SDRTrunk Setup Guide: P25 Trunking with RTL-SDR

Hardware Shopping List

For P25 Phase II, the reliable setup is:

• One or two RTL-SDR Blog V3 dongles. One dongle covers about 2.4 MHz; if your site's frequencies span more, add a second so SDRTrunk has room for voice channels. A TCXO matters; no-TCXO dongles drift and lose the control channel. The genuine RTL-SDR Blog V3 ($37.95) has one and covers the VHF, UHF and 700/800 MHz bands P25 uses. We used to recommend the RTL-SDR Blog V4, but it was discontinued in May 2026; RTL-SDR Blog says the V3 stays in production. A V4 you already own works here too; see RTL-SDR Blog's V4 users guide for its driver requirements.
• A powered USB 3.0 hub — at least 5V/3A output, ideally one with individual port power.
• A wideband antenna — a discone like the Tram 1411 ($82.99) 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 Blog dongles use SMA female; many discones use UHF-series (SO-239/PL-259) connectors, so you'll likely need adapters.
• A 64-bit PC: Windows, Linux or macOS (x86 or ARM). The project prefers a 4-core CPU and 8 GB of RAM. No separate Java install needed; releases bundle a runtime.

Prices move, so check the current price on each part; the dongles and antenna above show today's.

Step 1: Install Java and SDRTrunk

1. Skip the Java install: SDRTrunk releases include a complete Java runtime (OpenJDK 23 in v0.6.1), so you do not need to install one.
2. Download SDRTrunk from the GitHub releases page. Grab the ZIP for your platform: Windows, Linux or macOS, each in x86_64 and aarch64 builds.
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.
5. Mac users: the SDRTrunk README warns that releases fail to launch on macOS Tahoe 26.x because of USB changes, and points to the nightly build and a libusb workaround. Check the README before installing.

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 into the powered hub (not directly into the PC).
3. Attach short SMA jumpers from each dongle 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 the tuners view: each dongle should appear. SDRTrunk shares them out between the control channel and traffic channels itself.

Step 3: Import Your System from RadioReference

SDRTrunk doesn't come preloaded with US public safety systems. Its Playlist Editor can pull them from RadioReference.com, which requires a RadioReference Premium subscription ($15 for 6 months or $30 a year as of October 2026). In SDRTrunk:

1. Open the Playlist Editor and its Radio Reference tab, and log in.
2. Filter by country, state and county, and find your system under the trunked systems list.
3. Open the system, select a site, choose which frequencies to include (for example the control channel and its alternates), and click Create Channel Configuration.
4. In the talkgroup view, Import All Talkgroups creates aliases so calls show agency names.

Without a subscription you can enter the system by hand: the control channel frequencies and the talkgroups, copied from the system's free RadioReference page. It's tedious but free.

Step 4: Configure the Channels

For a trunked P25 system you configure one channel, for the control channel, not one per voice frequency:

• Decoder: P25 Phase 1 for a Phase I control channel. Per the SDRTrunk wiki, a Phase 1 decoder on a Phase II system makes SDRTrunk create the Phase 2 traffic channels automatically.
• Frequencies: the control channel plus its alternates; the P25 decoder accepts several, so it can move if the system switches control channels.
• Max Traffic Channels: how many voice channels SDRTrunk may open at once. It defaults to three; the wiki suggests raising it toward the site's number of repeater channels if your computer can handle it.
• Preferred tuner (optional): you can pin the channel to a dongle, but SDRTrunk does not guarantee it will use that tuner.

Start the channel. When it locks onto the control channel, calls begin to appear in the Now Playing tab as SDRTrunk opens traffic channels on its own.

Step 5: Tune Gain and Verify

Each RTL-SDR has a tuner gain setting. Start in the middle of the range. If you see a lot of decode errors, try lowering gain first; if the signal is weak, raise it. Maxing gain usually adds more noise than signal near strong transmitters.

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: an encrypted call is flagged as such and won't produce audio
• Duration and signal strength

Common Problems and Fixes

Alternatives If SDRTrunk Isn't a Fit

SDRTrunk is not the only option. For comparison:

• DSD+: a Windows decoder often paired with SDR# as the front end. See our SDR software comparison.
• OP25: free, Linux-focused trunking decoder. Steeper learning curve.
• A dedicated scanner — see our RTL-SDR vs dedicated scanner comparison for when the hardware solution is simpler.

Frequently Asked Questions