On 05/02/2018 12:32 AM, Hojoon Yang via USRP-users wrote:
Hi, all.
In manual, I see the following sentece.
"The GPSDO improves the accuracy of the internal frequency reference
to 20 ppb, or 0.1 ppb if the GPS is synchronized to the GPS
constellation."[1]
It said 0.1 ppb if the GPS synchronized. However, in the below table,
Frequency Accuracy is +-0.01ppb.
Question: 0.1 ppb vs 0.01 ppb. what is right?
[1]https://kb.ettus.com/X300/X310
Not sure precisely where those numbers come from.
The Allan Deviation for a typical OCXO-based GPSDO is somewhere in the
ballpark of 1.0e-11, at approximately 1000s integration time.
Whether at any given moment, you're getting 1.0e-10 or 1.0e-11 isn't
going to make much difference for the overwhelming majority
of applications.
Most telecom type applications have built-in frequency-offset
compensation algorithms in the receiver code to cope with offsets well
into the 1PPM or worse, range. Some applications, like TDMA with
tight timing, may require better, which is why external-clocking
options are offered.
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