Hi Christoph! glad to hear that you are experimenting with the sysmoBTS
1002.
First, I'd concur that it could be a clock issue, you should calibrate
it anyway.[1]
In my experience, you can calibrate against an 850 or 1900 network, and
this calibration is valid for all bands. (99.9% sure there is no issue
with that, but somebody else with better knowledge of the OCXO might
correct me)
Although another thing that /might/ be happening is that your phone is
seeing a stronger (or maybe just another) signal from a commercial
network, and is as such trying to attach to (roam on) that network. That
network looks at the IMSI provided (your 99970xxx...) and says, you are
not allowed to attach, go away and be quiet and never try to attach to a
network again (until airplane mode is toggled)
I can't remember off the top of my head what the LUJ cause code is that
does this, but it is an issue.
You can add the PLMNs of the local networks to the SIM card's forbidden
list and this should stop this procedure and you should stay on your
network. Also, if it is a multi band phone, try to restrict it to 2G
only, and of course, place it in manual network selection.
[1] Calibration instructions are in the 1002 Manual, Chapter 13.3 If you
do not have this manual, please reach out to sysmocom.
On 26/08/2025 10:25, Christoph Quirin Lauter wrote:
Hello,
thank you for your answer.
I cannot use a neighbor cell (of a commercial network) I guess because
I doing GSM900 here in the US, while all the commercial networks are
at 850MHz. Or is this an option? If yes, would you please point me to
the right config option?
I do not have the GPS clock option installed. What would it take to
install the option?
Would you mind explaining how recalibration is done?
Thank you!
Christoph Lauter
Joachim Steiger wrote on 26.08.25 at 10:14:
Hi,
you may want to check your clock calibration.
either against a neighbor cell or if installed as option the gps
clock source.
clock calibration is a value stored on the device and can be
overridden in config in case it drifted too far over time.
this is not uncommon since the crystals age with use and time.
a recalibration every few years should be enough in most cases.
the behavior of the phone sounds a lot like what happens if the phone
gets confusing clock-references from the networks it can receive and
at some point decides which one is 'right' and ignores whats not
fitting that raster.
regards
