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Tips and questions relating to the GPS modules from SFE
By Ludde
According to the spec of the EM-406A SiRF III and ETek GPS 5Hz Receiver they can operate under conditions with >4G vibrations.

Im just curious, what is the techincal reason for this?

Why is the signal distorted by vibrations?

By jasonharper
I doubt that the vibration spec has anything to do with signal distortion: it has to do with the module not physically falling apart under the stress.
By Ludde
I did 2 unsuccessfull flight tests with GPS unit (EM-406A SiRF III) on my UAV project. The GPS lost satelitte lock 60% of the time and when it worked it only connected to 3-5 satelittes. On the ground I got 7-9 satelittes.

However after inserting some rubber foam around the GPS units, the 3rd flighttest worked 100% of the time with 8-9 satelittes.

Question is, why? :-)
By oPossum
The quartz crystal on the GPS receiver may have been affected by the vibration. A precise clock is needed to lock onto the satellites.
By Cannibal
Vibrations aren't so much a problem for the signal as they are for the oscillator.

Since the oscillator is a physical piece of quartz, vibrations can disturb or damage it. At lower vibration levels the timing jitter of the crystal is affected which decreases the effective SNR or the signals by smearing the spectrum of the oscillator and mixing out of band noise into the carrier.

At higher vibration levels it could do physical damage.
By Ludde