Re: [Discuss-gnuradio] New external clock board for USRP

[Alexander Chemeris]

Yes, connecting to SPI is an interesting option. We'll consider looking at it.
Is there any documentation for this bus available?

On Mon, Sep 28, 2009 at 20:00, Tim Pearce <address@hidden> wrote:
> In terms of integrating more tightly with the USRP/GnuRadio
>
> You could (maybe) just use the SPI pins and one of the digital IO lines as
> the enable (the ATMega8 running as a slave)
>
> That way theres functions to communicate with the chip already built in you
> just need to define the various commands etc?
>
> Tim.
>
> On Sun, Sep 27, 2009 at 9:53 PM, Alexander Chemeris
> <address@hidden> wrote:
>>
>> Hi Matt,
>>
>> On Fri, Sep 25, 2009 at 05:20, Matt Ettus <address@hidden> wrote:
>> > Alexander Chemeris wrote:
>> >> We're creating a clocking unit which will be easy to use with
>> >> USRP. If there will be enough interest from the community we
>> >> can order some amount of PCBs and put them for sale alone or
>> >> soldered and ready to use. This should be useful for everyone
>> >> trying to run OpenBTS, working with GPS and everyone else
>> >> who need to re-clock their USRP or have more clock precision.
>> >>
>> >> We've created it to run USRP at 52MHz with 0.3-0.5ppm after
>> >> calibrating or 1ppm in long term without recalibrating, but actually
>> >> it will support 2.84-65.83MHz, 65.91-71.82MHz, 72.5-79MHz clock
>> >> ranges with about the same precision.
>> >
>> > I don't know what part you are planning to use for this, but it looks
>> > like a
>> > tunable oscillator, which is likely to have a lot of jitter.  To avoid
>> > problems, you would need something with less than 1 picosecond of
>> > jitter.
>> >  The crystal on there now has about 250 femtoseconds of jitter.
>> >
>> > I would strongly suggest that you use a plain old tcxo, and pick a part
>> > which is available in many different frequencies.  This would result in
>> > a
>> > much cleaner output, and much less complexity.
>>
>> Thank you for your input. Our unit is based on low-noise National's
>> VCO+PLL
>> sourced from precise reference generator. Of course, all phase noises are
>> taken
>> into account. I need to check with my collaborator who're actually doing
>> this
>> work to get exact numbers. I'll post them here a bit later.
>>
>> --
>> Regards,
>> Alexander Chemeris.
>>
>>
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>
>



-- 
Regards,
Alexander Chemeris.

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