Older articles:

1. Building a UHF Band-Stop Stub Filter

   During a recent balloon launch, I communicated with the other chase teams with my mobile rig, transmitting around 441 MHz with a transmit power of 10 watts = +40 dBm.

   For the next balloon launch, I also wanted to put a 144 MHz APRS receiver on my car, but was worried about damaging the RTL-SDR dongle I would be using for receiving. RTL-SDR dongles have a maximum input of around +10 dBm with absolutely no filtering on the input, so I could potentially permanently damage the RTL-SDR dongle when I transmitted.

   Moving and separating the antennas around on the car roof and trunk might give 20 dB of isolation, but we're still at risk of permanently damaging the receiver.

   I needed ...

   Read More →

2. Sondehub Grafana Graphs for December 2024 High-Altitude Balloon Launch

   In December 2024, the SF-HAB group flew a high-altitude balloon from the San Francisco Bay Area. The flight was a partial success, with the payload recovered the next day. Only several weeks later did I find out about this excellent Sondehub Grafana instance, hosted on AWS and directly connected to the Sondehub Amateur database.

   In this post, I want to dive a bit deeper into the Horus Binary v2 telemetry that was transmitted from a reprogrammed RS41 radiosonde on this flight. This entire post is commentary and screenshots from this grafana dashboard, screenshotted here to reduce link rot. All times are in UTC on Dec 15th 2024.

   Balloon Position Graphs

   Due to the under-inflated balloon, we knew it was going ...

   Read More →

3. December 2024 High-Altitude Balloon Launch

   On Sunday 15 December 2024 the SF-HAB group got together and flew a bursting high-altitude balloon. We had a whole crew there, including Martin W6MRR, Kazu AG6NS, Robert K6RGG, John NI6D, Walter K6ATV, Benjamin KO6CNT, and Steve K6WW. Everyone helped out with assembling the payload train, filling the balloon, or documenting the launch.

   Preflight Planning

   The days before the flight we had an atmospheric river in the Pacific Northwest, so the upper winds were very unsettled. The lower-level winds were also blowing all different directions, and it rained significantly the day before. But the weather forecast for launch day was clear and sunny, and the Sondehub predictions showed a general Southeast flight. We picked Walnut Creek as the launch location ...

   Read More →

4. 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 ...

   Read More →

5. 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 ...

   Read More →

6. 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 external antenna ...

   Read More →

7. 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 ...

   Read More →

8. 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 ...

   Read More →

9. 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 to build ...

   Read More →