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Transmitters are typically called trackers. They are powered by a small solar panel. They are very low power and transmit on a frequency that is received around the world by radio amateurs. Typically, they send their position and altitude several times per hour. Central sites collect the information and plot it on a world map. This is explained more in the tracking section.
Make or Buy?
Make or Buy?
There are three commercially available trackers shown below. Their cost is between $40 (Zachtek) and $60 (U$B). The Traquito tracker uses an additional custom board that is soldered on to a Raspberry Pi Pico board. This is very inexpensive if you need multiple trackers. There is also the tracker that I designed which is made of three parts you can get from Amazon, but the cost is approximately the same as the Zachtek tracker. All of them transmit WSPR messages. The last option is having a custom tracker board made and then soldering on the required parts. There are links to these below.
APRS or WSPR -- APRS transmission that accounts for changes in frequency and country rules were popular several years ago. Currently nearly all trackers and balloons use only WSPR for tracking position and altitude. An APRS signal is good for a few hundred miles, while a WSPR signal will go thousands. One advantage of APRS is that it is capable of transmitting much more data than a WSPR message which makes it attractive for use with sensors that collect large amounts of data. However, if you are only interested in the thrill of going around the world, WSPR is all you need.
How do I make a tracker with three parts?
How do I make a tracker with three parts?
The goal for this project was to design a tracker so a Jr High science club could inexpensively make multiple trackers. The complete instructions are located here
This is currently my recommended tracker.
This is currently my recommended tracker.
A simpler tracker (Traquito) has been developed based upon a Raspberry Pi Pico. Instructions are located here. This tracker requires a part that needs to be ordered from China, and requires no through-hole soldering like the above. This is more like current manufacturing processes and ordering the part is simple.
Another Simple Tracker with only 2 parts
Another Simple Tracker with only 2 parts
The description of the third simple tracker option is located here. This uses only two parts, but is limited to the 20m band and requires some skilled soldering.
Ready-made trackers
Ready-made trackers
Trackquito - This is the newest addition of available trackers. It is based upon adding a daughter board to a Raspberry PI Pico. You need to have the daughter board made at JLCPCB in China which is very easy to do.
Skytracker WB8ELK
U4B – Balloon tracker (qrp-labs.com) Youtube video U4B Balloon Tracker – lightest, smallest, most powerful and flexible tracker available! – YouTube
All of these have been proven by many successful flights.
Custom Trackers
Custom Trackers
Prior to this year, the only balloons that were available for flying were “Clear Chinese Balloons.” These were thin and difficult to get to fly long distances. Weight of the tracker was critical. Consequently, several people developed light custom trackers and published their Gerber files and software on the web.
Stella – Download Project File
ICT – Download Project File
Orion Download Project File and Manual
For additional discussion search the messages and see the wiki of the picoballoon group on the groups.io site
Sending Data
Sending Data
Nearly all trackers use the WSPR network that is discussed on the tracking page. Data like altitude is encoded in the WSPR format using various coding schemes. See the tracking page for an explanation of how this network works.
Which Band Is Best for Balloons
Which Band Is Best for Balloons
Trackers are capable of transmitting on within the WSPR sub band on several bands. The most popular are 20 m and 10 m. An analysis performed for the data of February 2024 found that there is a slight advantage to using the 10 m band. The 17 m and 15 m bands are also useful, but there was not enough data available to properly evaluate these bands. Here is a link to the full analysis.
WSPR Message Format
WSPR Message Format
A single WSPR message takes 2 minutes to send. They are only sent on even numbered minutes. The standard WSPR message contains three pieces of information: the callsign of the transmitter's owner, the location and the power of the transmitter. Balloon trackers will typically send two messages of this type. The first is a standard message except instead of power, the tracker will encode a rough altitude measurement which is to the nearest 1000 m. The second message will follow the first message but instead of a the callsign will be encoded to contain information like the last three digits of the altitude (fine altitude), the temperature, and more detailed location information. The second message is encoded using a different standard depending on the type of tracker. Here are the various standards supported by the lu7aa.org.ar tracking site: wb8elk, qrplabs, lightaprs, zachtek, yo3ict, dl6ow, ab5ss, oshpark, bss99, and 6locators. The first four are commercial trackers. The wb8elk encoding is simple. It can easily be decoded (described here) without binary math. A popular alternative scheme, qrplabs encoding, is described in the picoballoon group.io wiki.
Telemetry Transmission
Telemetry Transmission
Besides the standard WSPR message, there is also a message that follows that caries additional data. This is the telemetry transmission that is transmitted following the standard WSPR message. These are in the same format as a WSPR message. However, they do not contain a callsign. Since they do not contain a callsign, how can you tell which one belongs to you? There are two techniques. Both of theses are decoded by the lu7aa.org.ar website.
One of 30 unused callsigns.
One of 5 time slots (transmissions are repeated every 10 minutes)
Encode the telemetry message using the same 4 character grid square that was used in the standard message. So fir there are two balloons that have chosen the same callsign and time slot, they can be differentiated using the grid square.
The telemetry provides 600 channels. That is to say, 600 different flights could be operating concurrently without any possibility of interfering with each other. The qrplabs website provides a way to register you flight to prevent overlap.
This technique requires the user to select one of 600 channels. A channel consists of a selection of:
One of 30 unused callsigns.
One of 5 time slots (transmissions are repeated every 10 minutes)
One of 4 frequency channels
Additional Sensor Data
Additional Sensor Data
Recently there has been interest in sending additional sensors such as high accuracy pressure transducers, gamma ray detectors or UV sensors. These can be accommodated using custom coding and a variation of the wb8elk encoding using additional unused callsigns. There are ony two trackers that are capable of this type of extension. The qrplabs tracker provides a way to extend its code using Basic programming. It currenly has some flaws that prevent this extension from working properly. My three prat tracker was designed with this in mind and has been used in conjunction with a gamma ray detector to measure radiation around the world. The tracker code is made to be a framework for extensions of this type. It can be programmed with the Arduino IDE and can utilize any sensor library that is compatible with the cpu. Currently, the tracker uses a Arduino Pro Mini, but new version is being developed to use a more modern processor and a custom circuit board option. It will have more memory and be capable of APRS transmission as well as WSPR. Completion is expected in the Fall of 23.
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