SDRTrunk Setup Guide: P25 Trunking with RTL-SDR V4

Hardware Shopping List

For P25 Phase II, the reliable setup is:

• Two RTL-SDR Blog V4 dongles — one for the control channel, one for voice. The V4's 1 PPM TCXO is essential; older no-TCXO dongles drift and lose the control channel. See our V4 review for why this is the right dongle.
• A powered USB 3.0 hub — at least 5V/3A output, ideally one with individual port power. Anker, Sabrent, and UGREEN all make reliable models for about $25.
• A wideband antenna — a discone like the Tram 1411 is the standard choice because it covers VHF, UHF, and 700/800 MHz bands with a single element.
• Two short SMA-to-coax jumpers (or a splitter if you only want one antenna) — RTL-SDR V4s use SMA female; most discones come with PL-259 (UHF) connectors, so you'll need adapters.
• A modern PC with Java 21 — Windows, Linux, or macOS all work. At least 8 GB of RAM.

Total budget: about $130 for the full kit if you already own a PC. That's less than a used scanner and more capable for P25 trunking.

Step 1: Install Java and SDRTrunk

1. Download Java 21 — grab the Adoptium Eclipse Temurin JDK 21 (or newer LTS) for your OS. SDRTrunk requires Java 21 or later.
2. Download SDRTrunk — from GitHub at DSheirer/sdrtrunk. Grab the latest release ZIP for your platform (Windows, Linux x64, macOS).
3. Extract and run — on Windows, run bin/sdr-trunk.bat. On Linux/macOS, bin/sdr-trunk. The GUI opens on first launch.
4. Install RTL-SDR drivers — on Windows, use Zadig to swap the default USB driver for WinUSB on each RTL-SDR. Make sure you're using the RTL-SDR Blog V4 driver branch; older R820T2-only builds won't tune HF on a V4.

Step 2: Plug In the Hardware

1. Connect the powered USB hub to your PC with its included USB 3.0 cable.
2. Plug each RTL-SDR V4 into the powered hub (not directly into the PC).
3. Attach short SMA jumpers from each V4 to the antenna feedline. If you're using one antenna feeding two dongles, add a 2-way splitter rated for 1 MHz to 2 GHz.
4. Connect the Tram 1411 (or your chosen wideband antenna) to the feedline.
5. In SDRTrunk, open Tuner → the two V4s should appear. Name them "Control" and "Voice" to keep track.

Step 3: Import Your System from RadioReference

SDRTrunk doesn't come preloaded with US public safety systems. You pull them from RadioReference.com (a RadioReference Premium subscription at $15/year makes this much easier). In SDRTrunk:

1. Go to Playlist Editor → Import.
2. Choose Import RadioReference System and enter your credentials.
3. Search for your agency's trunked system (for example, a statewide P25 system) and import it.
4. SDRTrunk will pre-populate the control channels, site frequencies, and known talkgroups.

If you don't subscribe to RadioReference, you can manually enter the system information — system ID, WACN, control channel frequency, and talkgroups. It's tedious but free.

Step 4: Configure the Channels

In the playlist editor, create two channels:

• Control channel: set the decoder to P25 Phase 1 Control. Assign your first V4 ("Control") as the tuner. Set center frequency to the system's primary control channel (for example, 773.44375 MHz for a Phase II system).
• Voice channel: set the decoder to P25 Phase 2 (or Phase 1 if it's a Phase 1 system). Assign your second V4 ("Voice") as the tuner. SDRTrunk will automatically tune this dongle to voice channels as the control channel announces them.

Start both channels. Within 10–30 seconds you should see the control channel lock and status changing to "Sync" or similar.

Step 5: Tune Gain and Verify

Each RTL-SDR has a tuner gain setting. Start around 28–32 dB. If you see a lot of decode errors, try lowering gain first; if the signal is weak, raise it. Avoid maxing gain — it adds more noise than signal in most urban environments.

In the Now Playing tab, you should see call activity. Each call will show:

• Source radio ID and talkgroup
• BER (bit error rate) — under 3% is healthy
• Encryption status — if you see AES-256 or DES-OFB, that call is encrypted and won't produce audio
• Duration and signal strength

Common Problems and Fixes

Alternatives If SDRTrunk Isn't a Fit

SDRTrunk is the best free trunk-tracking software, but not the only option. For comparison:

• DSD+ Fastlane — paid, Windows-only, excellent Phase II decoder. Often paired with SDR# for the front-end. See our SDR software comparison.
• OP25 — free, Linux-focused, command-line trunking decoder with a GUI fork. Steeper learning curve.
• Unitrunker 2 — follows analog and some digital trunked systems. Less maintained than SDRTrunk.
• A dedicated scanner — see our RTL-SDR vs dedicated scanner comparison for when the hardware solution is simpler.

Frequently Asked Questions