LTE RF transmission path test AT Command

IoT Modules MC/EM Series
1

Hi,

My EM7430 and EM7455 need to test TX signal with AT command.
I only found below information in the documents without any about LTE RF transmission examples.

There is an example about LTE RF test, but it’s about RSSI not RF transmission.
May someone help me?
Thanks.

BRs,
Allen

2

Allen,

The below sequence works. There are some points about it

  1. Tx and Rx bandwidth need to be set and not just the Tx one. Additionally for this you need to set the right number of resource blocks (RB) in the waveform command as per the attached.
  2. You need to use revision 3 of the AT command spec on the source as some of the commands have been added here.
  3. The power is set by the at!dalstxpwr command which is not specified in the above document although I suspect it takes the same format as the at!dawstxpwr command.

AT!DAFTMACT
290300
OK
AT!DASBAND=42
0
OK
AT!DALSTXBW=3
OK
AT!DALSRXBW=3
OK
AT!DASCHAN=20175
19968
OK
AT!DALSTXMOD=0
OK
AT!DALSWAVEFORM=1,50,10,0
OK
AT!DALSNSVAL=1
OK
AT!DASTXON
OK
AT!DALSTXPWR=1,10
OK

If any of the parameters are wrong i.e. there is a conflict around the wrong combination of parameters there is no error checking on this and the unit will power cycle as the signalling software rejects it, not ideal but that is the way it works, not like you would see this in the field.

Hopefully that helps.

Regards

Matt

3

Hi,

I need to create a script that turns on and off the transmission in selected frequencies / channels, for compliance purposes. The only documentation that I have is the AT command reference (Rev. 3), which is not very detailed in this matter.

Do you have any further information?

I tried to follow your example, and I get an error on

AT!DALSTXMOD=0

And I don’t have information in the AT command reference about AT!DALSTXPWR.

Where did you find this command?

My module is EM7455.

Thanks.

4

Hi,

As the name of these commands implies they are intended for use in a factory to check antenna connectivity, they are NOT intended for use with compliance testing.

For compliance testing you need to use an LTE test set and use this to command the unit to setup the bearer as required. If you use the factory commands it is likely you will see unwanted results as the unit is not being used the way it has been designed or will actually operate i.e. with full power control on a properly modulated/demodulated signal. If you are using a test house that does not have the relevant test equipment to do this I would suggest you change test houses as they are most likely not capable of carrying out the testing as required by the standards anyway.

Regards

Matt

5

Hi Matt,

Thank you for your reply. The test house we are working with has all the bells and whistles to test cellular communications.

The problem is that we need to eliminate harmonics from the LTE, and for that we need to force the module to transmit in certain frequencies.

Regards.

Alexandre

6

Alexandre,

In which case the test house in question can configure the LTE test equipment to work only on the frequencies that you (or they) need it to. Alternatively, assuming you are using the QMI interface, you can force the unit to lock to a cell using the API’s (you cannot do this with AT commands).

Regards

Matt

7

Hi Matt,

I followed your command sequence

and I’m getting an error. Here are the results:

AT!DAFTMACT
OK

AT!DASBAND=42
0
OK

AT!DALSTXBW=3
OK

AT!DALSRXBW=3
OK

AT!DASCHAN=20175
19968
OK

AT!DALSTXMOD=0
ERROR

AT!DALSWAVEFORM=1,50,10,0
OK

AT!DALSNSVAL=1
ERROR

AT!DASTXON
OK

AT!DALSTXPWR=1,10
ERROR

Can you give me an hint to troubleshoot? My module is EM7455.

Best regards.

Alexandre.

8

Alexandre,

I have tried your commands and they seem to come back ok for me. Couple of things to try.

  • Make sure you are using a recent firmware version from the table on the source.
  • Send the at!entercnd=“A710” command before all of the other to make sure they are all unlocked.

Otherwise the commands look ok to me.

Regards

Matt