MAX-M8W-0-00 drops satellites

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We are using the MAX-M8W-0-00 with a Taoglas active GPS receiver. The unit gets about 9 active satelites and after a while they suddenly collapse to zero. The numbers collapse to zero in about 10 seconds. On one set of data logs, the unit ran for 1, 2 and 5 minutes before GPS stopped. We have several machines that do this. Testing is done in a field.

We do not think that someone is following us with a jammer.

Is the SW code a clue?

What can we do to isolate this bug?

Best regards,  Tim Orr

 

Hello, 

(Text put in the proper place this time)

We have more observations. We fed the MAX-M8W directly with a generated single satellite GPS signal through a coax cable and a UFL connector. This returned a 36dB S/N ratio. Our board gets hot. As the temperature went from +30C to +50C, the S/N ratio went down by 5dB. Would a temperature rise of this size cause a 5dB degradation? A small blast with freezer stopped it from functioning. I am not certain that a freezer test is valid as it would not happen naturally and freezer can be -50C. 

I could not see temperature mentioned in the data sheet other than the maximum limits. Does anyone have experience of temperature dependencies.

Best regards, Tim Orr

 

Hello, 

What is the sensitivity of the MAX-M8W to noise in the power supply? I could not find any information about this. The 'Migration' document seems to not recommend power supply filtering (with resistors or inductors). The supply is +3.3V which is obtained from a switcher with all of its inherent switching noise. Maybe I should have used local LC filtering for the module. 

The PCB generates about 3 Watts of heat and rapidly warms up. The air temperature inside the unit can reach +40C above ambient temperature.

Best regards,  Tim Orr

 

Hi, another question. When using the MAX-M8W to receive satellite data, what is the range of S/N values that can be expected. That is, the maximum S/N to the minimum S/N for satellite acquisition. I do not have a sense of what is considered good and bad.

Best regards, Tim Orr

 

 

asked Jan 12 by orrcam
edited 2 days ago by orrcam
Check the DC bias on the RF_IN pin in working vs stopped working conditions.
Reset receiver to default via UBX-CFG-CFG, make sure that it isn't in some power saving mode.
Check the stability, ripple and noise level of your source of VCC to MAX.
(Edit) use a scope to look for millisecond or microsecond dropouts on VCC.
Watch UBX-MON-HW to assess changes in  AGC and Jamming indicator.
Hello,

We have more observations. We fed the MAX-M8W directly with a generated single satellite GPS signal through a coax cable and a UFL connector. This returned a 36dB S/N ratio. Our board gets hot. As the temperature went from +30C to +50C, the S/N ratio went down by 5dB. Would a temperature rise of this size cause a 5dB degradation? A small blast with freezer stopped it from functioning. I am not certain that a freezer test is valid as it would not happen naturally and freezer can be -50C.

I could not see temperature mentioned in the data sheet other than the maximum limits. Does anyone have experience of temperature dependencies.

Best regards, Tim Orr
>> Our board gets hot.
In an abnormal fashion?

Check the performance of your supply in these conditions, ie mV level noise in the supply voltage, temperature likely to have an impact to external components.

The part has a TCXO, this should have reasonably consistent operation over temperature (performance see UBX-NAV-CLOCK). The operation limits here are likely -40C to 85C at the device.

See bottom of Table 9
https://www.u-blox.com/sites/default/files/MAX-M8-FW3_DataSheet_%28UBX-15031506%29.pdf

For a direct feed from a simulator via coax 36 dBHz seems rather depressing.

1 Answer

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50 mVpp is what u-blox recommends for power supply ripple.

Under unobstructed view of the sky C/N0 values with good antenna are around 45-50 dB/Hz
answered 1 day ago by grumpy Senior Principal Expert
Hello 'grumpy',

Many thanks for your reply and also to others that have replied. Our 3.3V supply has a noise level of about 15mVpp at  580kHz from a switcher. I will try a Microchip Ripple Blocker to reduce the supply noise. A low noise supply has to better than the output from a switcher.

Best regards,  Tim Orr