This year at Balloon Fest, we wanted to demonstrate a complete wireless setup that was not dependent on the Virtual Classroom, as shown here:

This could allow teachers and students in the S4 program to test their payloads on balloons before they attempt a rocket launch. We believe that a balloon launch to 1,000 ft is something that teachers in the S4 program could likely conduct on campus at their schools. During the experiment we were able to show that the wireless signal strength between the payload attached to the balloon and the ground based ‘off the shelf’ commercial router remained strong enough to continue the real-time transfer of data from the payload to the server. During this field test, we also were successful in debuting our new server model where data is saved to a MySQL database instead of a static text file.

To determine signal strength, a message generated by the WiFly chip was received by the server. This message contained a measurement of the signal strength from the router measured in dBm. This message was assigned a time stamp by the server, and saved to the MySQL database. Later, these messages were correlated with the GPS data from the payload to generate the following graph.

Altitude (m) vs. Signal Strength (dBm)

The launch site was at an altitude of about 300m.

Based on these findings, we are highly confident that the off the shelf WiFi solution will be very reliable for test flights around 1,000 ft. It’s very probable, extrapolating from the data, that flights to higher altitudes would also remain successful.