How to send/receive SMS with Unicode (UTF-8/UCS-2) and long SMS (>160 chars) on MikroTik? PDU mode gives “device inactive”

Hi,
I’m using a MikroTik router with an LTE modem (FG621-EA) and I’m trying to correctly handle SMS messaging with Unicode characters and long messages. I’ve run into a few issues that I can’t solve:


1. Receiving SMS with Polish characters (ąęłńśćżźó)

When someone sends me an SMS containing non-ASCII characters, MikroTik shows corrupted text in /tool sms inbox.
It looks like RouterOS is not decoding UCS-2 messages.

Questions:

  • Does MikroTik support receiving UCS-2 SMS properly?

  • If not, is PDU mode the only way to correctly receive and decode Unicode?


2. Sending SMS with Unicode (UTF-16 / UCS-2)

If I send SMS in text mode:

/tool sms send phone="xxx" message="Zażółć gęślą jaźń"

— MikroTik strips or corrupts the characters.
So I tried switching the modem to PDU mode:

/interface lte at-chat lte1 input="AT+CMGF=0"

Then I attempted:

/interface lte at-chat lte1 input="AT+CMGS=XX" (XX is PDU length)

/interface lte at-chat lte1 input="YOUR_PDU_STRING\x1A"

But as soon as I hit enter, MikroTik returns “device inactive” on any SMS attempt.

Questions:

  • Why does the modem become inactive after trying to send PDU ?

  • Is MikroTik blocking PDU mode internally?

  • Is there a known working procedure for sending Unicode SMS via PDU on MikroTik?


3. Sending long SMS (>160 chars)

MikroTik text-mode SMS is limited to 160 chars, so long SMS are returning Body too long error
I assume I need concatenated SMS via UDH (PDU mode), but again — “device inactive”.

Questions:

  • Is PDU the only reliable method for long SMS on MikroTik?

  • Has anyone successfully sent concatenated SMS (UDH) from RouterOS?