EM7565 can't register on B41 _LTE channel_ 41094

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joshhighley
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EM7565 can't register on B41 _LTE channel_ 41094

Post by joshhighley » Wed May 12, 2021 12:20 pm

I've been using an em7565 with Mobile Beacon (Sprint) on band 41 for several years with no issues (except for a week of Sprint -> TMo changeover). I'm a mile from the tower with LOS so I get a good signal. I use a couple of small panel antennas mounted outside with 10ft cables into my garage where the modem lives in a USB3 enclosure connected to a CBA850.

A couple of months ago, I suddenly lost internet. I moved to the sim card back to the original hotspot and confirmed I still had working service.

After a _lot_ of debugging I found that my 7565 was connecting to a different lte channel than the hotspot and when it connected to the 'bad' channel 41094, the modem couldn't register -- it cycles between EMM and RRC states:

at!gstatus?

!GSTATUS:
Current Time: 356 Temperature: 26
Reset Counter: 1 Mode: ONLINE
System mode: LTE PS state: Attached
LTE band: B41 LTE bw: 20 MHz
LTE Rx chan: 41094 LTE Tx chan: 41094
LTE SCC1 state:NOT ASSIGNED
LTE SCC2 state:NOT ASSIGNED
LTE SCC3 state:NOT ASSIGNED
LTE SCC4 state:NOT ASSIGNED
EMM state: SR Initiated ---
RRC state: Waiting RRC Cfm

IMS reg state: No Srv

PCC RxM RSSI: -68 PCC RxM RSRP: -97
PCC RxD RSSI: -72 PCC RxD RSRP: -101
Tx Power: -- TAC: a503 (42243)
RSRQ (dB): -8.4 Cell ID: 04d4fe31 (81067569)
SINR (dB): 23.6


at!gstatus?

!GSTATUS:
Current Time: 427 Temperature: 26
Reset Counter: 1 Mode: ONLINE
System mode: LTE PS state: Attached
LTE band: B41 LTE bw: 20 MHz
LTE Rx chan: 41094 LTE Tx chan: 41094
LTE SCC1 state:NOT ASSIGNED
LTE SCC2 state:NOT ASSIGNED
LTE SCC3 state:NOT ASSIGNED
LTE SCC4 state:NOT ASSIGNED
EMM state: Registered Normal Service
RRC state: RRC Idle

IMS reg state: No Srv

PCC RxM RSSI: -67 PCC RxM RSRP: -97
PCC RxD RSSI: -70 PCC RxD RSRP: -101
Tx Power: -- TAC: a503 (42243)
RSRQ (dB): -10.0 Cell ID: 04d4fe31 (81067569)
SINR (dB): 22.6

I updated to the latest firmware but it didn't help. In my garage, I unhooked my panel antennas and used a couple of whip antennas on the enclosure. Most of the time, this seems to avoid channel 41094, and uses 41292 and/or 41490 instead. Occasionally, it will still connect to 41094 even with the whips but a reboot seems to fix that most of the time. Reboots did not fix the issue when using panel antennas. Maybe slight signal strength differences?

Here's a working connection with the whip antennas:

at!gstatus?

!GSTATUS:
Current Time: 562 Temperature: 32
Reset Counter: 1 Mode: ONLINE
System mode: LTE PS state: Attached
LTE band: B41 LTE bw: 20 MHz
LTE Rx chan: 41292 LTE Tx chan: 41292
LTE SCC1 state:ACTIVE LTE SCC1 band: B41
LTE SCC1 bw : 20 MHz LTE SCC1 chan: 41490
LTE SCC2 state:NOT ASSIGNED
LTE SCC3 state:NOT ASSIGNED
LTE SCC4 state:NOT ASSIGNED
EMM state: Registered Normal Service
RRC state: RRC Connected

IMS reg state: No Srv

PCC RxM RSSI: -71 PCC RxM RSRP: -101
PCC RxD RSSI: -65 PCC RxD RSRP: -93
SCC1 RxM RSSI: -76 SCC1 RxM RSRP: -104
SCC1 RxD RSSI: -66 SCC1 RxD RSRP: -93
Tx Power: 12 TAC: a503 (42243)
RSRQ (dB): -8.2 Cell ID: 04d4fe39 (81067577)
SINR (dB): 12.8

I have so many questions.
What do the EMM state and RRC state error messages indicate?
Is there any way I can lock the 7565 to channels (similar to band locking) or some other way to avoid 41094?
Why is just 1 channel be having this issue? Why do the antennas make a difference?

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