Glossary

Plain-language definitions of technical terms used throughout this guide.

A

Amateur radio— also: ham radio, amateur radio operator, ham
Amateur radio (also called ham radio) is a globally licensed radio service regulated by national telecommunications authorities in each country, operating under international agreements administered by the ITU. Licensed operators — called hams — can use a wide range of frequencies and power levels for personal communication, experimentation, and public service. Amateur radio operators provide a significant share of emergency communication support worldwide. Licensing requires a technical exam in most countries.Learn more →
Antenna— also: antennas
An antenna is the interface between your radio and the air. The stock antenna supplied with a handheld radio is a compromise — a better antenna, especially one mounted at height, can multiply effective range several times over with no increase in transmit power. Key antenna properties: gain (how much it focuses energy in a useful direction, measured in dBi), polarisation (vertical antennas work best with other vertical antennas), and resonant frequency (an antenna tuned for the wrong frequency wastes power). For fixed installations, an outdoor antenna on a roof or mast is one of the highest-value upgrades.
APRS— also: Automatic Packet Reporting System
APRS (Automatic Packet Reporting System) is a digital protocol used on amateur radio frequencies to broadcast real-time data: GPS positions, weather station readings, and short text messages. Data from APRS-equipped stations is automatically relayed by digipeaters and uploaded to the internet via iGates, making positions visible on public maps like aprs.fi. APRS is widely used by amateur radio operators for tracking field teams during disasters. It requires a ham radio licence to transmit.Learn more →
AREDN
AREDN (Amateur Radio Emergency Data Network) is a project that repurposes off-the-shelf WiFi hardware (primarily Ubiquiti devices) to operate on amateur radio frequencies. The result is a high-bandwidth mesh network that can carry voice, video, and data — far more capacity than LoRa-based systems. Operating on amateur radio frequencies requires a license but allows higher power and more flexibility than unlicensed WiFi. AREDN networks are deployed by amateur radio clubs around the world specifically for emergency communication.Learn more →

B

Backhaul— also: backhaul link
Backhaul is the connection between a local access network (the part users connect to) and the broader internet or wider network. In a city, the backhaul might be fiber cables running from cell towers to carrier switching centers. In a resilient communication plan, backhaul is typically the weakest point — it concentrates traffic into a small number of physical paths that can be cut by a single disaster. Satellite links (like Starlink) are increasingly used as backup backhaul because they are independent of terrestrial infrastructure.

C

CERT
CERT (Community Emergency Response Team) is a program that trains community members in basic disaster response skills: fire safety, light search and rescue, team organization, and disaster medical operations. CERT teams work alongside professional emergency services, not in place of them. The program originated in Los Angeles and is now active in many countries under different names. CERT teams are a natural home for neighborhood communication networks.Learn more →
Channel— also: channels, radio channel
In radio, a channel is a stored frequency configuration — often including a transmit frequency, receive frequency, and any required tones (like CTCSS). Programmable radios store dozens of channels so operators can switch with a knob rather than entering numbers under pressure. In Meshtastic, a channel is a named, encrypted communication group — closer to a group chat than a radio frequency. Standardising channel assignments across a team (Ch 1 = primary, Ch 2 = logistics, Ch 3 = emergency) is a core operational practice.
Circumvention
Circumvention refers to tools and methods used to bypass internet filtering, censorship, or surveillance. This includes VPNs (Virtual Private Networks), the Tor network, and specialized tools like Psiphon and Lantern. Circumvention is distinct from offline communication — it assumes some internet connectivity exists but is censored, whereas mesh and radio techniques address scenarios where connectivity is absent entirely.
CTCSS— also: PL tone, PL tones, tone squelch, CTCSS tone
CTCSS (Continuous Tone-Coded Squelch System) — also called PL tones or privacy tones — is a system where a radio transmits a low-frequency tone below the audible range along with its voice signal. A receiving radio only opens its squelch (lets audio through) if it detects the matching tone. This prevents your radio from playing every transmission on a busy shared frequency, only activating when someone from your group transmits. CTCSS does not encrypt or hide communications — anyone scanning the frequency can still hear you — it only filters which transmissions open your speaker.

F

Firmware— also: flash, flashing
Firmware is low-level software embedded in hardware devices. Unlike apps on a phone, firmware runs directly on the device's processor with no operating system underneath. Meshtastic, AREDN, and many other resilient communication tools are distributed as firmware that you load (flash) onto compatible hardware. Keeping firmware up to date is important for security and new features. Flashing firmware incorrectly can make a device unresponsive — always follow the official instructions.
Frequency— also: frequencies
Radio frequency is measured in hertz (Hz) — cycles per second. Practical radio uses megahertz (MHz, millions of cycles) and gigahertz (GHz, billions of cycles). Lower frequencies (HF, below 30 MHz) can travel thousands of kilometers by bouncing off the ionosphere. Higher frequencies (VHF/UHF, 30 MHz–3 GHz) travel in straight lines and are blocked by terrain, but carry more data. WiFi and Meshtastic operate in the GHz range. Every frequency or band has rules about who can use it, at what power, and for what purpose.Learn more →

