Hello Keith,
that you for your help.
I will try to figure out the calibration against a 850 or 1900 network. If you have a sequence of commands or a how-to to give me, that would be great. I do not have the manual.
My phone is a dual-sim phone. The one SIM is a sysmocom SIM that attaches naturally to 999/70. The other one is a commercial SIM. The phone does not have a 2G only mode.
There are two other 2G networks visible to phones at my place: T-Mobile GSM US (which will go away in a couple of months) and Telcel GSM from Mexico. There are 3G, 4G and 5G networks visible as well.
If possible, I would prefer to install a GPS option. I am using GPS for E1 TDM anyway so I would really prefer this. I have a GPS controlled VCO (Leo Bodnar) laying around, if that helps.
Thanks!
Christoph
Keith wrote on 26.08.25 at 11:29:
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