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1. Mobile Horus Binary v2 and APRS Receiving Station with Raspberry Pi

   After the previous December HAB launch, I realized that I needed to spend some time on my receive hardware setup in the car. I previously had a VirtualBox VM running Horus-GUI and headless horusdemodlib, but it was very much a kludge. As an upgrade, I wanted to add APRS reception for the balloon 2 meter APRS tracker.

   In order to keep track of all the hardware required for this, I created a block diagram using draw.io desktop. Click to make bigger.

   

   The next sections will describe the different parts of this setup.

   RF Filtering

   I quickly realized that having two RTL-SDR dongles in close proximity to a 10 or 50 watt transmitter might cause problems. It would certainly desense the receivers during transmission, but it also might cause permanent damage to the dongles. Permanent damage is hard to diagnose because there's no error message saying "broken," it just doesn't receive weak signals (or any signals at all).

   Filtering the 441 MHz voice transmission out of the 144.39 MHz APRS receiver is pretty easy, as those frequencies are very ...

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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 to rise slower than predicted, and burst at a higher altitude. This balloon reached a maximum of 37,412 meters (~122.7k feet) at 21:09:57.

   

   This is a graph of the ascent and descent rates for the whole flight. The blue line is what the GPS reports (in meters/sec, left axis), and the yellow line is calculated ...

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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 to have our balloon land on the eastern side of the Central Valley

   

   Balloon Assembly and Filling

   The launch site was at a local park in Walnut Creek, and we met at 9:30am on a very cool and cloudy day. There was no wind at all. The balloon was a standard Kaymont 1500 gram filled with hydrogen.

   

   Unfortunately, during ...

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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 docker container with the build environment, which takes up about 2.2 GBytes of storage (!?). After editing the configuration file, one command builds the firmware inside the docker container.

   Here are the commands I ran, stolen from the detailed linux docker procedures:

   ~$ git clone https://github.com/mikaelnousiainen/RS41ng
   ~$ cd RS41ng
   ~/RS41ng$ vim src/config.h                                                        (edit with your configuration ...

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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 hardware receiving the Horus is pretty much the same as receiving a radiosonde or AIS, except it's a different frequency so a different antenna must be used. While I list a Raspberry Pi 4 on the block diagram (running Debian 12 Bookworm), any Debian-based distribution can be used.

   

   The Mt. Carmel High School Amateur Radio Club (W6SUN) down in San ...

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6. High-Altitude Balloon Launch from Davis

   The SF-HAB group got together in the beginning of August to do another high-altitude balloon launch. The purpose was to test out a new 3D GoPro camera to see how well it would perform at altitude. We also had a LoRA transciever onboard, which we are thinking about using as a remote cutdown device that we would fly on future launches.

   The jet stream in July was really unsettled, so we delayed for a few weeks while the winds picked up a bit and shifted heading. Watching the predictions from HABHUB gave us a good idea when to launch. This was one of our predictions before launch.

   

   Unfortunately, I really goofed up when doing the launch predictions. As you can see in the above screenshot, I used the default ascent rate of 3.5 m/s, which is about 680 ft/min. We normally target 1000 ft/min, so this prediction has the balloon going much further than what we were looking for.

   I realized my mistake and ran some more predictions, plus the winds changed slightly overnight, so we ...

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7. High-Altitude Balloon Launch from the Berkeley Marina

   After the success of the KD4STH launch in September, we decided to do it again! A new group formed for San Francisco High Altitude Balloons (SF-HAB), and we started scheming. The hardware and time stars finally aligned on Sunday March 8th, and we decided to launch from the Berkeley Marina. Unbeknownst to us, this was only a few days before the whole world shut down due to COVID-19. Great timing!

   

   

   The balloon was a Kaymont 3kg balloon, and we used an entire K-sized tank of hydrogen for lift. Unlike some previous launches, we didn't use weights to carefully measure/specify the ascent rate, we just used the whole tank. During the chase, we calculated our ascent rate at about 1400 ft/min, which was faster than our target of 1000 ft/min. Faster ascent means the balloon is not being pushed around by the wind as much, but it will burst at a lower altitude if the balloon is overfilled. Since this was a 3kg balloon, it was not overfilled.

   

   The primary mission of this launch was to fly a ...

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