G

Gateway— also: gateways, internet gateway
A gateway bridges two different network types. In Meshtastic, an MQTT gateway connects the local LoRa mesh to the internet, allowing messages to reach nodes beyond radio range when connectivity is available. In AREDN, a gateway node connects the high-speed WiFi mesh to the broader internet. In Winlink, a radio gateway station connects HF or VHF packet radio to the email network. Gateways are single points of failure — a resilient network design minimises dependence on any single gateway and has fallback paths when gateways are offline.
GMRS
GMRS (General Mobile Radio Service) is a radio service licensed by the US FCC for short-range personal and family communication. A single license covers an entire household and is valid for 10 years. No technical exam is required — only a fee and an application. GMRS radios are widely available and inexpensive. Outside the United States, equivalent services exist under different names and regulatory bodies — PMR446 in Europe, for example.Learn more →

H

HF / VHF / UHF— also: HF, VHF, UHF, high frequency, very high frequency, ultra high frequency
HF (High Frequency, 3–30 MHz) radio waves can bounce off the ionosphere and travel thousands of kilometers — useful for regional or international communication when all other infrastructure is down. VHF (Very High Frequency, 30–300 MHz) and UHF (Ultra High Frequency, 300 MHz–3 GHz) travel in straight lines and are limited by terrain and curvature of the earth, typically to tens of kilometers. Most handheld radios, repeaters, and GMRS operate in VHF or UHF. HF requires larger antennas and more complex equipment but is the backbone of long-haul emergency radio.Learn more →

I

Internet shutdown
Internet shutdowns are deliberate disruptions of internet or mobile data services, typically ordered by governments. They can be total blackouts (all connectivity cut) or partial (specific services like social media blocked). They are increasingly common during elections, protests, and conflicts. Local mesh networks, LoRa radio, satellite services, and circumvention tools can all provide communication paths that bypass or survive these shutdowns to varying degrees.Learn more →

L

Licensed spectrum— also: licensed band, licensed frequencies, unlicensed spectrum, unlicensed band
Governments allocate radio spectrum through licensing. Licensed bands — like amateur radio (ham) and GMRS in the US — require a licence, but in return users get legal protection from interference and often higher power limits. Unlicensed bands — like the 2.4 GHz and 5 GHz bands used by WiFi, and the 915 MHz / 868 MHz bands used by Meshtastic — require no licence but are shared by many users with no interference protection. For resilient communication, licensed bands are generally preferable: higher power, less congestion, and legal authority to operate.
LoRa— also: LoRa radio
LoRa (Long Range) is a radio modulation technique developed by Semtech. It trades data speed for range and power efficiency — a LoRa device can transmit several kilometers on a small battery, but can only send short, slow messages. This makes it well-suited for text messaging, position tracking, and sensor data in off-grid scenarios. Meshtastic uses LoRa as its underlying radio technology.Learn more →

M

Mesh network— also: mesh networking, mesh networks, mesh
In a mesh network, devices (called nodes) communicate directly with each other and forward messages on behalf of other nodes. If one node fails, traffic automatically routes around it. This makes mesh networks far more resilient than hub-and-spoke designs, where failure of the central hub brings the whole network down. Mesh networking is used in both WiFi systems (like AREDN) and long-range radio systems (like Meshtastic).Learn more →
Meshtastic
Meshtastic is open-source firmware that runs on small, low-cost LoRa radio modules. Devices running Meshtastic form an automatic mesh network — each device extends the range of the others by relaying messages. Users communicate via a smartphone app connected to the device over Bluetooth. The system requires no internet, no cellular network, and no central server. It is well-suited for neighborhood-scale text messaging and position sharing during emergencies.Learn more →

N

Net control
In amateur radio and emergency communication, a 'net' is a scheduled gathering of radio operators on a shared frequency. Net control is the station that runs the session — calling for check-ins, acknowledging stations, and managing traffic. Rotating net control among team members ensures more people are trained to run a net independently when needed.
Node— also: nodes
A node is the basic building block of any network. In a mesh network, each node both uses the network and helps extend it by relaying traffic for other nodes. In practice, a node might be a Meshtastic device clipped to a backpack, a WiFi router mounted on a rooftop, or a repeater on a hilltop.

P

Power resilience
Power resilience means ensuring your communication equipment has a power source that survives the same events that cut communications — storms that knock out the grid, earthquakes that destroy substations, or intentional shutdowns. Common approaches include battery banks (hours to days of runtime), solar panels with charge controllers (indefinite runtime in sufficient sun), and generators (requires fuel). The most resilient systems use multiple power sources and know the power budget of each device.
PSK— also: pre-shared key
A Pre-Shared Key (PSK) is a secret value that is distributed to authorized devices or users before communication begins. In Meshtastic, setting a PSK on a channel means only devices that know the key can read the messages — others can hear the radio signals but cannot decode them. PSKs must be distributed securely (in person, not over the network being secured) before an emergency.

R

Repeater— also: repeaters
A repeater listens on one frequency and simultaneously re-transmits what it hears on another. Because repeaters are usually located at elevation (hilltops, tall buildings, towers), they can serve a much wider area than a handheld radio can reach on its own. Many amateur radio clubs maintain repeaters that remain operational during disasters. A repeater is a single point of failure — if it goes offline, everyone relying on it loses coverage.Learn more →

S

Simplex
Simplex means two radios communicate directly, on the same frequency, without going through a repeater or any intermediate infrastructure. Range is limited by the power and antenna of the radios involved and the terrain between them, but simplex is the most resilient mode — it works even when all repeaters and infrastructure are offline. Most playbooks recommend a designated simplex frequency as a fallback when other communication paths fail.