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_Dist…
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