I think the most difficult task when launching a weather balloon is the recovery, that’s why the tracking part is essential. And how can you track a device? Yes, with a GPS.
The transmitter
There are many ways to track your balloon using GPS, we chose 2 (plan A and B). Our main plan was to use an APRS tracker (for more information check out APRS site, wikipedia or our presentation). We found a bundle in Byonics that included this device (MT-1000 transceiver) with its case, a high altitude GPS and V6 dipole antenna.
We really liked the idea of using this tracker because it would allow any person to see our balloon in aprs.fi in real time, and not only the actual position but the velocity and the altitude!! However, to be able to use an APRS tracker you will need a callsign.
In the following image you can see the entire trajectory of our balloon. We also marked the launching and landing site.
Nevertheless, before all the beauty happened, we had to configure the tracker (you can find all the documentation you need on Byonics website). We used the following configuration:
Now you know our plan A. Our plan B was to use the GPS on a cell phone; we created an open source app named Sky-Quest. That app was designed to upload the cell phone’s current position into a website, and in case it didn’t had data signal, it would send its location via SMS.
For more information see Sky-Quest App
The receiver
Even though everything worked fine at the end, before the launching we weren’t sure if we were going see the APRS tracker online. That is because the nearest iGate was approximately 350 km away from the launch site and 200 km from the landing site. That’s why we decided to make our own portable receiver!
To make the receiver we needed 3 things:
1. Portable VHF Radio
We got a UV-R5 radio and put 144.390 MHz frequency.
2. Cell phone with APRSdroid app
APRSdroid app has an incredible feature called AFSK that allows an audio connection (speaker/microphone) between the radio and the smartphone. For our receiver it was extremely useful because the radio would receive the signal from the APRS tracker, and then the app would decode the sound and show the coordinated sent by the tracker’s GPS and put it into a local map.
3. A cable to connect the radio to the cell phone
The AFSK option is amazing, but we needed a way to connect them without the external noise interfering. So we made a speaker/microphone cable. Our main reference was this post from 9W2SVT blog.
Below you can see the circuit schematic:
Don’t forget that to have a successful recovery, you need a very good tracking method (or methods)! In this posts we showed you only 2 options, but there are plenty more ways to do it… It’s only a matter of getting creative!
