It's been two months since my first radiosonde recovery. In this post, I perform some analysis of the receiving stations at my apartment in San Francisco and my vacation home/parents place in Los Gatos. I also include the python code needed to generate your own plots.

San Francisco Station

Immediately after I got home from my first recovery, I converted my regular amateur radio station at my apartment to receive radiosondes. The external antenna is a Diamond X-50NA, which is a great amateur radio 5/8 wave 2m/70cm dual-band antenna. Coax up to the roof is about 80 ft of LMR-400, which is calculated at around 1.5 dB loss at 145 MHz and 2.5 dB at 450 MHz, plus connectors. Because this had a base station radio attached, it didn't have an LNA or filter up at the antenna.

Here is a pic of the antenna, mounted to a 5 ft pole that is clamped to a steel sewage roof vent. This is a very easy (temporary) installation. The Nanostation M5 also installed is part of ...

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I've been watching SondeHub for the past two months to, every day since my first recovery, but the winds have not been cooperating! Lots of radiosondes went into the hills east of San Jose, out into the ocean, into the Santa Cruz mountains, all the way down to Gilroy, or splashed down in the bay, but none have landed in populated areas within an hours drive of my home in San Francisco. I realized how lucky I was that the first radiosonde I successfully tracked actually landed in a populated place.

In a typical city, approximately 35-50% of the land is dedicated to cars: residential roads, arterials, freeways, and parking lots. So when a balloon lands in populated areas of the Bay Area, there's a really good chance that it's going to land on or near some car infrastructure. Even my neighborhood in San Francisco, one of the densest cities in America, dedicates 28% of surface area to cars: from the center stripe to the front of the house is 40 ft, and the lot is 100 ft deep. Cars ...

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In September 2018 I built a remote receiving station for the SatNOGs project. This post describes the build process, and modifications I made to allow for coax power of a Mini-circuits ZX60-33LN-S+ low-noise amplifier.

SatNOGs is a distributed ground station network for amateur radio and university satellites. The idea is to spread a bunch of software-defined receivers around the world to help satellite operators downlink more data from their satellites. The open-source project, running on your local hardware, controls a software-defined receiver, moves directional antennas if you have them, and uploads the audio files and decoded data to a big database. Satellite operators, and other curious people, can see almost-real-time telemetry from the satellites.

As a historical aside, the concept of CubeSat teams sharing ground station resources has a long history, starting back with the first CubeSats launched in June 2003. Here's a partial list of CubeSat-specific networks that laid the foundation for the SatNOGs network:

• Professor James Cutler, from Stanford and now University of Michigan, built the Mercury Ground Station Network for commanding the Stanford QuakeSat CubeSat. Presentation.
• Japanese ...

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After my very successful SOTA activation of San Pedro Mountain the previous weekend, and the San Francisco Radio Club Angel Island expedition at the same time, the club decided to do another SOTA activation on Saturday November 14th. Antonis AA6PP, Jeff KK6JJZ, Rick K6TOR, David KN6HFV, and myself went up to the top of Mt. Davidson and activated the peak under the club's callsign W6PW.

It was a beautiful day, very clear after the rains the previous evening. We had a total of five stations. Antonis AA6PP and Jeff KK6JJZ ran the HF voice stations, trading off on 40, 20, and 15 meters during our activation. Rick K6TOR ran HF CW, and Dave KN6HFV ran the UHF station on 445.525 MHz with his HT and an Elk Antennas 5-element log periodic antenna.

Here is Antonis AA6PP running one of the HF SSB stations with an Elecraft KX2 transciever, AX1 multi-band whip antenna, powered from a Bioenno 4.5 Ah LiFePO4 battery. Notice the antenna counterpoise on the ground, stretched out in front of him.

I was using the same ...

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Summits on the Air (SOTA) combines two of my favorite pastimes, amateur radio and hiking. The objective is to climb to a nearby peak, then contact as many people as you can on the radio. While most SOTA peak activations are on HF, my only portable gear at the moment is a few HTs.

On Saturday Nov 7th, I activated San Pedro Mountain, which is 1058 ft tall. It's located in Harry A. Barbier Memorial Park in the hills above San Rafael, next to China Camp State Park.

I took the Knight Dr route, from Tom AI6CU, hiking along the Ridge Fire Road. The hike up took about 45 minutes, and some sections of the trail were very steep. I arrived on top about 12:30pm, ate a quick sandwich, and cooled off.

The radio equipment I was using was a 3-element Arrow II yagi antenna, and my trusty Icom IC-T7H handheld transceiver. RF output was about 1 watt, and the gain of the antenna was about 5 dB. Unfortunately, I only had a metal broomstick to hold the yagi ...

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I've recently stumbled upon the radiosonde_auto_rx project. I've always been interested in tracking radiosondes, and even watched a radiosonde launch in Inuvik, NWT a few years back. Worldwide, there are over 800 launches every twelve hours of every day, and this data feeds into weather forecast models.

The radiosonde_auto_rx project is built around decoding many different types of radiosondes with a software-defined receiver. The preferred receiver is a RTL-SDR Blog v3, and I already had an extra one of those (because they are so inexpensive!).

Most radiosondes worldwide use 400-406 MHz as their downlink, but the United States also uses some frequencies around 1680 MHz. Reading the documentation on which frequencies are in use, it appeared that 1680 MHz was being used at Oakland, but they were transitioning over to 400 MHz "sometime in 2020." So first step was to install the software, then find what frequency band the radiosondes were on.

Software Install

The radiosonde_auto_rx program is designed for Raspbian/Debian systems. I use a crappy laptop with Ubuntu for my APRS balloon tracking, so I decided to use ...

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Automatic Identification System is a system for boats to broadcast their location. This is very helpful in congested waters, such as in the San Francisco Bay, where many ferries, huge container ships, and small pleasure craft are trying to avoid each other. Onboard digital chart plotters can show nearby ships, their heading, speed, and expected position a few minutes from now. Early AIS transmitters were very expensive, but the new generation of Class B transmitters are actually pretty inexpensive.

AIS operates on two frequencies, Marine VHF channels 87B and 88B. These are the high-side duplex frequencies of channel 87 and 88, and they are 161.975 and 162.025 MHz. The data link layer is 9600 baud GMSK, packet length of 256 bytes, which works out to 26.6 millisecond packet time including some guard time. Each AIS "frame" is 1 minute long, so within each frame there can be 2250 time slots (per frequency). With two channels available, a lot of positions can be transmitted every minute.

The boats use a self-organizing time division multiple access (SOTDMA) scheme, which ...

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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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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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In September 2016 I visited the Environment Canada Weather Station in Inuvik, NWT. I arrived just as they were preparing for the 2300z weather balloon launch, and they let me hang around and take some pictures.

Every twelve hours around the globe, approximatley 800 radiosondes are launched. These weather balloons record temperature, pressure, humidity, and location from the surface all the way up to 100k feet, or higher. These measurement are fed into weather models for long-term weather forecasting. These launches happen worldwide at 1100 and 2300 UTC, which gives the balloon enough time to be up at altitude around noon and midnight UTC.

This is the Vaisala RS92-SGPD radiosonde, which measures location, pressure, temperature, and humidity as the balloon ascends. The helix antenna in the upper right is for GPS, and the silver strip below that has two temp sensors and a humidity sensor. The 402.7 MHz wire antenna is on the bottom of the unit, on the left side. The 200 ft of string on the spool attaches to the balloon.

The balloon is filled with locally-generated ...

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