Prototype with nRF9160 does not register on network, returns +CEREG: 0

[EmbeddedDan]

I'm using the Serial_LTE_Modem application (nrf source version, zephyr v2.4.0-ncs1, mcuboot v1.6.99-ncs1, mcumgr v0.1.0-ncs1 ) with version 1.2.3 of the modem firmware.
I programmed the above into the development kit (nRF9160-DK) and can successfully connect to the our local NB-IoT network using the following AT commands:
AT+CFUN=0
OK
AT%XSYSTEMMODE=0,1,0,2
OK
AT%XBANDLOCK=1,"10000000"
OK
AT%XDEEPSEARCH=1
OK
AT+CGDCONT=0,"IP","nbiot.vodacom.za"
OK
AT+COPS=0
OK
AT+CEREG=5
OK
AT+CFUN=21
OK
AT+CPIN="9670"
OK
+CEREG: 2,"5209","0A19790D",9,0,0,"11100000","11100000"
+CEREG: 1,"5209","0A19790D",9,,,"11100000","00000110"       //1 – Registered, home network

When I use the same AT commands on our prototype I get:
+CEREG: 2,"5209","0A19790D",9,0,0,"11100000","11100000"
+CEREG: 0,"5209","0A19790D",9,0,0,"11100000","11100000"     //0 – Not registered. UE is not currently searching

We have checked the signal strength of the prototype hardware using %XRFTEST and is similar to the development kit output.

Any idea why the nRF9160 find the tower but does not register on the network?

[ketiljo]

Hi Danie

Can you share the schematic and gerber files for the board you've made? 

best regards,

Ketil Aas-Johansen

[EmbeddedDan]

0827.Schematic.PDFPCB0A00070_Gerber and NC Drill files.zipPCB0A00070 433MHz Radio_NO IoT variant PCB 3D Drawings.PDF

[ketiljo]

Hi Danie

The layout doesn't show the LTE antenna. Is this an external antenna with a U.FL connector? If so, the components L4, C24 and L5 are not needed as the antenna tuning will take place on the antenna itself.  What happens if you plug the antenna into J1 and remove L4? 

Note if you are using GEN2 modules, C29 must be 4.7 µF, it will not work with 47 µF.

cheers,

Ketil

[EmbeddedDan]

Thank you for looking at this Ketil.

Yes the antenna is an external antenna.  At the moment L4 and C24 are not placed and are shorted with a blob of solder. L5, C25, C26 and C27 are not placed and are open circuit.  We will remove these matching components in the final PCB.

I'm going to change C29 to 4.7uF and give it a try.

[EmbeddedDan]

Hi Ketil

I did not have any success with a 4.7uF capacitor.  Do you belief the issue we are experiencing to be an RF problem?

Signal strength on the nRF9160_DK is: +CESQ: 99,99,255,255,23,57 and on the prototype its: +CESQ: 99,99,255,255,255,255

The local network using band 8 (900Mhz), this is the output with constant carrier at 900MHz (AT%XRFTEST=1,1,8,9000,17,0,4,12,0,0,0,0)

Output with QPSK modulation (AT%XRFTEST=1,1,8,9000,17,0,0,12,0,0,0,0)

Output with BPSK modulation (AT%XRFTEST=1,1,8,9000,17,0,3,12,0,0,0,0)