Clock from phone

Alexander Huemer alexander.huemer at xx.vu
Tue Jul 3 13:27:33 UTC 2012


On Tue, Jul 03, 2012 at 03:08:02PM +0200, Dario Lombardo wrote:
> On Tue, Jul 3, 2012 at 1:44 PM, Sylvain Munaut <246tnt at gmail.com> wrote:
> >> In some past post of the ML, I've read that someone was trying to get
> >> the GSM 10MHz clock reference from the motorola phones.
> >> This aimed at feeding usrp with a stable reference, if I'm not wrong.
> >> Anything new this side? This would be extremely useful if GPS signal
> >> can't be got but GSM cell can.
> >
> > 1) It's not 10 MHz but  26 MHz
> 
> Mmm... but the front panel of usrp is fed by 10 MHz/1pps... isn't it?
> 
There are different revisions of the USRP. Sylvain is talking about the
USRP1, you of a later rev.
The USRP1 has an (unpopulated) direct clock input.
The other USRP revisions have a reference clock input, which is
something different.

> > 2) Yes it works, but you can't feed the USRP directly, you need to
> > multiply it by 2 (using a PLL chip) to get 52 MHz for the USRP.
> 
> Can you provide some link to read something about it?
> 
See [1,2,3]
> Don't you think that this way could be much more preferrable than the
> GPS way, if USRP is under GSM coverage? I mean: the clock from GSM is
> next to us... why just don't use it? Probably there's something I'm
> missing, since this approach is much less used than GPS clocking...
> 

There are many ways to provide a stable reference clock. A OCXO (e.g.
[4]), a cheap rubidium standard, the clock tamer[5], ...
Every option has up and downsides.

Kind regards,
-Alexander Huemer

[1]
http://lists.osmocom.org/pipermail/baseband-devel/2010-April/000322.html
[2] http://bb.osmocom.org/trac/wiki/PirelliDPL10#Phoneasclockgenerator
[3] http://sourceforge.net/mailarchive/message.php?msg_id=24642256
[4] http://shop.sysmocom.de/products/ohm4-ocxo
[5] https://code.google.com/p/clock-tamer/




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