I've bought 3G modem EU870D for RB411U as a "DELL 5520 3G modem".
It works "enough", but I need also to know the signal strength (usually through "Info" button of PPP-client interface).
The answer is "modem not responding".
I'm working with "data-channel=0, info-channel=1" (modem has got 2 channels).
Using serial-terminal on channel 0, it answers to AT commands, in channel 1 I haven't any answer from modem.
Ok, maybe it's a "DELL-only" modem, so I've bought a new brand EU850D.
Is the modem not supporting channel 1 (really?) or maybe some bug of Routeros (5.21)?
I'm coming crazy.
If I use an external USB modem (Onda MT833UP), it works correctly, displaying also sognal strength.