EVK-M8GZOE User Guide
UBX-16030132 - R04
Troubleshooting
Page 27 of 30
requirements. However, the “Position within Limits” flag of the UBX-NAV-STATUS message
indicates whether the configured thresholds (i.e. P Accuracy Mask and PDOP) are exceeded.
TTFF times at start-up are much longer than specified
At startup (after the first position fix), the GNSS receiver performs an RTC calibration to have an
accurate internal time source. A calibrated RTC is required to achieve minimal startup time.
Before shutting down the receiver externally, check the status in MON-HW in field “Real Time Clock
Status”. Do not shut down the receiver if the RTC is not calibrated.
The EVK-M8GZOE does not meet the TTFF specification
Make sure the antenna has a good sky view. An obstructed view leads to prolonged startup times. In
a well-designed system, the average of the C/No ratio of high elevation satellites should be in the
range of 40 dBHz to about 50 dBHz. With a standard off-the-shelf active antenna, 47 dBHz should
easily be achieved. Low C/No values lead to a prolonged startup time.
The EVK-M8GZOE does not work properly when connected with a GNSS simulator
There is RF-input for simulator signal (passive).
When using an EVK together with a GNSS simulator, pay attention to proper handling of the EVK. A
GNSS receiver is designed for real-life use, i.e. time is always moving forward. By using a GNSS
simulator, the user can change scenarios, which enables jumping backwards in time. This can have
serious side effects on the performance of GNSS receivers.
The solution is to configure GPS week rollover to 1200 (as indicated in Figure 11), which corresponds
to Jan 2003. Then, issue the cold start command before every simulator test to avoid receiver
confusion due to the time jumps.
Figure 11: Configuration instruction for using the EVK with a GNSS simulator
The EVK-M8GZOE does not preserve the configuration when power is cut off
u-blox M8 GNSS technology uses a slightly different concept than most other GNSS receivers do.
Settings are initially stored to volatile memory. In order to save them permanently, sending a second
command is required. This allows testing the new settings and reverting to the old settings by
resetting the receiver if the new settings aren’t good. This provides safety, as it is no longer possible
to accidentally program a bad configuration (e.g. disabling the main communication port).
