On 03/07/2018 12:04 PM, Hojoon Yang via USRP-users wrote:

Hi, folks.

In application note from Ettus, "Synchronization and MIMO Capability with USRP Devices",

They said that "Generally, these fractional-N synthesizers introduce a random phase offset after each retune."

What does "random phase offset" mean?

Q1. Does it mean that if I send a signal, Acos(fc*t), then It actually sends the signal Acos(fc*t + "random phase")?

It means that if you have two receivers that are otherwise synchronized (via shared reference clock, and time-aligned via 1PPS), each receiving the same, otherwise-phase-aligned, signal, the two receivers will see the signal with different phase offsets, because the two (or more) LOs are
  not running at exactly the same phase offset.

Q2. After retuning, unless I retune it again, does the random phase offset retain consistently?

Indeed, provided that all the receivers involved are sharing a 10Mhz reference clock, and are time-synchronized, the phase offset will remain more-or-less constant throughout a given "run". I say more-or-less because there is analog circuitry involved and very-fine-scale group delays will shift randomly in different directions in the two pieces of hardware, but this should be very small.


Am I correct?

Thanks in advance.

Regards,



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