Optimal MCU clock frequency to reduce EMI interference to co-exist GNSS receiver

[David_]

For battery and small size system, STM32WLE5JC is next to a "patch antenna GNSS module", how you think about two choices?

1. Use low MCU clock frequency.  MCU active for LONGER time, then finish the work and go to STOP2 with RTC on.  I believe low MCU freq is less noisy (but noise duration is longer), right?

2. Use high MCU freq.  MCU active for SHORTER time and then STOP2 with RTC on.  I believe high freq is more noise (but noise duration is shorter), right?

TIA

[Tesla DeLorean]

Put the GNSS antenna on the opposite side of the board to ALL the active electronics. 

Shield it the receiver and RF path

The Intermediate Frequencies in the front-end are typically quite low, in the couple of MHz range. GPS Gold Codes are at 1.023 MHz +/- 3 KHz depending on the motion/doppler and local clock bias.

Some receivers have spectrum analyzer modes, so you can see the in-band interference.

I'd probably favour doing stuff quickly, and limiting radio transmit time.

[David_]

Many thanks.  Any idea which brand/model of single frequency standard precision GNSS receiver (the better unit of this grade with stimutanelous five constellations) has spectrum analyzer modes?  OR, it is domain of survey grade receiver?  TIA

[STTwo-32 · Accepted solution]

Hello @David_ 

For More data about GNSS, look at our GNSS Positioning Forum where you may find more help.

Best Regards.

STTwo-32 

[Tesla DeLorean]

Which constellations? The frequency bands and the RF down converters tend to be the limiting factors here. The uBlox 9 and 10 series have spectrum analyzer diagnostics.

GLONASS is seen to be in decline.

GPS, GALILEO, SBAS, QZSS share signals in the same band. I think BEIDOU has a band on GPS L1 now too.

BEIDOU is seen to be ascendant

GPS will have L1 / L5 dual band will be completely live soon 

NAVIC L5 being pushed hard in India

[David_]

Many thanks.  Plan to use ublox M10, GPS, Galileo, Glonass, Beidou, SBAS, all L1 band.  M10Q has LNA and SAW filter before antenna.  SAW help cut out of band signal.   They are designed to use with cellular phone which is a powerful intentional transmitter.  MCU is un-intentional and weaker but since GPS is -165 dBm, still very weak.  TIA