NRF9160 KC certification RE test problemn

[hogen]

Hello, my product is undergoing KC certification testing. The required testing bands are LTE-M Band 3 and Band 5. However, the certification company reports that my device is also transmitting signals on other bands (see attached screenshot). They want us to disable the other bands to avoid additional RF testing fees. We contacted the certification company to inquire about their specific testing procedures, and their feedback is as follows:
The certification company is conducting certification tests with itsequipment called CMW500. The equipment is said to perform X frequency tests sequentially from Band 1 to 2, 3~~. The test currently failing is called the Radio Emission Test. It's also known as the RE test. (Rradiation Electromagnetic test)

We tried adding the XBANDLOCK command during application layer initialization, and we found that this command could lock the band for normal network attach. However, the problem persists on the CMW500. The certification test seem to be outside the standard network attach process? Could you please advise on our next steps? Thanks.
AT%%XBANDLOCK=1,\"0000000000000000000000000000000000000000000000000000000000000000000000000000000000010100\"\r\n

[hogen]

To add a bit of information, the modem's firmware version is mfw_nrf9160_1.3.7

[Simon D-M]

Hi,

Sorry, I'm not extremely knowledgeable on RE measurement tests. I've forwarded your issue internally.

For the moment, I see that in your %XBANDLOCK command you have all the zeros before the band that you want to lock. This is not needed, you can have the command %XBANDLOCK 1, "10100" and it would do the same thing. Can you try with the shorter command maybe? And, what was the modem answer when you sent the long command ?

Best regards,

Simon D-M

[hogen]

Hi, thanks for your sugguestion.

The AT command answer is OK. I also query the lock result by command "AT%XBANDLOCK?" after BANDLOCK command, the result show that the configuration has taken effect. 

I haven't tested the short commands yet, as the certification authority charges a fee for each test. However, I've confirmed that the long commands work for network access. For example, I lock the band to 3 and 5. But our operator's actual frequency band is 8, the device can't connect successfully. When I set the band to 3, 5, and 8, it can connect(lte_lc_connect()) successfully.

Best regards,

Hogen

[Simon D-M]

Hi,

hogen said:

The AT command answer is OK. I also query the lock result by command "AT%XBANDLOCK?" after BANDLOCK command, the result show that the configuration has taken effect. 

I haven't tested the short commands yet, as the certification authority charges a fee for each test. However, I've confirmed that the long commands work for network access. For example, I lock the band to 3 and 5. But our operator's actual frequency band is 8, the device can't connect successfully. When I set the band to 3, 5, and 8, it can connect(lte_lc_connect()) successfully.

If the answer was "OK" as you said, It means that the command was indeed taken into account. So it would be the same with the short-form command.

Honestly, I'm not sure to know what your issue is. However, I should soon get an answer from someone internally, and I'll come back to you before the end of the week.

Thank you for your patience.

Best regards,

Simon D-M

[Simon D-M]

Hi Hogen,

Sorry, our expert on that subject is out of office this week. He should come back next week.

I'll keep you updated as soon as I have an answer.

Thank you for your patience, I'm really sorry for the delay. 

Best regards.

Simon D-M

[Simon D-M]

Hi Hogen,

Sorry for the delay.

Our theory on what is happening in your case is the following: The band lock seems to be working fine. But the strange thing is that the problematic frequencies are not on the LTE bands. They possibly are unwanted emissions caused by the harmonics from the board around the nRF9160.

However, there are things that are still unclear:

• Which band and TX frequency was used on the measurement picture you sent ?
• Does the "harmonics" changes when another frequency is used ?

If you can get these questions answered it would be great

Also, if you really think that it is our chip that produce these frequencies, can you please provide some raw modem traces (.mtrace or .bin).

Best regards,

Simon D-M

[hogen]

Thank you for your reply. This issue has been resolved. It was finally found to be a problem with the signaling settings of the CMW500. After modifying the signaling setting of the CMW500, the issue has been resolved.