Hi all, i've purchased a Chaetau LTE 12 and i'm very happy with it. I'm only a little confused by a thing that continuosly happen with the LTE module of the router. When i enable the LTE interface, the router istantly gains max signal and shows that i'm receiving the Primary Band and 2 CA Bands. The speeds are very good (150/170mpbs in download), but after 10 minutes of using, the router starts loosing signal and all the CA Bands remaining only with the primary band. Obviously the speed of the connection decrease a lot (15/20 mbps in download) and i'm constricted to disable/re-enable the LTE interface to regain max speed and resume the CA Bands signal. I'm with RouterOS 7.1 beta (latest one)
Is this an hardware fault or a software problem? Anyone with this problem before? it's very strange...
ISP: Iliad Italy

Sorry for bad english

The question here is probably, why did the router lose signal?
Because operators will not upgrade you back to CA, this is the operator decision. They could configure it to work differently, but your operator hasn't.
Basically if you lose signal or signal gets bad, you will lose CA band and will not get it back. Chateau is not doing this, the operator is.

Okay... maybe in the next days i will change the sim to test with a different operator.
Thanks a lot for your answer!

Is this an hardware fault or a software problem? Anyone with this problem before? it's very strange...
ISP: Iliad Italy

I'm using the Chateau with an old 3 Italia's SIM on Wind3's new network. The 3 CA is always on. Sometimes the primary band switch between B7/B3/B1 but the connection don't drop down.
I'm using 4 external LPDA antennas on the roof because i'm in the country at 1,5km from the bts at the other side of a woods.

Sorry for digging up old posts, but I decided that I should probably write here instead of creating a new one with the same issue.
I have been experiencing the same issue for a long time now with Mikrotik LTE18 modem from Latvian operator LMT. Found this topic a while ago and I can confirm that the loosing CA bands is done from the operator side.
However the root cause why this happens is directly related to the modem and I will try to prove this below. Also please note that in order to have this issue, several conditions have to occur.
1) first of all you have to be reasonable distance away from the tower - just the right amount where you have external antennas, but still you can get very weak signal with internal antenas inside the house (key moment here is weak signal inside)
2) the operator has to drop CA bands when you dont download anything - this happens with LMT but not with Tele2.

Now, after you connect to the tower, modem happily picks up Primary+3CA bands. To monitor signal per antenna, you can run this in terminal: This will output RSRP values each second.
I could not find exact documentation for the values. But my guess is that you get 4 values if you use internal 4x4 MIMO or you get still 4 values, but first 2 are for external antennas and last two are antenna3 and antenna4 inside the modem (probably mimo1 and mimo2).
When everythin is working, you should get an ouput something like this: This indicates than my ext1 and ext2 antenna have RSRP of -95 and -107 ... and both internal antennas are not used, therefore value -140.

I haven't figured out exactly why, but at one point the output starts to look like this: As you can see, suddenly ant3 and ant4 have a signal reading. After a while it goes back to -140. I went into Interfaces->LTE->Modem and can confirm that "External Antenna" is set to "both" and not "auto". I've decided to try disconnecting internal antennas from the board at all so it does not pick up any signal from the tower. While doing so, the output of QRSRP still showed values above -140, however this time the signal was very low:
And exactly at this moment I lost all CA bands.
I did a reset of LTE, got 3CA, then waited for some time for modem to try to use internal antennas again. And it happened exactly the same way - whenever the ant3/ant4 signal changes from -140 to something better, I loose all CA bands.

So why this is happening? Operator tries to optimize the connection by disabling low-signal bands and leaving only ones with good signal. External antennas are doing good untill you dont download anything and tower drops CA. Then (my best guess) modem sees this and thinks that external antennas went bad and "pings" tower through internal antennas. Tower sees that signal is poor and below certain threshold and disables the band.

This should be software fixable. Maybe there already is some AT commands to disable internal antennas completely. Haven't found them yet.
Also this could be fixed on the tower side by lowering the signal treshold however this is not a 100% fix since it really depends how far you are from the tower.

Just 5 cents: in LTE RSRP of -115 is really low value, barely usable - e.g. in normal cell where max throughput when using 2x2 MIMO is 200Mbps, with RSRP of -115 throughputs fall to 10Mbps or similar. Theoretically LTE connection can be alive even at lower RSRP values, it's settable by network operator (some set it to lower just to "fake" larger coverage area). So if antennae needed for CA can only receive signal at such low levels, the effect of CA will be small (or negligible).

I'm not saying that MNO doesn't disable CA for device which had problems with it previously. However, CA only works if device (modem) can measure signal of cells candidates for CA. If modem does not report those, then base station will not schedule transmit slots on secondary cells and modem will know nothing about CA.

It looks like it comes down to 4x4 MIMO kicking in and using both external and internal antennas which triggers dropping of CA bands because of the low signal quality for internal antennas. I don't think 4x4 MIMO can be disabled with AT commands. This seems to be available only for EM160 with AT+QCFG="lte4x4mimo/disable", but there is no such command for EM12/EG12/EG18

any assistance from mikrotik side would be welcome

It looks like it comes down to 4x4 MIMO kicking in ...

could be. LTE in theory supports 4x4 mimo in all bands, but due to physics operators only build cells and enable it on higher bands (2GHz+), often only on TDD cells.

A more likely explanation is that modem uses one pair of antenna ports as 2x2 MIMO for low band (e.g. sub 1.5 GHz) and the other pair of antenna ports as 2x2 MIMO for high band (1.5GHz and upwards). There's logic in exposing only low-band antenna ports outside of device case ... higher frequencies have higher path loss and if signal from cell tower is low enough to require use of external antennae, high-band signal will likely be too low to give good performance even if using external antennae. And then there's the quest for lowering production costs and why install something that rwally few users will use? Not every user will be willing to install 4 external antennae (some try to get away using single external antenna) or to use high quality antenna combiner (which can join low- and high-band antenna port to connect single wide-band antenna).

I might have found a solution to this one: viewtopic.php?t=195376