Manually choosing LTE CAT M bands for testing antenna strength

[SidAHakim]

Hi, 

We would like to test the signal strength capabilities of our LTE antenna connected to NRF9160s. Ideally for this test, we want to be able to only connect to a spcefic LTE frequency band, check the signal strength, and perform the same test again for a different band. We are on the latest connect SDK version. We use a soracom sim card. 

Kindly let us know if above is possible, and what AT commands/Nordic specific commands/Libraries we can use. 

Thanks, 

Sid

[dejans]

Hi,

There are AT commands described in our documentation which could be used for your intended purpose - %XBANDLOCK and %CONEVAL.

Best regards,
Dejan

[SidAHakim]

Hello, 

Thank you for the answer. We have successfully used %XBANDLOCK to restrict the device to connect to only a desired band. However, here in Vancouver, Canada, we have only been able to reliably establish an LTE connection on band 12, send data back and forth to the server, and our Antenna manufacturer is using that to verify the antenna quality on band 12. 

However, we still have not been able to test any of the other bands yet, as our connection times out on those bands, and we can not send any data to our server to test. 

My question is, how can we test the ability of the antenna on a specific band when an LTE connection can not be established. Is there a way to put the radio into some kind of "compliance mode" to do such?

We have also briefly looked into what %CONEVAL is. But we are not sure exactly how to use that for our specific issue (with our limited knowledge on this matter). Any further sugestions regarding this is much appreciated.

We have also found %XRFTEST In the documentation. If the RF transmitter is set to a TX mode with this command, will it contineously transmit up untilll it is disabled?

Best regards, 
Sid

[dejans]

Hi Sid,

It is not possible to put the radio into non-compliance mode in a live network. The best way for antenna testing would be to use antenna lab with call box tester providing signaling over the air.
Non-signaling %XRFTEST command can be used as well, but you would need to have either signal analyzer or signal generator.
There is a white paper nrf9160 antenna and RF interface guidelines which provides general guidelines with regard to antenna, RF testing and control.

Best regards,
Dejan

[SidAHakim]

Hello Dejan,

Thank you for the reply. We want to use %XRFTEST. We have gone over the documentation. We still have a few questions related to it.

Tx mode:

1. If operation on is set by the AT command, will it continue to transmit up until off command is set?
2. When the AT command is run, what kind of signal are we expected to pick up with a signal analyzer? Does it contain any data?

Rx mode:

1. Can you provide a general idea of the test procedure? Is the 9160 going to pick up a signal created by the signal generator?

2. Is the output value of the AT command the only way to read the result of the test? 

Both TX and Rx:

1. The XRFTEST  documentation says:

%XRFTEST cannot be used if the modem has already been activated with the %CFUN command.

To verify this, we have first set the modem to CFUN=1 first and got error. However if we do CFUN=4 before running XRFTEST, we do not get any errors. But in the CFUN documentation it says -

(CFUN) 4 – Sets the device to flight mode. Disables both transmit and receive RF circuits and deactivates LTE and GNSS services.

So question is, If CFUN 4 Disables both transmit and receive RF circuits does XRFTEST still work because our understanding says the XRFTEST command transmits/receives signal?

Best, 

Sid

[dejans]

Hi Sid,

You can get more information about testing RF performance in the documentation. Several test setup cases are described in modem RF functionality section. Additional information can be found in Rx functionality test, Tx functionality test and GPS functionality test.

Best regards,
Dejan