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LoRa

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LoRa
NameShort for "long range"
TypeChirp spread-spectrum modulation for low-power data
DeveloperSemtech, from technology bought with Cycleo in 2012
Network standard built on itLoRaWAN, from the LoRa Alliance
Signal
Spreading factorsSF7 to SF12 (SF6 in a special mode on older chips; SF5 and SF6 on newer ones)
Common bandwidths125, 250 and 500 kHz
Typical data ratesA few hundred bits per second to about 22 kbit/s at SF7 and 500 kHz
Weakest decodable signalAbout 20 dB below the in-channel noise at SF12
Ham use
Amateur bands70 cm in most countries; 33 cm in the US, Canada and some other countries in the Americas
LoRa APRS (Europe)433.775 MHz in most countries; 439.9125 MHz in the UK

LoRa, short for long range, is a radio modulation for sending small amounts of data over long distances with very little power. It comes from the semiconductor company Semtech, which bought the French startup Cycleo and its long-range modulation technology in 2012.[1] Designed for sensors and utility meters on license-free bands, cheap LoRa boards are now popular with hams for position reporting, messaging and telemetry, notably through LoRa APRS and Meshtastic.

How LoRa works

LoRa is a form of chirp spread spectrum. A chirp is a signal whose frequency sweeps steadily across the channel; Semtech describes LoRa's as wideband linear frequency-modulated pulses.[2] Two settings shape it:

  • The spreading factor (SF) sets how long each chirp lasts. Each step up doubles the time on the air and adds about 2.5 dB to the link budget, the path loss a link can tolerate. The usual range is SF7 to SF12; newer chips go down to SF5.[3]
  • The bandwidth is the width of the sweep, commonly 125, 250 or 500 kHz. Halving it halves the speed and gains almost 3 dB.[3]

The result is a direct trade of speed for range. At SF12 a receiver can decode a signal about 20 dB weaker than the noise in its own channel, whereas a conventional packet signal such as 1200-baud APRS must be stronger than the noise.[4][2] The price is a very low data rate, as Meshtastic's presets show:[3]

Preset SF Bandwidth Coding rate Data rate Link budget
Short Turbo 7 500 kHz 4/5 21.88 kbit/s 140 dB
Long Fast 11 250 kHz 4/5 1.07 kbit/s 153 dB
Long Moderate 11 125 kHz 4/8 0.34 kbit/s 156 dB

In free space each extra 6 dB doubles the possible distance, though, as with any UHF signal, real range depends mostly on antenna height and terrain.

LoRa and LoRaWAN

LoRa is only the radio signal. LoRaWAN is a network specification from the LoRa Alliance, an industry group launched by Semtech, in which battery-powered devices send short messages through gateways to a central network server.[1][5] LoRa can also be used without LoRaWAN.[6] Amateur projects such as LoRa APRS and Meshtastic send their own packet formats directly from radio to radio.

Hardware

A typical ham LoRa device is a small board with a microcontroller, often an ESP32 with Wi-Fi and Bluetooth for setup from a phone, a Semtech LoRa chip, and often a display, a GPS receiver and a battery holder. Boards come in versions for 433 MHz or for 868 and 915 MHz, so the version must match the band in use.[7]

License-free and amateur operation

United States. The 902–928 MHz band is open to unlicensed devices under Part 15 of the FCC rules, whose section 15.247 allows frequency-hopping and wideband digital systems that meet its rules up to 1 watt of transmitter output, reduced for antennas above 6 dBi gain.[8] The same frequencies form the amateur 33 cm band. Part 97 authorizes spread spectrum (SS) emissions on both 70 cm and 33 cm.[9] Most US hams treat LoRa as SS, but the FCC has not ruled on it. If LoRa were treated as an ordinary data emission instead, data on 70 cm using a code not listed in the rules would be limited to 100 kHz of bandwidth, narrower than common LoRa settings, while 33 cm has no such limit.[10] It may be used only within areas the FCC regulates or with countries that permit it, must not hide the meaning of messages, and must not interfere with other emissions.[11] Stations must identify at least every 10 minutes and at the end of each communication; LoRa systems usually do this by sending the call sign as plain text in the packets.[12] Amateur LoRa traffic must therefore be unencrypted and identified. Amateurs are secondary users of both bands, and some areas are excluded, as the articles on each band explain.

