SDR Police Scanner: Beginner's Guide to Software Defined Radio
Software Defined Radio (SDR) offers a low-cost, flexible way to monitor police and emergency communications. For under $50, you can build a digital police scanner—but it won't defeat encryption. Here's how to get started and what to expect.
First: The Encryption Reality
Before investing time in SDR setup, understand this:
SDR Cannot Decrypt
If your local police are encrypted, SDR will not help. No consumer technology can break AES-256 encryption.
SDR Works on Unencrypted
For unencrypted digital P25 systems, SDR provides a cheap alternative to expensive scanners.
Check first: Use RadioReference to see if your local agencies are encrypted. If they are, SDR is not your solution.
What is Software Defined Radio?
Traditional radios use hardware circuits to tune and demodulate signals. Software Defined Radio does this with software instead—a simple USB dongle captures raw radio waves, and your computer processes them.
This makes SDR incredibly flexible: the same $30 dongle can receive FM radio, aircraft communications, weather satellites, and police radio. The software determines what you hear.
Hardware You'll Need
RTL-SDR Blog V4
$35–$45
The RTL-SDR V4 is the current recommended model. It's a USB device that receives radio frequencies from about 24 MHz to 1.7 GHz—covering all public safety bands. Includes dipole antenna kit.
Check Price on Amazon →Computer
Existing
Windows, Mac, or Linux. Raspberry Pi also works for dedicated setups. Minimum specs are modest—any computer from the last 10 years should work.
Requirements:
- USB 2.0 or 3.0 port
- 2GB+ RAM
- Basic audio output
Tram 1411 Discone Antenna
$40–$60
The included antenna works for testing, but a discone antenna dramatically improves reception. Wide coverage, outdoor mount recommended for serious monitoring.
Check Price on Amazon →Filters (Optional)
$20-40
If you live near strong FM broadcast or cell towers, you may need filters to block interference. Not essential to start.
Alternative SDR Option
NooElec NESDR SMArTee XTR ($30–$40) — Alternative SDR with bias-T for active antennas.
View on Amazon →Software Setup: Step by Step
Install SDR Drivers
Download and install the RTL-SDR drivers for your operating system:
- Windows: Zadig to install WinUSB driver
- Mac: Homebrew install rtl-sdr
- Linux: Usually included, or apt install rtl-sdr
Install SDR Software
Choose an SDR receiver application:
- SDR++ — Modern, cross-platform (recommended)
- SDR# — Windows classic, well-documented
- GQRX — Linux/Mac option
- CubicSDR — Cross-platform alternative
All are free. SDR++ is the current best option for most users.
Test Basic Reception
Before tackling digital police, verify your setup works:
- Tune to a local FM station (88-108 MHz)
- Try NOAA weather radio (162.4-162.55 MHz)
- Listen to aircraft (118-137 MHz)
If you can hear these, your hardware and basic software are working.
Install Digital Decoder (For P25)
Most modern police use P25 digital. You need additional software to decode it:
- DSD+ (Digital Speech Decoder) — Windows, easiest option
- OP25 — Linux, powerful but complex
- SDRTrunk — Cross-platform, handles trunking
DSD+ with a virtual audio cable is the easiest path for beginners.
Configure for Your Local System
Find your local frequencies on RadioReference:
- Note the system type (conventional, P25 Phase I/II, trunked)
- Get the control channel frequency for trunked systems
- Verify encryption status—if encrypted, stop here
SDR vs. Dedicated Scanner
Which Should You Choose?
- Choose SDR if: You're tech-savvy, want to learn radio, and have budget constraints
- Choose a scanner if: You want portable, reliable, easy-to-use monitoring
- Choose neither if: Your area is encrypted—no solution will work
Prefer a dedicated scanner? The Uniden SDS100 ($550–$700) is the best portable option—no computer required.
Common SDR Challenges
Interference
Strong nearby signals (FM radio, cell towers) can overwhelm the receiver. Solutions: better antenna placement, FM bandstop filters, or gain adjustment.
Computer Noise
Computers generate electrical noise that SDR can pick up. Use a USB extension cable to move the dongle away from the computer.
Trunking Complexity
Most police systems are trunked, requiring more complex software setup. SDRTrunk or OP25 are designed for this but have learning curves.
Audio Routing
Getting audio from SDR software to decoder software requires virtual audio cables. VB-Audio Cable (free) is the common solution.
Why SDR Users Care About Encryption
Many SDR enthusiasts invest significant time learning radio technology. That investment becomes worthless when police encrypt. This is why the SDR community often becomes engaged in encryption policy debates.
If you're investing time in SDR, consider also investing in advocacy:
- Attend city council meetings when encryption is discussed
- Support hybrid systems that keep routine channels open
- Join ham radio clubs and ARRL—they often oppose encryption
- Educate others about what's lost when police go dark
Resources for Learning SDR
RTL-SDR Blog
Best tutorials and guides for getting started
RadioReference Wiki
Database of all public safety frequencies
r/RTLSDR
Reddit community for troubleshooting help
SDR++ Discord
Active community for software help
Frequently Asked Questions
Can an SDR decode encrypted police radio?
No. Software Defined Radio cannot decode encrypted police communications. SDR is a flexible receiver, but encryption is a mathematical problem that cannot be solved by any consumer technology. If your local police are encrypted, SDR will not help.
What is the cheapest way to listen to police with SDR?
An RTL-SDR V4 dongle ($30-40) plus free software (SDR++, GQRX) is the cheapest digital scanner option. Total cost under $50. However, you'll need a computer and patience for software configuration.
Is SDR better than a regular police scanner?
SDR is more flexible and cheaper, but requires technical knowledge. A dedicated scanner like the Uniden SDS100 is easier to use and more portable. SDR is best for tech enthusiasts; regular scanners are better for casual users.
What software do I need for SDR police scanning?
You'll need two types of software: 1) SDR receiver software (SDR++, SDR#, GQRX), and 2) Digital decoder software (DSD+, OP25) for P25 digital signals. All are available free.
Can I use SDR on my phone?
Yes, with Android phones using an OTG adapter and apps like SDR Touch. However, phone-based SDR is limited and not recommended for serious monitoring. A computer provides much better performance.
Take Action for Transparency
Your voice matters. Here are concrete ways to advocate for open police communications in your community.
Contact Your Representatives
Use our templates to email your local officials about police radio encryption policies.
Get StartedRead Case Studies
See how encryption has affected real communities - from Highland Park to Chicago.
View CasesSpread Awareness
Share evidence about police radio encryption with your network and community.
Public Testimony
Learn how to speak effectively at city council and public safety meetings.
Prepare to Speak