Clock from phone

Dario Lombardo dario.lombardo.ml at gmail.com
Tue Jul 3 16:18:20 UTC 2012


On Tue, Jul 3, 2012 at 3:27 PM, Alexander Huemer <alexander.huemer at xx.vu> wrote:
> 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.
>

You are definitly right. I was taling about N210, which can be fed by
reference clock input.

>> > 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.
>

Just the "pirelli" way uses clock from existing GSM network.
As said before I think that "reusing" the clock from network could be
very useful, but I don't know if it is more difficult than generate
the signal itself.
Is that possible using motorola phones? Did anyone investigate that possibility?




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