Trunked & Public Safety
SDRTrunk, Trunk-Recorder, OP25, DSD+ — listen to P25 / DMR / NXDN trunked radio systems.
Public-safety radio in 2026 is mostly trunked (a control channel directs talkers to dynamically allocated voice channels) and increasingly encrypted. The decoders here let you follow unencrypted systems — almost all small-town / rural police, fire, EMS, public works, and amateur trunked systems are still in the clear. Encrypted P25 Phase 2 systems (most large-city PD) are not breakable with these tools (and you shouldn't try). Cross-link with SDR Receivers and SDR Software for the front-end. Legality varies by state / country — listening is generally legal in the US (federally) but recording or repeating is restricted. Look up your jurisdiction.
Multi-channel trunking decoders
- ★ SDRTrunk — Java, cross-platform, GUI + headless modes. Decodes P25 Phase 1, P25 Phase 2, DMR, NXDN, MPT-1327, Fleetsync, LTR-Net. Streams to Broadcastify / OpenMHz, records to MP3. Single dongle covers a whole control channel + multiple voice channels via channelized SDR. The 2026 default for hobbyists. GPLv3.
- ★ Trunk-Recorder — Linux / macOS, headless, C++. Multi-system, multi-control-channel, scales to large county-wide systems. Used by half the OpenMHz / Broadcastify Calls feeders. Outputs WAV / MP3 with metadata; integrates with rdio-scanner for web UI. GPLv3. The default if you want to record everything 24/7.
- boatbod's OP25 — Python; P25 Phase 1 and Phase 2; runs lean on a Pi; older but still maintained for simple P25 systems. GPL.
- OP25 (osmocom) — original / upstream; less active than boatbod's fork.
Single-channel voice decoders
- DSD-FME — open-source DSD (Digital Speech Decoder) fork; decodes P25, DMR, NXDN, dPMR, ProVoice from a sound card / audio pipe. GPL. The free CLI alternative to DSDPlus.
- DSDPlus — Windows; closed; freeware basic version. Decodes P25 / DMR / NXDN / X2-TDMA from audio. Better voice quality than DSD-FME because of paid AMBE codec licensing.
- DSDPlus Fastlane — paid (~$100); maintained subscription; the only legal way to decode modern AMBE+2 voice on Windows. Closed.
- Boatbod-OP25 is more capable than DSD-FME for P25 specifically.
Web UIs / management
- ★ rdio-scanner — web UI for Trunk-Recorder; talkgroup browser, live audio playback, recordings archive. The standard "dispatcher's screen" for self-hosted setups. MIT.
- liquidsoap-based archives — for recording / streaming downstream.
Streaming networks
- ★ Broadcastify — the dominant public-safety streaming network. Closed; pay for premium calls archive. Most active feeders use Trunk-Recorder + the Broadcastify Calls API.
- OpenMHz — open-philosophy alternative to Broadcastify; takes Trunk-Recorder feeds. Free for listeners and feeders.
- RadioReference — see Frequency Databases below; same parent company as Broadcastify.
Frequency / system databases
- ★ RadioReference Database (radioreference.com) — the canonical North American P25 / DMR / conventional system database. Premium subscription ~$15/yr required for talkgroup downloads in machine-readable format; free web browsing. Closed but de facto.
- SignalIdentificationGuide.org / sigidwiki — what a signal looks like in a waterfall; identification reference. Free, wiki.
- FCC ULS — US Federal Communications Commission license database; open data. Find the licensee for any FCC-licensed transmitter.
- OFW (Ofcom UK), Industry Canada Spectrum Direct, ACMA (Australia) — country-specific equivalents.
- ScannerMaster — paid scanner programming database / cables / hardware.
Hardware
- RTL-SDR Blog v4 + a real VHF/UHF antenna — adequate for one or two control-channel systems.
- Airspy R2 / SDRplay RSPdx-R2 — better dynamic range; recommended if a strong pager / paging system is nearby.
- Multi-dongle setups — Trunk-Recorder loves multiple cheap RTL-SDRs (one per control channel + one per voice frequency block). A USB hub + 4–8 RTL-SDRs on a Pi is a common setup.
- GPS-disciplined oscillator (GPSDO) — mostly unnecessary for trunking but helps if you're stitching multi-dongle setups across a wide-band system.
- Scanner radios as alternative — Uniden SDS100/200, Whistler TRX-1/2 — turnkey hardware scanners with the codec keys baked in, cost $400–$700, no Pi or computer needed.
Practical guidance
- Identify the system first. RadioReference will tell you if your county runs P25 Phase 1 (analog FDMA, easy), P25 Phase 2 (TDMA, harder, AMBE+2), DMR Tier III (also TDMA), or encrypted Phase 2 / DMR with AES. Phase 2 + encryption is undecodable with these tools.
- Control channel first, voice channels follow. Tune the control channel only; the decoder will follow voice frequencies as the system allocates them.
- Bandwidth. A typical P25 Phase 1 trunked system uses 5 MHz of spectrum total — within the bandwidth of any modern SDR. Trunk-Recorder will channelize the IQ stream and decode multiple talkgroups simultaneously.
- Talkgroup vs frequency. Trunked systems route by talkgroup ID not frequency; configure tags from RadioReference so logs make sense.
- Encryption is rising. Federal agencies, large-city PD/Fire/EMS are increasingly encrypted; rural systems usually aren't. Don't try to decrypt — illegal under CALEA / Computer Fraud and Abuse Act in the US, and the keys are AES-256.
- AMBE codec licensing. AMBE+2 is patented (DVSI); free decoders use either the patent-expired AMBE (Phase 1) directly, or the mbelib library which is in legal grey territory. DSDPlus Fastlane pays the license; DSD-FME and SDRTrunk use mbelib.
License / pricing notes
- SDRTrunk / Trunk-Recorder / OP25 / DSD-FME / rdio-scanner — FOSS (GPL / MIT).
- DSDPlus Fastlane — closed, paid (~$100/yr-ish).
- Broadcastify — closed, free listeners, paid premium.
- OpenMHz — open community, free.
- RadioReference — paid subscription for full database access.
- mbelib — debated legal status (DVSI claims patent); used by FOSS decoders pragmatically.
Pick this if…
- Default GUI scanner, hobbyist: SDRTrunk.
- Default 24/7 recorder for a county system: Trunk-Recorder + rdio-scanner.
- Just one P25 system on a Pi: boatbod's OP25.
- Best voice quality (Windows, paid): DSDPlus Fastlane.
- No computer at all: Uniden SDS100 hardware scanner.
- System lookup: RadioReference.com (worth the subscription).
- Feed the community: OpenMHz (open) or Broadcastify (more visibility).