nRF9160 SIBA unable to connect to NB-IoT network and resets every ~10 seconds.

[elephant]

nRF9160 SIBA on custom board is unable to connect to NB-IOT and resets after about 10 seconds of operation.

Without a call to lte_lc_init_and_connect the reset does not happen.

The power, as suggested in other topics is at 2.6V from dc power supply with limit set to 1A.

Side note: this setting is the only one allowing for the programmer to reach the SiP. At planned 3.3V the programmer is not able to connect to the chip. For now just a missing power IC -> power supply is used.

[elephant]

This is the current PCB. No parts below, so not showing the other side. It is 4 layered with internal layers be ground and power polygons.

Current matching circuit has 15nH coil parallel to 0.3pF and 0.1pF capacitors next to antenna, then 2.4nF capacitor in series to wire, then via microstrip to nRF9160. I already did a test with 3Ghz specturm analyser connected via 50 Ohm coaxial cable soldered close to nRF (you can see bare metal there). This setup is picking 845MHz signal from Thingy:91 at a nice -10dB level surrounded by -50dB ambient noise. Can do more tests if needed.

This is the schematics of powering. Vdd = 3.3V Just in case

Now struggling to make segger RTT show up in terminal.

[elephant]

Just got RTT working. mqtt_simple says "failed to establish lte connection: -116" and then "... -120". Already tuned the sample to use only nb-iot as per the chip.

[elephant]

I am curious about two things by now. Is pin 57 really important for RF part of chip to work well? (it is MIPI VIO, not connected in my design)

And is antenna really mechanically symmetric, but electrically not? (As stated by Fractus antennas)

[JONATHAN LL]

pin 57 (VIO) is not curtail for RF operation. It is OK to have it floating. 


Error message  -116 (ETIMEDOUT) and  -120 (EALREADY) 

It is some sort of Time Out and it might be because it cant find a network, bad connection or a error with the SIM card or the SIM service/Subscription.

As for the comment on the antenna symmetry I am not 100% sure what you mean. Do you have a report from Fractus antennas on your board\layout or are you referring to the specs of the antenna? 

Regards,
Jonathan

[elephant]

Yes, to me it also looks like the devices is unable to find network. But the cellular tower is just about 20m away and I am working right next to the window. So the signal strength must be great and enough.

As for the symmetry of the antenna. Seen a note on that once in the documentation for fr01-S4-210, used in Thingy:91. Think this is no issue for nn03-310 used in my design, because no such notes in datasheet.