June 29, 2009
Tutorial - HAB - Sensor System, Flight Computer, and Radio System
about 5 years ago
It’s not surprising that your package stopped updating around 57,000'. The DoD restriction on GPS signals call for the GPS module to stop sending updates if they go above 60,000' and 1,000 knots. Unfortunately, the rule is a bit ambiguous, so a most manufacturers interpret this as “OR.” The Trimble Copernicus is known to work, and the “Inventek High Altitude Build” is also good.
Your antenna could also be another problem. Using a “high gain” omni means that you are flattening out the radiation pattern. This is desirable if you are trying to cover your whole school with WiFi,. but it effectively extends the “cone of silence” underneath the balloon. It’s likely that you could not receive the signals at all if you were within a few miles of it.
Also, you should really consider putting a secondary transmitter on there, so that you can use good-old-fashioned DF (direction finding)to locate the box when the GPS/Computer/etc fail. Power this TX with a separate, non-rechargeable Lithium battery and maybe make it a separate package with a different antenna design.
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