On average, the month of May sees more tornadoes than any other time of the year. One underrated technology that can help you track local weather and emergencies is the Software Defined Radio (SDR). Because of their flexibility, SDR receivers can have huge advantages over internet-based sources that might be delayed by several minutes.
Radio Licensing Disclaimer
Before attempting to operate any radio receiver, check applicable laws in your area. Some jurisdictions across the globe require a radio license to receive certain parts of the radio spectrum featured here. Others will ban the reception of these radio bands or services entirely.
Hardware Used
For this specific build, you can use the popular RTL-SDR (Realtek Software Defined Radio) chipset.
- Adjustable dipole antenna
- Dipole antenna mount
- (for Linux) Raspberry Pi 3B+
- (for Windows) Windows 10 Laptop
The RTL-SDR is a USB-compatible device that is slightly larger than a USB flash drive. These are sold by many tech companies with quite a bit of variation in quality and added features between them. Luckily, the RTL2832U demodulation chip (or a close variant) is at the heart of every RTL-SDR device, making the RTL-SDR drivers practically universal.
In addition to using a conventional desktop, laptop, or tablet; there are RTL-SDR applications for smartphones and single-board computers like the Raspberry Pi. For a quick guide on setting up a Raspberry Pi to work with an RTL-SDR receiver, visit our SDR for Raspberry Pi Setup Guide (2019).
Software Used
In Linux environments—including Debian, Ubuntu, and Raspbian—the most basic software for using an RTL-SDR receiver is simply the package: rtl-sdr. However, after you install it, you may want to also install the graphical application: GQRX.
Software Used for Raspberry Pi:
- rtl-sdr (a command line application)
- GQRX (a graphical application)
Software Used in Windows 10:
- Zadig.exe (for RTL-SDR software driver management)
- Airspy (previously called SDR# and SDR Sharp)
- VB-Audio Virtual Cable (for audio piping)
- DSDPlus (for Digital Speech Decoding)
Emergency Services
Public services like police, fire rescue, transportation services, and even snow removal are coordinated through radio broadcasts that an RTL-SDR dongle can receive with just a little software. As of 2020, there are two systems predominantly in use globally:
- Association of Public-Safety Communications Officials-International (APCO) Project 25
- Terrestrial Trunked Radio (TETRA)
Both of these are digital radio formats. APCO Project 25 (or simply “P25”) is the de facto standard in North America; while TETRA is the counterpart used within Europe, Asia, and Africa. Many cities also maintain their legacy analog systems for national interoperability; but if you’re hoping for easy reception in an urban or suburban area, you should plan on receiving P25 or TETRA.
Raw P25 and TETRA emissions are unintelligible until you decode it…
- In Windows, DSDPlus is a command-line application that will decode unfiltered audio from an application like Airspy. You will need to link the two with a virtual audio cable first. The virtual audio cable’s input and output will both appear on your computer as audio devices (just as a microphone and speaker would). You then set Airspy to output its audio to the virtual audio cable input; while you set DSDPlus to listen to the virtual audio cable output.
- In Linux, OP25 program is a popular decoding tool.
It is important to note this achieves decoding, not decryption. Decoding will not reveal the secret portions of a message, which is good because it would spell privacy issues and possibly legal trouble if it did. Large metro areas in 2020 are increasingly encrypting larger portions of their radio traffic—effectively making them inaccessible to the general public.
In North America, these services will likely be near the 852 MHz part of the radio spectrum, so plan accordingly when purchasing your antenna.
If you are listening to emergency services during severe weather, try to keep in mind that the respective agencies will be mostly concerned with their normal day to day operations. They won’t necessarily relay anything weather-related until after conditions begin to interfere with said operations. Dispatchers may relay National Weather Service (NWS) alerts, watches, and warnings; but this information will be delayed by several minutes.
To get your information sooner, consider finding a local ham radio repeater…
Ham Radio Repeaters
Repeaters are radio sites that receive and re-transmit messages from smaller radios in the area. Repeaters and the ham radios they serve operate separately from the cellular network. This makes them a useful resource for RTL-SDR operators, especially if the normal communications infrastructure is compromised by a natural disaster.
When severe thunderstorms, floods, tornadoes, or similar events unfold, the NWS will activate spotters in the area.
Spotters are volunteers who either have a strong interest in weather or work with some type of public service. When an event unfolds, the spotters may be tasked with reporting dangerous natural events like tornadoes, flooding, hail, or extreme winds. According to the NWS, about two-thirds of volunteer spotters are also licensed, amateur radio operators.
Your SDR can receive spotter radio by tuning into a Skywarn-designated ham radio repeater during a spotter activation event. What frequency will they use? Each community does things a little differently, so your best bet is to visit an online database like RadioReference.com to see which repeater nearest you is designated for Skywarn use. The 2 m ham radio band near 145 MHz and the 70 cm ham radio band near 440 MHz are usually where you will find them in the United States.
National Weather Service Broadcasts
Last but not least, we have the national weather service (NWS) itself. The NWS operates hundreds of transmitters nationwide in a network called the National Oceanic and Atmospheric Administration (NOAA) Weather Radio All Hazards (NWR).
Most communities in the U.S. have at least 1 NWR station in range. Unpopulated or mountainous regions may or may not be covered. The broadcast stations always use one of the following frequencies in megahertz (MHz).
| 162.400 | 162.425 | 162.450 | 162.475 | 162.500 | 162.525 | 162.550 |
The majority of its broadcasts are analog (no voice decoder required). However, if an emergency occurs: the NWR will push a Specific Area Message Encoding (SAME) message. Many off the shelf radios are equipped to decode and display these messages.
During bad weather, these broadcasts go hand-in-hand with the Skywarn program. Although, you are probably better off prioritizing the NWR, since it is the more comprehensive of the two.
Conclusions
As a final note, the great thing about the RTL-SDR is that you can use several of them concurrently; so don’t feel limited to using just one at a time!
References
| [1] | The Weather Channel, “Your Average Tornado Risk By Month,” TWC Product and Technology LLC, 17 May 2020. [Online]. Available: https://weather.com/science/weather-explainers/news/tornado-risk-by-month. [Accessed 22 May 2020]. |
| [2] | RadioReference.com, “National Interoperability,” [Online]. Available: https://www.radioreference.com/apps/db/?aid=7742. [Accessed 22 May 2020]. |
| [3] | U.S. National Weather Services, “What is SKYWARN®,” [Online]. Available: https://www.weather.gov/lwx/skywarn_what-is-skywarn. [Accessed 22 May 2020]. |
| [4] | U.S. NOAA, “NOAA WEATHER RADIO ALL HAZARDS,” U.S. National Weather Service, [Online]. Available: https://www.weather.gov/nwr/. [Accessed 23 May 2020]. |
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