Common Evaluation Pitfalls - Ublox EVK-M101 User Manual

10 Common evaluation pitfalls

• Parameters may have the same name but a different definition. GNSS receivers may have a
similar size, price and power consumption but can still have different functionalities (e.g. no
support for passive antennas, different temperature range). Also, the definitions of Hot, Warm,
and Cold Start times may differ between suppliers.
• Verify design-critical parameters. Try to use identical or at least similar settings when
comparing the GNSS performance of different receivers. Data, which has not been recorded
at the same time and the same place, should not be compared. The satellite constellation, the
number of visible satellites and the sky view might have been different.
• Do not compare momentary measurements. GNSS is a non-deterministic system. The satellite
constellation changes constantly. Atmospheric effects (i.e. dawn and dusk) have an impact
on signal travel time. The position of the GNSS receiver is typically not the same between two
tests. Comparative tests should therefore be conducted in parallel by using one antenna and a
signal splitter; statistical tests shall be run for 24 hours.
• Monitor the carrier-to-noise-ratio (C/N0). The average C/N0 of the high elevation satellites
should be between 40 dBHz and about 50 dBHz. A low C/N0 will result in a prolonged TTFF and
more position drift.
• Try to feed the same signal to all receivers in parallel (i.e. through a splitter) with identical
cable length; the receivers will otherwise not have the same sky view. Even small differences
can have an impact on the speed, accuracy, and power consumption. One additional satellite
can lead to a lower dilution of precision (DOP), less position drift, and lower power consumption.
• When doing reacquisition tests, cover the antenna in order to block the sky view. Do not
unplug the antenna since the u-blox M10 positioning technology continuously performs a noise
calibration on idle channels.
• Be careful not to disable the communication interface while it is been used. The
switch is used to select between UART, I2C or SPI communication interfaces. If the receiver
is set to I2C/UART (option 2) mode and the receiver configuration is saved by sending the
CFG-CFG save command, all input and output protocols for SPI are disabled. Powering up the
EVK in SPI (option 1) mode will result in the receiver starting with all SPI input and output
protocols disabled. Since SPI input has also been disabled, it is impossible to recover using
the SPI interface. Powering up in I2C/UART (option 2) mode and sending a CFG-CFG clear
command restores the SPI interface defaults, which makes the SPI interface usable again for
communication with the receiver.
UBX-21003949 - R04
C1-Public
10 Common evaluation pitfalls
EVK-M101, EVK-M101C - User guide
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