Europe. There is no amateur band near 900 MHz. License-free LoRa uses short-range device bands, including 433.05–434.79 MHz and segments around 868 MHz.[13] Limits are tight: Meshtastic's 868 MHz setting allows 500 mW at a 10 percent duty cycle, its 433 MHz setting only 10 mW.[3] The 433 MHz band lies inside the 70 cm amateur band, so in many countries licensed hams can run LoRa under their amateur license instead, subject to national rules and the band plan. Elsewhere, check the national regulator and band plan.

Ham uses

LoRa APRS

LoRa APRS carries APRS positions, messages and weather in LoRa packets instead of 1200-baud tones on 2 meters, so the two systems can't hear each other directly.[14] Trackers send positions, digipeaters relay them, and iGates pass them to APRS-IS, so LoRa stations appear on maps such as aprs.fi.[15] Popular open-source firmware by Ricardo Guzman, CA2RXU, has iGate and tracker versions for ESP32 boards, and the iGate version can also act as a digipeater.[7][15] Its frequency list gives 433.775 MHz at SF12 for Europe and much of the world, 434.855 MHz in Poland and 439.9125 MHz in the UK; in 2024 a setting for the Americas was still to be validated.[16]

Meshtastic

Meshtastic nodes relay short text messages for each other across a mesh. Most use is license-free, but in its licensed mode a node should carry the operator's call sign as its name and have encryption turned off; the command-line ham setting does both.[17]

Telemetry and remote control

The CA2RXU iGate firmware can report weather sensors and battery and supply voltages from a remote site.[7] Meshtastic's remote hardware module reads and switches pins on a distant node, though its documentation warns that wrong settings can damage the hardware.[18]

Before buying, find out what frequency and settings LoRa stations near you use. A LoRa radio can decode only signals with the same frequency, spreading factor and bandwidth, and the same network settings, so Meshtastic, LoRaWAN and LoRa APRS radios generally can't hear each other even on one channel. A 433 MHz board won't work on 868 or 915 MHz.

See also

References

  1. ↑ 1.0 1.1 The Evolution of Semtech Corporation, Semtech.
  2. ↑ 2.0 2.1 SX1272/3/6/7/8 LoRa Modem Designer's Guide (AN1200.13), Semtech, July 2013.
  3. ↑ 3.0 3.1 3.2 3.3 Radio Settings, Meshtastic documentation.
  4. ↑ LoRa FAQ, Semtech.
  5. ↑ About LoRaWAN, LoRa Alliance.
  6. ↑ What is LoRa?, Semtech.
  7. ↑ 7.0 7.1 7.2 LoRa APRS iGate, CA2RXU, GitHub.
  8. ↑ 47 CFR 15.247, Legal Information Institute.
  9. ↑ 47 CFR 97.305: Authorized emission types, eCFR.
  10. ↑ 47 CFR 97.307: Emission standards, eCFR.
  11. ↑ 47 CFR 97.311: SS emission types, eCFR.
  12. ↑ 47 CFR 97.119: Station identification, eCFR.
  13. ↑ ERC Recommendation 70-03, CEPT ECC, October 2026.
  14. ↑ LightLoRaAPRS F.A.Q., LightAPRS, GitHub.
  15. ↑ 15.0 15.1 LoRa, OARC Wiki, March 2025.
  16. ↑ Frequencies, LoRa APRS Tracker wiki, GitHub, June 2024.
  17. ↑ User Configuration, Meshtastic documentation.
  18. ↑ Remote Hardware Module, Meshtastic documentation.
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