RF & Wireless Glossary

Received Signal Strength Indicator. A relative measure of incoming RF power at the antenna, expressed in negative dBm (e.g. -60 dBm is strong, -115 dBm is near the sensitivity limit).

Signal-to-Noise Ratio. The ratio of received signal power to background thermal noise in decibels (dB). While FSK needs a positive SNR (+4 to +10 dB) to decode, LoRa can pull packets out from deep inside the noise floor down to -20 dB.

Accounting of all gains and losses from transmitter to receiver: TX power + TX antenna gain - path loss - cable loss + RX antenna gain. If the remaining power beats receiver sensitivity, the link holds.

Voltage Standing Wave Ratio. Measures how well an antenna is matched to 50 ohms. An SWR of 1.1:1 to 1.5:1 means power radiates outward; high SWR reflects energy back into the radio output stage as heat.

Equivalent Isotropically Radiated Power. The total power an isotropic antenna would need to emit to match the strongest direction of your real antenna. Regulators cap EIRP to prevent overpower.

On-Off Keying / Amplitude Shift Keying. The simplest modulation: pulsing carrier on for 1 and off for 0. Cheap to build, but easily blinded by electrical noise.

Frequency Shift Keying. Shifting carrier between two frequencies. Gaussian filtering (GFSK) smooths the frequency transitions to keep power inside the channel.

The modulation behind LoRa. Sweeps carrier frequency continuously across a bandwidth band (up-chirp or down-chirp). Resistant to fading, multipath reflection, and Doppler shift.

Low Noise Amplifier. The first stage inside the receiver that boosts weak incoming signals without drowning them in internal amplifier noise.

Power Amplifier. The output stage that boosts the modulated signal up to transmit power (e.g., +14 dBm or +22 dBm).

The number of chirps used to encode each symbol (calculated as 2^SF chirps per symbol, from SF7 to SF12). SF7 is fast and saves battery; SF12 takes 32 times longer on the air but digs 15 dB deeper into noise.

The exact duration in milliseconds a radio spends transmitting a packet. High spreading factors and larger payloads increase airtime, which drains battery and increases collision risk.

Forward Error Correction (FEC) overhead added to packets (4/5, 4/6, 4/7, or 4/8). The receiver uses these extra bits to reconstruct corrupted bytes on the fly without asking for retransmission.

An open-source, decentralized packet mesh project. Nodes route messages through each other automatically over sub-1GHz LoRa using managed flood routing without needing cell towers or internet.

A lightweight, structured LoRa mesh networking protocol. Replaces broadcast flooding with role-based routing (Clients, Repeaters, and Room Servers) to prevent channel saturation in dense networks.

A persistent mailbox node in MeshCore that caches channel messages and sensor logs, allowing offline clients to synchronize missed traffic once back in RF range.

A mesh routing algorithm where every node rebroadcasts received packets up to a hop limit. Simple and zero-configuration, but prone to channel congestion in high-density areas.

A point-to-multipoint star network protocol. Remote nodes send packets to central multi-channel gateways, which forward data over IP to a central network server like ChirpStack.

A burst of alternating bits or unmodulated chirps sent first so the receiver hardware can wake up, tune its gain, and lock clock timing.

A distinctive bit pattern right after the preamble. The radio matches this to know where real payload begins and filter out transmissions from other networks (e.g. 0x12 for private/Meshtastic, 0x34 for LoRaWAN).

A digital line code where each bit is represented by a transition (e.g. low-to-high for 0, high-to-low for 1). Guarantees regular voltage transitions for clock recovery in OOK and FSK sensor transmissions.

An IEEE 802.11 management frame used for explicit protocol actions. ESP-NOW uses vendor-specific Action Frames (Category 127) to transmit connectionless payloads without associating to an access point.

Cyclic Redundancy Check. A checksum appended to the packet. The receiver verifies it; if even one bit flipped in flight, the hardware discards the frame.

The maximum percentage of time a radio is legally allowed to transmit within an hour. In European 868 MHz sub-bands, strict 0.1% or 1% limits require polite channel sharing.

A dedicated sub-1GHz home automation standard operating at 908.4/916.0 MHz (US) and 868.4 MHz (EU). Operates with zero interference from 2.4 GHz Wi-Fi using 9.6/40/100 kbps FSK mesh routing.

A 1-mile direct star-topology extension of Z-Wave operating at 912 MHz / 920 MHz (US) up to +30 dBm (1 W). Expands network capacity from 232 nodes up to 4,000 nodes without intermediate mesh repeaters.

Security 2 framework for Z-Wave using Diffie-Hellman elliptic curve key exchange and AES-128 encryption. Eliminates the man-in-the-middle pairing vulnerabilities of legacy S0 security.

Mandatory radar-detection mechanism on 5 GHz UNII-2 channels (5250–5725 MHz). If a radio detects weather or military radar pulses, it must instantly silence transmission and vacate the channel for 60 seconds.

Cloud database coordination required by the FCC for Standard Power (outdoor) 6 GHz Wi-Fi 6E/7. Radios report their GPS coordinates and antenna height to receive allowed transmit power levels that protect licensed satellite uplinks.

Unlicensed National Information Infrastructure bands in 5 GHz spectrum (UNII-1, UNII-2A, UNII-2C, UNII-3). Each tier has different transmit power caps, indoor/outdoor restrictions, and radar rules.

Espressif connectionless 2.4 GHz protocol using vendor-specific Wi-Fi action frames. Enables low-latency (<5 ms) peer-to-peer packet transfer between ESP32/ESP8266 devices without connecting to a Wi-Fi router.

Title 47 CFR Part 15 federal regulations governing unlicensed intentional, unintentional, and incidental RF radiators. Governs power limits, spurious emissions, and band edges for Wi-Fi, LoRa, and sub-1GHz devices.

The statutory mechanism allowing individuals to deploy and operate compliant RF equipment without applying for a personal station license or callsign, because the hardware is pre-certified at the factory.

Equipment authorization granted to a self-contained RF sub-assembly (e.g. ESP32-WROOM, RAK LoRa modules) with integrated shielding and firmware controls. Allows builders to design custom carrier boards without full transmitter re-certification.

Receiver state that passes all ambient radio packets to the host processor for passive diagnostics and channel auditing, regardless of destination MAC address. Strictly passive listening without network association.

An IEEE 802.11 management broadcast transmitted roughly 10 times per second by Wi-Fi routers. Auditing beacons allows passive measurement of channel congestion, signal strength (RSSI), and clear frequency slots.

The engineering discipline of measuring ambient RF noise floors, channel utilization, and signal propagation across a physical area to optimize antenna placement and channel selection before deploying wireless nodes.