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MikeyJ
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Joined: Sun Jan 23, 2022 7:52 pm

RBM33G + Quectel EP-06 - cell preference possible?

Wed Aug 31, 2022 3:04 pm

Hi, maybe someone can guide me how to deal with following issue.
I've been running the Quectel EP-06 with an RBM33G for almost 2 weeks without any problems but yesterday. It's been a very stable 2xCA (B3+B20) connection without any configuration, which seems to have been picked by Quectel preference itself. It just worked out of the box in ROSv7 - I only needed to turn off the USB3.0 mode of the Quectel modem, nothing else. The modem itself is a EP06-E model with a EP06ELAR04A04M4G firmware.
Yesterday, after discovering that there are more LTE cells to try out in my area, I was curious and rotated the LTE antenna - but quickly reverted back to my "working configuration" and antenna orientation due to signal quality issues.
To my big surprise, the Quectel no longer automatically connects to B3+B20 which it was originally connecting to and chooses some nearby B20 cell, which it wasn't doing before. Sometimes it only sees the original B3, but will not add B20 to it as it was doing automatically and very quickly, unless I specifically tell it to do so via cell-lock AT command. I have not come to a conclusion why it does this - I suppose the only reason it could be that the modem is extremely sensitive to antenna positioning.
Finally, I've managed to get B3+B20 running again, but it involves several steps after boot which I have scripted:
- disable LTE1 interface
- set cell-lock via AT command
- enable LTE1 interface
- disable LTE1
- enable LTE1
- result: stable B3+B20
It's interesting that after cell-lock and enabling the modem, I acquire IP address + 2xCA, etc., but the connection is dead - I literally need to disable + enable again as the last step (see above) before it switches to fully working state and connection is working and fully stable.
So, I've figured out how to get my B3+B20 again.
But the issue is, as the title says, is it possible to tell Quectel modem to have a preference for cells/bands? Because today the operator was performing a maintenance on these very specific B3+B20 cell towers, they went offline for two hours, and guess what - LTE1 interface link was down too.
Without cell-lock, the modem would automatically pickup a neighbour cell.
So I'm just asking if it's possible (I can script it but it's not a preferred solution) to have the Quectel modem have a preference for my cells but when it goes down, it will choose something else. With the fixed lock here I just need to wait till my preferred cells go online again.
Thanks for any comments in advance, I really appreciate your experience.

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