Disconnects on T-Mobile 5g

IoT Modules 5G Module
1

Hello,

I’m having a problem with multiple devices having disconnects and requiring our router to power off the modem to reboot to bring connection back up. Logs show

Carrier: T-Mobile
APN: fast.t-mobile.com
Modem: RM520N-GL
Modem Firmware: RM520NGLAAR01A08M4G
Router platform: Mikrotik RouterOS 7.15.3

RSRP is -94 and SINR is 16 and RSRQ is -11.
Connects to Band41 and speeds are good.

When this issue occurs, the LTE interface loses connectivity to the tower but there is no indication on why. The signal level is not very high but also not near a potential disconnect level.

Do you have any ideas on additional logging I could setup to determine why this is happening?

2

Could this be heat related? How would I query the modem to find out if any heat related event has occurred?

3

I don’t know a way to tell after the fact, but if you send

AT+QTEMP

immediately after it happens you should be able to see an elevated temperature.

4

Thanks. I’m logging temperature now but only seeing about a max of 73 on sensors. So it doesn’t seem to be heat related.

Any other suggestions on what I could log to get a reason for these disconnects?

5

Could it be because of insufferable power supply when downloading a large file the modem tries to aggregate two 5G bands or more? You can rule that out by temporarily disabling all 5G bands except N41.

6

Thanks, good idea. I’ll try to find max power draw of the radio and see if it could be overloading the board capability.

7

I’m having similar problems, but in my case the signal is really bad (all carriers in our area are poor, due to NIMBYism blocking the building of any antenna towers near us).

Anyway, I did the research with the help of snowgum, who told me about the official Hardware Design Guide for the modem.
According to the guide, the RM520N-GL draws a max of 3.7V at 5.0A = 18.5W. It requires a minimum of 3.7V at 3.0A continuous current = 11.1W. That’s with no sag in the voltage or current.

As far as I know, no USB to M.2 board puts out a rock-solid steady 3.7V at 3.0A.

I am currently using an MCUZone USB+Ethernet to M.2 board, and it disconnects all the time. I can’t prove that it’s the power supply because the poor signal is always an issue for me, but others here have stopped using the MCUZone boards and said that rework.network boards are better. But even those only claim a max of 10W power supplied to the modem.

I’m hoping that with enough demand, some mfg. will make a board that supplies a clean, rock-solid 20W to the modem to meet all of the modem’s demands.