The tracking equipment for a high altitude balloon using the amateur radio frequencies is fairly straightforward. Most of the equipment can be purchased off the shelf and used equipment is easy to find. My high altitude balloon uses the Automatic Packet Reporting System (APRS) on the national APRS frequency of 144.39 MHz to report its current position and altitude. The main components needed to receive the position data are a ham radio, terminal node controller (TNC), and a laptop.
I chose the Alinco DJ-175T handheld radio to receive the 144.39 MHz signal. It’s relatively inexpensive and Alinco is a reputable company. Handheld radios are not suitable for use inside a car, which is where most of the chasing will occur. They have a ‘rubber ducky’ antenna (normal-mode helix antenna) which has poor performance compared to a larger antenna. Using this type of antenna inside of a car reduces the performance even further. Therefore, I purchased a mag-mount antenna and an adapter to mate the antenna to the handheld radio. This will allow me to have the antenna mounted outside my vehicle while the radio is inside.
The speaker port on the handheld radio allows the received signal to be sent out to an external device. A terminal node controller demodulates the incoming audio signal, interprets the data, and sends the output over a port in a usable form. The TNC performs all of the functions necessary to participate in an AX.25 network, which is what the APRS system utilizes. I chose the Kantronics KPC-3 (non-plus) with the 8.2 firmware (enables APRS capability). This was a very popular TNC and they are still in use today, but you can only find used ones now.
I created a cable using the information in the DJ-175T and KPC-3 manuals to connect the two units. A 3.5mm mono audio jack plugs into the speaker port of the handheld radio and a 9-pin DSub connector plugs into the TNC. Only two wires are needed for receive-only. Then I purchased a 25-pin DSub connector to 9-pin DSub connector adapter and connected it to a serial-USB adapter cable I already owned. This completes the connection to the laptop.
The laptop is running Balloon Track software available from Edge of Space Sciences. This software will track a balloon, predict the flight path in real-time using live data, and even plot the current position and predicted landing site on a map.
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