Like to track balloons? How about tracking radiosondes!

Mark Conner N9XTN


Mike KD2EAT and I did a presentation a couple of years ago about tracking NWS radiosondes.  At that time, the "price of entry" was a little steep both in terms of Raspberry Pi setup and building a 1680 MHz helical antenna with an attached LNA.  

Since then, more and more of the NWS sites have migrated to 400 MHz for their sondes.  In addition, some sites use Graw and Vaisala sondes which have meteorological data that is decodeable by the Pi software.  The Lockheed Martin LMS-6 series only has lat/lon/alt data that is decodeable.  The user community reports very good 400 MHz range performance (200 mi/300 km or more if sonde is above horizon) using simple antennas (1/4 ground plane) and no preamp necessary most of the time.

If you are near a site that launches 400 MHz sondes, you can get into the tracking business with these items:
  • 403 MHz ground plane antenna (maybe $5 for a SO-239 or N bulkhead connector and some solid 12-14 ga copper wire)
  • Feedline with appropriate ends ($20-ish depending on length needed)
  • RTL-based SDR covering 400 MHz band (most of them, $20-30, Nooelec is a good brand)
  • Raspberry Pi 3B or 4 (Zero will probably not give good enough performance)
For 1680 MHz tracking, you'd need these items:
  • 1680 MHz helical antenna (3D-printer file available)
  • 1680 MHz LNA ($50)
  • Bias-T capability on the SDR to power the LNA via feedline
A note about Raspberry Pi's - they seem to be in short supply at the moment.  Pricing on Amazon is kind of high right now IMO and availability is not so great.  There appear to be plenty of 4 Gb Pi 4's available, but they're expensive and 4 Gb RAM is overkill for this application.  Pi 3's are priced well above the normal MSRP of ~$35, even allowing for typical kit parts.  More extensive searching might be worth some time.

The Linux "radiosonde_auto_rx" software is now installable within a Docker container.  You do not need in-depth knowledge of Docker to install the software, and Docker manages all the library dependencies for you.  Software updates are really simple and Mark VK5QI is very active in maintaining and upgrading this software. has all the info about how the receiver software works and how to install it.  The instructions are very clear and the user community is pretty helpful.  radiosonde_auto_rx@... is the email list. is a central location for tracking radiosondes.  You can see where current stations are receiving data (green circles) and where sondes are launched (gray).  When there are sonde flights in progress, you will also see their tracks on the site.  Clicking on a circle brings up info about the type, timing, and frequency of sondes being launched.  If the sonde site reports the sonde type is RSxx, LMS-6 403, or DFM-XX, you can receive it on a 400 MHz antenna.  This site is global in nature, with quite a few European, US, and Australian users but only a handful of Canadians appearing.  

My own station is a 1680 MHz setup that has been in operation since April 2020 - at first, just a portable setup but now a weatherproof one outside on a mast.  The local NWS office will migrate to 400 MHz next spring, so I need to get busy and build an antenna for it.  

This might make a good winter project if the weather is too unfavorable for doing ARHAB launches and chases in your area.  Sorry if this seems a little random, but I'm hoping more people in our community will give this a try. 

73 de Mark N9XTN

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