UBX-17053592 - R03
Early Production Information
Common evaluation pitfalls
Page 31 of 33
10
Common evaluation pitfalls
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Parameter 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, cold start times may differ between suppliers.
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Verify design-critical parameters; do not base a decision on unconfirmed numbers from datasheets.
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Try to use identical or at least similar settings when comparing the GNSS performance of different receivers.
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Data that 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.
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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.
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Monitor the Carrier-To-Noise-Ratio. The average C/No ratio of the high elevation satellites should be between
40 dBHz and about 50 dBHz. A low C/No ratio will result in a prolonged TTFF and more position drift.
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When comparing receivers side by side, make sure that all receivers have the same signal levels. The best way
to achieve this is by using a signal splitter. Comparing results measured with different antenna types (with
different sensitivity) will lead to incorrect conclusions.
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Try to feed the same signal to all receivers in parallel (i.e. through a splitter); the receivers won’t have the same
sky view otherwise. Even small differences can have an impact on speed, accuracy, and power consumption.
One additional satellite can lead to a lower DOP, less position drift, and lower power consumption.
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When doing reacquisition tests, cover the antenna in order to block the sky view. Do not unplug the antenna,
since the u-blox M8 positioning technology continuously performs a noise calibration on idle channels.
