Tagged: public safety

A Technical Overview of the Watch Duty Wildfire Monitoring Project Powered by RTL-SDRs

Previously in 2022 we posted about Watch Duty, a nonprofit organization aiming to improve access to live public safety information regarding wildfires in California. Several populated regions of California are extremely prone to wildfires, and it's important that residents get timely notifications about nearby wildfires so they can evacuate early and/or prepare their defensible spaces.

The system works by using RTL-SDRs to monitor public safety radio channels, and ADS-B aircraft positions of firefighting aircraft in order to gather information in real time about how wildfires are moving. Volunteers monitor this information and distribute anything of importance via a smart phone app to the public. Often the information is significantly more timely compared to official channels.

Recently Nick Russel, the VP of Operations at Watch Duty sent us a link to a technical overview blog post explaining how their 'Echo' remote monitoring devices work. The post describes how Echo devices consist of a Raspberry Pi and multiple RTL-SDR Blog dongles, with all the electronics being powered via Power over Ethernet (PoE). For the antenna a wideband Discone is used. 

Inside the Watch Duty 'Echo'
Inside the Watch Duty 'Echo'

The rest of the post explains how their voice monitoring system works, how "tone out detection" works, which are orders for engines, strike teams, and other heavy equipment, how they make use of ADS-B data and how they are able to remotely maintain and update the system.

Importantly, Watch Duty note that they rely on volunteers and donations from the community, so please consider donating via the Watch Duty app.

Watch Duty | Echo Radio Project | Fixing emergency radio dead zones

Watch Duty: California Wildfire Watch Driven by RTL-SDRs

Over on Hackaday we've seen an interesting post about the non-profit "Watch Duty" wildfire reporting smart phone app for Californians. Several populated regions of California are extremely prone to wildfires, and it's important that residents get timely notifications about nearby wildfires so they can evacuate early and/or prepare their defensible spaces.

Often by the time official notifications have gone out, it is too late. To solve this, the approach Watch Duty takes is to have volunteers monitoring public safety radio channels, and ADS-B aircraft positions in order to gather information in real time. Once critical information is established, the watch duty volunteer can push out a notification via the smart phone app. 

The volunteers make use of receiver stations that consist of multiple RTL-SDR dongles with each dongle monitoring a different EMS radio system, and one additional RTL-SDR is used for ADS-B aircraft monitoring of helicopters and fire fighting aircraft. The stations appear to uplink radio data to the volunteers via a cellular modem or Starlink.

Earlier in the year Popular Science and Wired reported on Watch Duty as well, but did not mention the use of RTL-SDRs.

A Watch Duty monitoring station with multiple RTL-SDR Blog V3 dongles.
A Watch Duty monitoring station with multiple RTL-SDR Blog V3 dongles.

GNU Radio Amateur Radio Meeting: A Look at Project 25 (P25) Digital Radio

Over on their YouTube channel GNU Radio have uploaded a recent talk by Aaron Rossetto titled "A Look at Project 25 (P25) Digital Radio". The talk explains the North American public safety P25 system in great depth, and is a good watch for anyone looking into details on how the system works in a deeply technical way. He later shows some examples of his P25 decoding and recording setup. Slides can be found here, and the video is posted below.

Agenda: In this presentation, I will introduce Project 25 digital radio, with a strong emphasis on its use in North American public safety trunked radio systems, and to describe experiments monitoring and decoding P25 traffic using GNU Radio code.

  • What is Project 25?
  • A brief introduction to trunked radio
  • Diving into the P25 protocol
    • Modulation
    • Packet framing and encapsulation
    • Packet types
  • GNU Radio and P25 decoding experiments
Amateur Radio Meetup: P25 Trunked Radio