[USRP-users] WBX V3 step size

Marcus D. Leech mleech at ripnet.com
Mon Sep 1 12:03:45 EDT 2014

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.

>  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.

> 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.

> --
> Bob
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Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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