On 04/06/2021 15:02, Joachim Steiger wrote:

hi

limesdr mini does not have a onboard-clock which is good (precise) enough for gsm requirements. there is no input which can easily be used with an external source like a gpsdo. thus there is no realistic way to reliably do gsm with the -mini, sorry.

External clock can be enabled with LimeSDR Mini, but requires moving (soldering) a 0R link and then you always have to use external clock. Daniel Estevez put together a nice write-up:

https://destevez.net/2019/11/using-an-external-reference-with-the-limesdr-mi...

Supreeth Herle has also created an LMS API port of Kalibrate, that can be used to calculate and update VCTCXO DAC value in EEPROM:

https://github.com/myriadrf/kalibrate-lms

This is obviously not as good as having a GPSDO or similar, but may help.

Andrew

On 04/06/2021 09:53, Akib Sayyed wrote:

I think problem is not with clock

Cause i tuned to tx freq i see no signal

But when i comment ramp code from osmobts i do get signal.

Hi Akib, the lime-mini has low RF power output and it you have the "wrong" settings for tx power or power reduction you may not see any RF signal at all from the mini.

Rather than speculating on such things. you will probably get much better results by following Pau's advice and posting at the very least, your config files for the osmo-* daemons (especially osmo-bsc, osmo-bts-trx and and osmo-trx-lms)

The log output from those program will also be very useful to anybody who might help.

As an extra plus, If you can, capture the traffic beween these programs with tcpdump and also attach this pcap. But not to this mailing list! Do not attach files here! - better to create a ticket on osmocom.org, or if for some reason that is problematic, make your configs pcap and logs available some other way by hosting them someplace and posting links to them here.

k.

Hi Harald,

On 04/06/2021 20:15, Harald Welte wrote:

Hi Andrew,

On Fri, Jun 04, 2021 at 02:38:06PM +0000, Andrew Back wrote:

...

...

limesdr mini does not have a onboard-clock which is good (precise) enough for gsm requirements. there is no input which can easily be used with an external source like a gpsdo. thus there is no realistic way to reliably do gsm with the -mini, sorry.

External clock can be enabled with LimeSDR Mini, but requires moving (soldering) a 0R link and then you always have to use external clock.

yes,that is possible. I tried that, too, some years ago. The bigger problem, as far as I recall, are the extremely stringent clock jitter requirements at this input. There's no on-board PLL anymore, but it was directly the sampling clock of the ADC, right?

Yes, there is no phase detector and ideally the input should be a square wave. There are some more details on the MyriadRF wiki:

https://wiki.myriadrf.org/LimeSDR-Mini_v1.2_hardware_description#Clock_Distr...

In any case, at least as I recall, I didn't manage to get a spec compliant GSM signal out of the LineSDR-mini with that approach using the clocks I had at my disposal at the time.

But in any case, that jitter / phase noise is mostly a conformance related topic and the signal definitely would be good enough to be properly decoded by commercial UE, particularly in a lab setup with otherwise near ideal conditions.

Sure, for best performance would recommend using the larger LimeSDR-USB or a LimeNET Micro, as Joachim suggested. However, you can use an external reference with LimeSDR Mini and this may provide some performance improvement, but with caveats.

Regards,

Andrew