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Reimagining the police scanner in the era of the SDR

Taking scanning to the next level using distributed RTLSDR receivers & open source software

Presented by Gavin Rozzi

Cyberspectrum #23 @ DEF CON 2018

August 9th, 2018

SDR has the potential

to expand public knowledge while reducing cost & complexity

The problem with hardware scanners

Hardware scanners are expensive

Digital scanners especially those capable of newer digital protocols are pricey.

P25 Phase II scanner - $400

RTLSDR dongle - $25

Hardware scanners have limitations

Traditional scanners can only receive one transmission at a time. But large trunked systems could have activity on multiple channels at once, forcing users to miss out.

For many, new digital scanners are out of reach

As agencies continue to adopt radios that use digital modulation. Many scanner enthusiasts are unable or unwilling to obtaing digital scanners due to cost and complexity.

Live feeds aren’t much better

They compensate for some shortcomings and allow portability, but are still limited by the constraints of hardware scanners.

Enter OC Radio Live

Using SDR & open source technologies, we can make scanning easier and more user-friendly. OC Radio Live is a website that I created to use SDR to stream transmissions from local radio systems.

Screenshot

How scanning can be better with SDR

OC Radio Live features:

  • Time shifting, so simultaneous scanner calls on different channels are saved.
  • Multiple receiving sites can allow wide area coverage
  • Transmissions are stored and archived by talkgroup & scanlist
  • Unlike traditional scanner feed archives, no silence is recorded, only activity on channels.

How scanning can be better with SDR

Thanks to trunk-recorder we can record:

  • Conventional analog repeater / simplex channels
  • Motorola analog trunked systems
  • P25 Phase 1 & 2 digital trunking systems

Ocean County, NJ’s Radio Systems

These capabilities allow us to record the following types of systems using the site:

Aging 500 MHz Motorola Type II TRS

New State & County 700 MHz P25 Phase II systems

Analog VHF and UHF conventional channels

More Choices

Hardware scanners only offer a simple lockout and various banks of channels. OC Radio Live has data on invididual channels, entire radio systems and custom scan lists for regions and types of radio traffic.

Scan lists on the site

Our Receiving Sites

Toms River, NJ (700, 460 and 155 MHz) (outside) Toms River 700 receiving site

Our Receiving Sites

Lacey, NJ (500 MHz) (inside) Lacey Township receiving site

The open-source software powering the site

The backend

  • trunk-recorder by Luke Berndt
  • Radio transmissions are saved to an Amazon S3 bucket
  • Desktop with powered USB hubs at receiving site 1
  • 2U server along with an Ubuntu desktop with 4 SDRs at receiving site 2

The backend

trunk-recorder uses JSON syntax for defining systems and SDRs. Some examples of the systems I defined are on Github A screenshot of a config file

The backend

Scanning the NJICS 700 MHz system trunk-recorder uploading transmissions

The frontend

The frontend is hosted on a simple Ubuntu 16.04 VPS on a cloud hosting provider.

  • Django web framework
  • Nginx as a reverse proxy to daphne
  • trunk-player handles the scanning interface

Bringing it all together

  • trunk-recorder reads in the JSON configuration file for the system(s) and allocates recorders on multiple RF channels within the SDR’s bandwidth.
  • A bash script passes the transmissions along with JSON metadata to the frontend server, where it is written to a database.
  • The transmissions are uploaded to Amazon S3 for storage and deleted from the frontend.
  • Users can play live transmissions & access archives on the frontend website.

A REST API Endpoint for every radio system

Example request:

curl https://ocradio.live/api_v1/scan/default/?format=json

A sample API response

Conclusion

SDR can break down cost & complexity barriers to monitoring public safety radio systems. SDR combined with web services can allow receiving setups previously not possible with past hardware radios.

Site demonstration + Q & A