Best SDR for P25 Trunking: Phase I and Phase II in 2026
Following a modern P25 trunked radio system with SDR is a different problem from casual monitoring. You need enough bandwidth to see the control channel plus voice, reliable frequency stability, and software that can decode Phase II. Here's what actually works.
What Makes a Good P25 Trunking SDR
P25 trunked systems work by announcing on a control channel which frequency will carry the next voice transmission. Your SDR has to either follow that announcement and retune fast enough (harder than it sounds on Phase II) or cover enough bandwidth to sit on control and voice simultaneously.
The checklist:
- Frequency range — must cover the band your agency uses (150 MHz, 450 MHz, or 700/800 MHz)
- Frequency stability — a TCXO (1 PPM or better) is strongly preferred. Drifting dongles lose control channel lock.
- Bandwidth — either 2.4 MHz × 2 dongles, or a single dongle with 6+ MHz
- Software support — must work with SDRTrunk or DSD+ Fastlane
- Linux/Windows driver maturity — newer tuners sometimes lag on driver support
Ranked SDR Picks for P25 Trunking
RTL-SDR Blog V4 × 2
$35-45 each — total ~$70
Two V4s running SDRTrunk is the reference budget setup. One dongle dedicates to the control channel; the other tunes to voice channels as they're announced. The 1 PPM TCXO on each V4 keeps control channel lock steady, and the improved filtering handles broadcast overload that would kill older dongles.
Works for: P25 Phase I, P25 Phase II, DMR, NXDN via SDRTrunk.
Check Price on Amazon →Airspy Mini
$99–$129
The Airspy Mini is a single-dongle answer. Its 6 MHz of usable bandwidth typically covers both the control channel and all voice channels of a P25 Phase II site simultaneously, so one Mini replaces two RTL-SDRs. The 12-bit ADC handles strong-signal environments better than RTL-SDR, and SDRTrunk supports it natively.
Works for: P25 Phase I, P25 Phase II on most systems, DMR, NXDN.
Check Price on Amazon →SDRplay RSP1A or RSPdx
$109–$249 depending on model
SDRplay receivers provide up to 10 MHz of bandwidth, which is more than enough for any P25 Phase II system. The 14-bit ADC delivers clean decoding. The trade-off is software setup — SDRTrunk requires the SDRplay API and sometimes the RSPtcp bridge depending on your OS. See our SDRplay vs RTL-SDR comparison for the full picture.
Works for: All P25, DMR, NXDN, plus HF and wideband spectrum work.
Airspy HF+ Discovery
$169–$219
Despite being an excellent receiver, the HF+ Discovery caps at 260 MHz. It won't tune 450 MHz, 700 MHz, or 800 MHz where nearly all US P25 systems live. If you're shopping Airspy specifically for P25, buy the Mini, not the HF+.
Generic "RTL2832U" dongles on Amazon
$15–$25
Cheap RTL-SDR clones without a TCXO drift too much to hold a P25 control channel. Save yourself the frustration and buy a genuine RTL-SDR Blog V4.
Hardware Beyond the Dongle
Every P25 trunking build also needs:
- A powered USB hub — 5V/3A minimum, with independent port power preferred. Two or three dongles on an unpowered port sag voltage and drop calls.
- A wideband outdoor antenna — a discone like the Tram 1411 handles 150–1300 MHz with one element. Stock telescoping antennas will miss weak sites.
- Good coax — RG-58 is fine for short runs (under 25 ft). LMR-240 or LMR-400 if you need more distance. Our SDR antennas guide covers the full picture.
- A PC with Java 21 — SDRTrunk's current requirement. 8 GB RAM, modern quad-core CPU, SSD for logs.
How to Tell If Your System Is Encrypted
Before buying hardware, confirm your target system is worth monitoring. Check RadioReference.com for your county or state. Look for these flags:
- "ENC" or "E" on talkgroups — encrypted traffic
- "DE" — partial encryption (some talkgroups encrypted, others not)
- No flag — unencrypted, monitorable with SDRTrunk
If every primary law enforcement talkgroup shows "ENC," an SDR build won't get you audio. It may still be worth building one for fire/EMS or for adjacent agencies. See our encrypted agencies database for the current state of each state's systems.
Best Overall / Best Value / Best Budget
Best Overall
2 × RTL-SDR V4 + SDRTrunk
~$70 total
The most capable P25 trunking setup under $100. See the setup guide.
Best Single-Dongle
Airspy Mini
$99–$129
If you want one dongle instead of two, this is the pick.
Best Starter
1 × RTL-SDR V4
$35-45
Good enough for P25 Phase I conventional systems. Upgrade to two dongles when you need Phase II.
Frequently Asked Questions
Can an RTL-SDR decode P25 Phase II?
Yes, but the reliable way is two RTL-SDR V4s running SDRTrunk — one on the control channel, one on voice. A single 2.4 MHz RTL-SDR will miss calls on busy Phase II systems because the control and voice channels often sit more than 2.4 MHz apart in the band allocation.
Is Airspy HF+ Discovery good for P25?
No. The HF+ Discovery doesn't cover the 450 MHz or 700/800 MHz bands where nearly all P25 trunked systems operate. It tops out at 260 MHz. If you want an Airspy for P25, get the Airspy Mini instead.
What's the cheapest SDR setup for P25 trunking?
Two RTL-SDR Blog V4 dongles, a powered USB hub, a wideband antenna (discone), and SDRTrunk software. Total hardware cost around $120–$140, plus a PC you already own. Our SDRTrunk setup guide walks through the full build.
Do I need special software for P25 Phase II?
SDRTrunk handles Phase II natively and is free. DSD+ Fastlane (paid) also handles Phase II with very good audio quality. The free version of DSD+ supports basic Phase II but Fastlane is noticeably better on busy systems.
Will SDR work if my department encrypts?
No. Once a P25 system uses AES-256 (or even older DES-OFB or ADP encryption), no consumer SDR or scanner can decode the audio. SDRTrunk will still log that encrypted calls happened and identify talkgroups, but you'll hear silence instead of voice.
How much bandwidth do I need for P25 trunking?
For P25 Phase I, a 2.4 MHz receiver (RTL-SDR) usually fits the active channels. For Phase II, you either need two 2.4 MHz receivers following control and voice separately, or a single wider receiver (Airspy Mini at 6 MHz, SDRplay at 10 MHz) that can cover the whole allocation.
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