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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