Locking MNC in Quectel EC25 modem

Question

I have a Quectel EC25 modem and I do not plug the SIM card. When I want to set a different technology (2G, 3G, 4G) or different operator (MNC) using the following commands, "servingcell" is still the previous one.

AT+QENG="servingcell"

+QENG: "servingcell","LIMSRV","WCDMA",432,35,5962,9C58AFF,2993,453,1,-57,-11,-,-,-,-,-

OK
AT+COPS=1,2,"43235",0

OK
AT+QENG="servingcell"

+QENG: "servingcell","LIMSRV","WCDMA",432,35,5962,9C58AFF,2993,453,1,-57,-5,-,-,-,-,-

OK
AT+COPS=1,2,"43211",2

OK
AT+QENG="servingcell"

+QENG: "servingcell","LIMSRV","WCDMA",432,35,5962,9C58AFF,2993,453,1,-60,-6,-,-,-,-,-

OK

How can I apply the above locking on the modem? Is there a memory or similar concept which the current serving cell information is stored and I have to reset or clear before/after locking on the MNC or technology? Is there a complementary command to satisfy the locking conditions?

Answer 1

I don't have an EC25 to try myself, but I'm going to provide an answer based on my standard AT commands knowledge.

In abstract, I'm suggesting you to use +COPS only.

In fact, looking to Quectel EC25 AT commands guide, +QENG command description is missing. Googling it I found out that it is a command for enabling enginering mode, and it syntax seems to vary.

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Strategy:

1. Verify the list of supported operators by issuing AT+COPS=?

Its response is provided in the format

+COPS: [list of supported (<stat> ,<oper (in <format>=0)>,,<oper (in <format>=2)>,< AcT>)s][,,(list of supported <mode>s),(list of supported<format>s)]

In which you will see the list currently seen by the device.

Please note that, for every operator, stat can have following values:

0 Unknown
1 Operator available
2 Current operator
3 Operator forbidden

This will be useful later.

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2. Force the manual selection of the operator. It is what you already do:

AT+COPS=1,2,"43211",2

which, according to command description in the guide linked above, means "Force manual operator selection, in numeric format, to operator "43211", with UTRAN technology"

Please note that

• OK might be returned even if the desired network is currently unavailable
• Some time is required after the OK for the actuar registration to the new operator. So, make sure to wait enough time before querying the current status. In the meantime you can also query registration status by issuing AT+CREG?

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3. After waiting enough time after +COPS set command, query new status. You can either

   • Issue read command AT+COPS?, that will provide the information about the current operator
   • Issue test command again, AT+COPS=?, in which the stat parameter for current operator is 2. If it is true for the operator we just forced, everything is ok.