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1. Reprogramming a RS41 Radiosonde for Amateur Radio Frequencies

   I decided to re-fly a Vaisala RS41 radiosonde on an upcoming SF-HAB high-altitude balloon launch. The radiosonde must be reprogrammed on amateur radio frequencies, and I decided to use the RS41ng project by Mikael Nousiainen OH3BHX. This post is a companion post to setting up a Horus Binary receiving station.

   Radiosonde Hardware

   The radiosonde I randomly pulled out of my box was V1920305, launched over a year ago from Oakland on 8 August 2023. I picked it up the next morning from a construction zone in South San Francisco, and the construction guys just gave it to me after I asked about a balloon.

   

   Building the firmware

   On Linux, building the RS41ng firmware is ridiculously easy. You build a local ...

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2. Setting Up a Linux Horus Binary Receiving Station

   The SF-HAB group is talking about doing a High-Altitude Balloon launch in the next few weeks, and asked if I had any payloads to fly. I thought it would be fun to refly all these radiosondes that I have collected.

   Looking around a projects online for reprogramming radiosondes, I came across the the great work that Mark Jessop VK5QI was doing down in Australia. Mark and David Rowe created the Horus Binary protocol, which is a low-power 100 baud 4FSK modulation scheme specifically designed for high-altitude balloons. Mikael Nousiainen OH3BHX wrote the RS41ng project which implements the Horus Binary transmitter on a regular Vaisala RS41 radiosonde.

   The next blog post will focus on reprogramming the RS41 radiosonde.

   Hardware Setup

   The ...

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3. Keflavik, Iceland Radiosonde Receiver

   I spent a few weeks in Iceland in May 2024, working near the main airport in Keflavik. The area was a US Air Force/NATO base from 1951 until 2006, when it was turned over to the Icelandic government. The US Air Force returned in 2016.

   While I was there, I installed a radiosonde_auto_rx station. Iceland has one radiosonde launching site located at the Keflavik airport, and launches two radiosondes a day at 1100 and 2300 UTC. Skew-T plots are published by the Iceland Met Office after every launch.

   Hardware

   The hardware for this receiving site is the standard radiosonde receiving hardware. A Rasbperry Pi 3B+ and a RTL-SDR Blog v3 are the main components, along with an ...

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4. Digital Communications Inc DCI-146-4H Band-Pass Filter

   I recently acquired a Digital Communications Inc. DCI-146-4H band-pass filter. This is a 4-pole cavity filter for the 2 meter Amateur radio band, with a pass band of 144 to 148 MHz. Physically it's about 12" long, 6" high, and 3" deep, and is very light. The connectors are UHF SO-239.

   

   I purchased this band-pass filter for operating Summits On The Air (SOTA) radio events. Operating 2 meters FM simplex on the top of mountains is a lot of fun, but many SOTA mountains also have high-powered broadcast transmitters, public safety repeater systems, etc. These strong transmitters cause desensitization in receivers, and I can't hear other stations unless they are very strong. This type of band-pass filter removes all out-of-band ...

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5. Japan Radiosonde Recovery and Tracking

   In July 2023 another work trip took me to Hokkaido, Japan. I stayed in Obihiro, a city of about 165,000 people. I brought along a RTL-SDR dongle and mag-mount antenna, and if I had some free time, I would try and decode nearby radiosondes.

   From my earlier trip back in September 2022, I knew there was radiosondes launched from Sapporo twice a day. However, it was unclear if the Kushiro autolauncher had been replaced after the fire.

   

   After tracking the radiosondes in Hokkaido, I would travel to Tokyo for a few days and try and track them in the city, labeled "Tateno" in the above map.

   Tracking Hardware

   The equipment I use is very simple but effective, just a ...

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6. Fairbanks Radiosonde Receiving Station

   After my visit to Fairbanks, Alaska back in July 2022, I chatted with a friend who lives in Fairbanks. He agreed to host a radiosonde receiver at his house just north of town. Since I wasn't traveling to Fairbanks again in 2022, I shipped him all the parts necessary for the installation.

   

   This station is the standard Raspberry Pi and RTL-SDR Blog v3 that I have been shipping around to Houston and other sites. radiosonde_auto_rx runs inside a docker container, which makes it trivial to install and update the software. For remote monitoring and control, wireguard is the way to go.

   Antenna

   My go-to antenna for radiosonde receiving is a quarter-wave ground plane antenna. They are super easy ...

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7. Kushiro, Japan, Radiosonde Autolauncher

   A recent work trip brought me to Hokkaido, Japan. Taking a look at Sondehub beforehand, I noticed a few radiosonde launch sites on the island. My work would bring me closest to the Kushiro radiosonde launch site, so maybe if I had some free time I could go watch a launch.

   Research

   Before leaving for the trip, I contacted Shaun JH1HNB/KJ6VGQ, who was uploading radiosonde data to Sondehub. Shaun lives in Tokyo, and has written some blog posts about his experiences.

   Shaun gave a presentation (pdf) in February 2022 to the Tokyo International Amateur Radio Association. The presentation was about using radiosonde_auto_rx or a rdzTTGOsonde to receive radiosondes.

   

   I also did some research on the Japan Meteorological ...

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8. Adding a Bodnar GPS Disciplined Oscillator to a KiwiSDR

   With the release of WSJT-X 2.3.0 in September 2020, Steve Franke K9AN, Bill Somerville G4WJS, and Joe Taylor K1JT included a two new digital protocols called FST4 and FST4W. These two digital modes are the next evolution in low-power and long distance digital communications. These modes use four-level Gaussian frequency-shift keying (4-GFSK) modulation, which has smooth transitions between the four tones. This modulation is a bit easier to decode than regular WSPR, which uses 4-FSK modulation that has abrupt tone changes.

   FST4 is designed for keyboard-to-keyboard QSOs (similar to FT8), and FST4W is designed for beacon transmissions like the regular WSPR protocol that we use for picoballoons. The time periods for a single transmission are 120, 300, 900 ...

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9. Installing a WSPR Receiver in Inuvik, NWT

   I recently set up a Weak Signal Propogation Reporter receiver in the town of Inuvik, NWT. I was there in the beginning of June 2022, just as the world was opening back up from the COVID-19 travel restrictions.

   

   I thought Inuvik would be an interesting place, as it's at 68 degrees North latitude, which is above the Arctic Circle. During the summer, the sun never sets from May 25th to July 19th. In the winter, the sun doesn't rise from Dec 6th to Jan 5th. But the sun does get close enough to the horizon to have civil twilight, where the sun is less than 6 degrees below the horizon, so it's not completely dark all the time in the ...

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