Aerocomm AC4490LR-1000M

                The communications system our balloon utilizes are the Laird Technologies Aerocomm AC4490LR-1000M radios. The radios operate on 900MHz frequencies and have a max operating range of 40 miles with a clear line of sight. The radios also require a low amount of power to operate at their full potential. The radios are small and lightweight. These traits make them ideal for our high altitude weather balloon. Since the radios use amateur bands of radio frequencies to operate, two of our group members have obtained our amateur radio licenses so that we may legally use the radios for our project.

                The group is using a AC4490 developer's kit to make the configuration of the radios easier. The software that comes with the dev kit is designed for easy configuration of the radios and allows the users to set them up in any way you'd need. Our set up is fairly simple. A radio (the client) will be wired to the PCB in our payload and an antenna connected to the radio will poke its way through the payload wall which should provide an easy line of site to the ground station. The ground station will consist of our other radio (the server) connected to a laptop which will be receiving signals from the balloon. The picture below shows the server radio wired to a board which connects to our ground station laptop via USB cable.

                The software which Laird has provided as a configuration utility can be rather clunky at times. The program is susceptible to random freezing and will often decide to stop reading the radios altogether without actually freezing up. A restart of the program or computer we were using the software on would fix these issues. The radios our team was using had never been written to before. The radios come factory set with a 56700 baud rate. The radios had to be read with this rate initially and then written to our baud rate of 9600. This little fact that isn't in the manual took a while to solve.

                Despite these hiccups the software allowed us to configure one radio as the client and one as the server as well as address them to each other. Through several trial and error attempts we were able to use the manual to correctly wire the radio to our arduino and send a test message of "Hello!" several hundred times. From here,  it was a matter of wiring the radio in with the rest of our sensors and main arduino to see if the radios sent all the data we needed them to.

                This caused a few unforeseen problems. The pin which activates the long range mode, pin 11, of the radio needs exactly 3.3V to function. The arduino wasn't providing pin 11 with enough potential when all the other sensors were connected. We got around this by powering this specific pin separately using an external power source and a voltage divider. The nice thing about the potentiometer being used as a voltage divider is that it is adjustable. So if things suddenly change on the day of launch and we need more or less voltage, we can simply change it. The code for our sensors took a little touching up to get the right information and timing to come across through the radio, but we have configured these radios so that the balloon payload will send the measurements to the ground station in real time.