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GPS module evaluation

A project log for Dropsonde Micro

A bite sized dropsonde for taking atmospheric measurements from low to moderate altitude.

Connor HuffineConnor Huffine 02/16/2019 at 00:480 Comments

One of the key measurements I need is windy speed and direction. The most effective method for measuring wind in a sonde situation (where you are moving with the wind) is to measure your displacement. If you drift a certain distance in a certain time, over a certain altitude, the movement of air can be inferred. 

I picked up two low-cost GPS modules from Amazon, a BN-220 (~$17) and a GT-U7 (~$15). They were chosen somewhat arbitrarily, since they should all perform similarly. I tested the two units on my bench. This is indoors, so results are probably worse than they would be outdoors. VisualGPSView was used to display the position and GPS performance information. The GT-U7 has an integrated USB port, while the BN-220 requires an FTDI RS-232 to USB adapter to function with a computer. This doesn't really factor into integrated work, but is an interesting note.

ModelBN-220GT-U7
NetworksGPS, GLONASS, Galileo, BeiDou, QZSS, SBASGPS, GLONASS, QZSS
Fix time15-20s15-20s
FormSmall, integrated boardLarger board, u.fl connector for antenna
Satellites after one hour12 used, 21 in view8 used, 12 in view
Scatterplot

Interestingly, the GT-U7 has a tighter distribution than the BN-220 even with less satellites and a poorer DOP figure. Further tests with the systems outdoors are needed to provide more information, as well as tracking quality under motion.

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