Working on an off-grid, jam-resistant mesh comms device for when cell networks go down — feedback wanted
Open-Source Tactical Mesh Radio Node (LoRa/LR-FHSS + BLE, ESP32-S3)
I'm designing a pocket-sized mesh communicator built around the Semtech LR1121, meant for off-grid/contested-RF environments where cell and Wi-Fi aren't options.
Core idea: one small device, three operating modes:
- USB Modem — plug into a laptop/tablet
- BT Modem — pair with a phone via BLE 5.0
- Autonomous Relay — standalone mesh repeater, no host needed
RF layer (LR1121):
- Dual-band sub-GHz + 2.4GHz, hardware LR-FHSS for jam resistance (~3km range even under active jamming), plus GFSK for short-hop mesh relaying
- Adaptive channel activity detection to keep relay power draw under 10mA
- External PA option pushes LoS range to 15km in "hidden" (SF12) mode
Anti-jamming (multi-layer EW resistance): this is one of the core design pillars, with a stacked defense model:
- Waveform layer — adaptive spreading factor (up to SF12 for +15dB processing gain against broadband jammers), hardware frequency hopping across 335 channels at ~100µs hop rate (fast enough that even "follow-me" jammers can't react in time), and sub-5ms burst transmissions to dodge reactive jammers
- Timing/power masking — randomized TX intervals, power control, and padded/encrypted packet sizes to reduce fingerprinting
- Frequency agility — different countermeasures automatically selected depending on jammer type detected (broadband, spot, follow-me, reactive, or deceptive/spoofed preambles)
- Network resilience — per-link FEC and adaptive retransmission timing
- Traffic analysis protection — dummy cover traffic and fixed packet sizing so an observer can't tell when real messages are being sent, plus cryptographic verification to reject spoofed/deceptive jamming packets
Three tactical RF profiles, switchable depending on the threat environment:
- HIDDEN — low probability of intercept/detection: minimal power, no GFSK, heavy timing jitter + cover traffic, text-only voice
- NORMAL — balanced smart spectrum sensing, adaptive data rate, mesh relay available
- OVERRIDE ("unrestricted mode") — max aggression setting for emergencies: full hardware frequency-hopping + burst mode, max transmit power (up to +30dBm with external PA), TDMA micro-slots instead of listen-before-talk. Duty cycle automatically throttles down in hot ambient conditions (thermal + regulatory safety net) so the radio doesn't cook itself or the PA even when running "wide open."
Security: identity keys and cluster master key live in a dedicated secure element (ATECC608B) — physically tamper-resistant, keys get destroyed if someone tries to probe the chip. There's also a "panic beacon" that broadcasts a distress signal before self-destructing keys if the case is opened.
Time sync: implements the Flooding Time Synchronization Protocol (FTSP) to keep frequency-hopping nodes aligned across a mesh without needing GPS on every node.
Voice: three modes — push-to-talk (Codec2, <400ms latency), voice messages, and a "text voice" mode that does speech-to-text → compressed text over the mesh → text-to-speech on the receiving end (useful for very low-bandwidth/high-latency links).
Companion app: Flutter, cross-platform (Android/iOS/Windows/Linux/macOS), plus an ATAK plugin for tactical mapping integration. Networking runs on Reticulum (RNS).
