On 2025-06-04 09:12, Frederik Zumegen wrote:
Dear usrp-users,
I am working with a USRP X410 model to receive OFDM signals on all
four channels. I am also using a ULA as my radiating elements
(antennas). From the received signal, I wish to acquire AoA
information based on the phase of the channel estimates that I compute
from the received known OFDM symbols.
My first question is: must I set up a phase calibration procedure
manually, like this application note
<https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices> suggests,
to calibrate the phase offsets between all four Rx channels? Or does
the X410 have a built-in procedure that can calibrate the phase
offsets between channels?
Second: can someone explain to me which parts of the RF frontend cause
the phase offset between channels? I have so far tried to understand
the frontend based on the ZBX circuit diagram
<https://files.ettus.com/manual/page_zbx.html>.
Third: can someone point me to resources that present an
implementation for a manual phase calibration procedure for the X410,
if needed?
I appreciate any help or shared experiences on this matter.
Best regards,
Frederik
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Phase offsets can be introduced by both the synthesizers and mixers and
the internal path-lengths in the design of the ZBX.
In *addition* the RFSOC itself CAN introduce phase-offsets, due to
clocking of the ADC.
I don't know to what extent this has all been taken care of at this
point -- my recollection is that early UHD for X410 did not provide for
multi-channel
phase coherence, but I believe that has all been implemented now,
BUT, that may not include phase-offset guarantees. The design has multiple
conversion stages (the ZBX and ultimately the RFSoC), and making sure
that phase offsets are zero becomes quite a bit more complicated when you
add more stages of mixers and synthesizers.
I have a query in internally on this.
Cheers
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