Balloon TX

Using an amateur radio protocol called Automatic Packet Reporting System (APRS) to beacon location for a high-altitude balloon launch.

The balloon will have cameras and video cams which will take cool shots of the Earth’s atmosphere.

Disclaimer

This project has been a super-long term one…. it’s been weaving in and out between classes and other life obligations.

TODO

I want to build up my own APRS-capable software and not use Tracksoar. I only wanted to use Tracksoar to see that my lower-level bit encoding was legit. This is in the works!

Current State

I forked an open-source project called Tracksoar which creates APRS trackers. I use a different microcontroller, radio transmitter, and GPS than what they do. This is just for fun for me.

Item	What Tracksoar Uses	What I Use
Microcontroller	ATMEGA32u4	Arduino Due (uses Atmel SAM3X8E)
GPS	uBlox MAX8	Adafruit GPS
Radio Transmitter	Radiometrix HX1	Si5351B

The APRS protocol in North America transmits at 144.39 MHz with Audio Frequency-Shift Keying (AFSK) with 1200 Hz and 2200 Hz tones for mark and space respectively. This means on a 144.39 MHz carrier, a 1200 Hz tone is a “high” / mark and a 2200 Hz tone is a “low” / space. This binary encoding puts the data on the carrier.

So far, a 1200 and 2200 Hz tone can be generated using direct digital synthesis (DDS) from a sine table with 512 entries.

These tones could be heard on the carrier when I tune my Baofeng radio in.

And using a Kenwood radio that has a built-in TNC decoder + using Tracksoar to verify the lowest level of bit encoding was correct, I could decode APRS messages.