Glossary

General Guides

The terms you will run into across these guides and in the apps, defined once, in plain language. Grouped by topic rather than alphabetically, so related ideas sit together. Terms specific to one ecosystem are labeled.

Radio basics

LoRa. The radio modulation these networks run on (from Semtech, short for "long range"). It trades speed for range and sensitivity: kilobits per second, but decodable from very weak signals. See LoRa Mesh 101.

Chirp spread spectrum. How LoRa encodes data: each symbol is a frequency sweep (a chirp). This is what lets a receiver pick signals out from below the background noise.

Spreading factor (SF7 to SF12). How slowly and deliberately the radio talks. Each step up roughly doubles airtime and adds range. Both ends must match to hear each other.

Bandwidth. The width of the radio channel, typically 125, 250, or 500 kHz. Wider is faster but less sensitive. Both ends must match.

Coding rate. How much error-correction data is added, written 4/5 through 4/8. More correction survives worse links but costs airtime.

Time on air (airtime). How long a single transmission physically occupies the channel. Drives legal limits, congestion, and battery. See the Airtime Calculator.

Duty cycle. A legal cap on what fraction of each hour you may transmit, used in EU bands (1% means 36 seconds per hour). See Frequencies & Regions.

Dwell time. A legal cap on the length of a single transmission instead of an hourly budget; the US frequency-hopping rule is 400 ms.

ISM / SRD band. The license-free radio bands these devices use (902-928 MHz in the US, 863-870 MHz in Europe). No exam or callsign, in exchange for power limits and tolerating interference.

dBm. Absolute radio power on a logarithmic scale: 0 dBm is 1 milliwatt, +30 dBm is 1 watt. Every 3 dB doubles the power.

dBi. Antenna gain relative to a theoretical antenna that radiates equally in all directions. Gain does not add power; it reshapes where the power goes. See Antennas & RF Basics.

EIRP / ERP. The effective power actually radiated in the strongest direction, transmitter power plus antenna gain minus losses. This is usually what regulations limit, not raw transmitter power.

RSSI. Received signal strength, in dBm. Always negative in practice; closer to zero is stronger (-60 is strong, -120 is very weak).

SNR. Signal-to-noise ratio: how far the signal sits above (or below) the background noise, in dB. LoRa can decode at negative SNR, which is its party trick.

Noise floor. The background RF level from everything else: electronics, other transmitters, the universe. Your signal competes with it.

Line of sight. An unobstructed straight path between two antennas. At these frequencies it is most of what determines range. See Range Expectations.

Fresnel zone. The football-shaped region around the line of sight that also needs to be mostly clear. Tens of meters thick at mid-path on long links, which is why "I can see it" is not the same as "I can reach it".

Low data rate optimization (LDRO). A radio setting that stabilizes very slow, high spreading factor transmissions. Firmware normally handles it for you (on at SF11/SF12 with 125 kHz bandwidth).

Mesh concepts

Node. Any single radio device participating in the network.

Mesh. A network where messages reach their destination by hopping between nodes, with no towers or central infrastructure.

Hop. One relay step: a message passing through one intermediate node.

Hop limit. The maximum number of relay steps a packet gets before it is dropped. Keeps messages from circulating forever.

Flooding. A relay strategy where nodes rebroadcast packets they have not seen before. Meshtastic uses a managed version of this; MeshCore floods for discovery but routes direct messages along learned paths.

Packet. One radio transmission: your message plus the protocol wrapping (addresses, IDs, hop counter).

Payload. The useful data inside a packet, as opposed to the protocol overhead around it.

Channel. A named group conversation protected by a shared encryption key. Everyone holding the key is in the channel.

PSK (pre-shared key). The secret key that encrypts a channel, usually distributed as a QR code or URL. A channel is exactly as private as its key handling.

Store-and-forward. Holding messages for nodes that are offline and delivering them when they reconnect. In MeshCore this is what room servers do; Meshtastic channels do not do this by default.

Telemetry. The housekeeping data nodes broadcast periodically: position, battery, environment readings.

Hardware

ESP32. A microcontroller family with WiFi and Bluetooth. Cheap and capable, but power hungry: battery life in days. See Hardware.

nRF52840. A microcontroller with Bluetooth LE only and very low idle draw: battery life in weeks. The default answer for battery and solar nodes.

SX1262. The Semtech LoRa radio chip in most current boards, transmitting up to +22 dBm.

UF2 bootloader. The drag-and-drop flashing method on nRF52 boards: double-tap reset, the board mounts as a USB drive, copy the firmware file on.

U.FL / IPEX. The tiny snap-on antenna connector on many boards. Fragile and rated for few connect cycles; use a pigtail rather than swapping antennas on it.

SMA / RP-SMA. The threaded antenna connectors. Two incompatible genders of the same idea; check which one your board and antenna actually have before ordering.

MeshCore terms

Companion. Your personal node, paired to the phone app (or a computer). Companions do not relay traffic.

Repeater. A dedicated relay node, administered remotely over the mesh. In MeshCore, repeaters do the forwarding that other nodes do not.

Room server. A shared message board node with store-and-forward: members get held messages when they reconnect. Holds a fixed-size buffer, not an archive.

Advert. A signed broadcast announcing a node: name, public key, optionally location. How nodes discover each other and how the mesh learns paths.

Path. The learned route (through specific repeaters) that a MeshCore direct message follows, instead of flooding the whole mesh.

Hashtag channel. A channel joined by name: enter the same #name, land on the same channel. As private as the name is obscure.

Meshtastic terms

Modem preset. A named bundle of radio settings (spreading factor, bandwidth, coding rate). LongFast is the default nearly every public mesh runs.

Primary / secondary channels. A node holds one primary channel (the default one is effectively public) plus optional secondary channels, so the public mesh and private groups coexist on one node.

Node roles. How a node participates: CLIENT (normal, relays), ROUTER (rebroadcast priority, for well-placed infrastructure only), CLIENT_MUTE (never relays).

MQTT. An optional bridge between the mesh and an internet server. Links distant meshes and feeds the public maps, and is also why "nodes" sometimes appear from thousands of km away.

NodeDB. The list of every node your device has heard about. Entries linger, so last-heard time matters more than presence in the list.