[USRP-users] WBX V3 step size

bob wole bnwole at gmail.com
Tue Sep 2 14:18:40 EDT 2014


Hi Marcus D. Leech and Marcus Muller,

Thanks to both of you for your response.



> On 09/01/2014 11:31 AM, bob wole via USRP-users wrote:
> > Hi,
> >
> > A few questions related two Ettus hardware:
> >
> > 1)  I want to know that what is the frequency step size of the WBX V3
> > LO ?
> My recollection is that it's on the order of a few hundred Hz, but look
> at the driver source code to get a definitive answer.
>
> Thanks Muller pointed out the code and I am looking into it.


> >  2) if I install GPSDOs on two USRPN210 with WBX then would there be
> > any frequency offset between two USRPs ?
> Yes, there will be *some*.  GPSDOs operate by locking a local
> high-quality oscillator to the GPS signals, but they'll never perfectly
> agree on
>    phase and frequency. I'd expect the disagreement to be on the order
> of a few ppb.
>
> > 3) What would be the GPS timing mismatch of the USRPs with GPSDOs
> > installed?
> If you're referring to time-of-day, most GPSDOs produce a 1PPS pulse
> that is +/- perhaps 10ns, and sometimes worse.
>
> Yes, I was referring to time-of-day.

> 4) What happens if I disconnect the GPSDO antennas from the devices
> > after correct GPS time latches, would the time of USRPs starts
> > drifting away? if yes how fastly ?
> >
> A GPSDO builds up a drift estimator, and will continue to use that
> estimator when the GPS sky signal goes away.  Those estimates will get
> worse over time, and definitely if the unit is moved to a different
> temperature environment.  How long will this take?  Hard to say--if the
> thermal environment is stable,
> likely several hours before there's significant skew between any two
> GPSDO that have had their antennae removed.
>
> Thanks again for your detailed answer.

--
Bob
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