configuration to save ~roughly 10-20 mA continuously.continuously (depending on displayed content).
    • Disable Bluetooth after initial setup (reduces attack surface and saves ~5 mA).
    • Set a fixed GPS position manually once the site coordinates are known, then disable live GPS polling to save ~20 mA and extend GPS module life. Use a smartphone app on-site to capture precise coordinates before sealing.
    • Set the node role to Repeater /(or Router) and disableconfigure anythe hop-hop limit reductionappropriately that would preventso the node from forwardingforwards distant packets. (Note: the ROUTER_CLIENT role was retired in firmware 2.3.15.)
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