The phase calibration of two USRP(dboard)

Hi, everyone.I am doing the estimation angle of arrival by using USRP.

The problem I want to fix is the initial phase offset of each dboards.

From now on, I have searched some knowledge about this issue. But I can
not implement the concept.

those concept I got are below:

  1. Some kinds of dboard’s initial phase offset can remain constant after
    re-tune by timed command (code)

http://files.ettus.com/manual/page_sync.html

  1. I saw some AOA finding hardware set using another usrp or dboard to
    transmit a reference signal into the USRPs which are receivers connected
    to antenna array elements.
    https://decibel.ni.com/content/docs/DOC-25716

Because the dboards I use is not only one type(SBX), so I prefer to use
the reference signal to do calibration of dboard.

My simple hardware set is below:
Two usrp 2932 (with SBX)
One trimble GPSDO to provide 1PPS and 10MHz

I use GNUradio 3.7.5.1 , UHD_003.008.002-0-unknown

I receive a signal by Two usrps which is connected to ‘one antenna’.
Theoretically, when I plot the I Q data from two usrps, I will get same
waveform(phase). But I get the offset still and I find the offset is not
constant!!

summary of the problems I am suffering:

  1. I do not know where and how to add those ‘timed commands’ which
    taught in the USRP Hardware Driver and USRP Manual.
    (I saw someone said that I can do nothing and the initial offset of SBX
    will remain constant after retuning. But the result tell me it’s not
    true.)

  2. Can anybody provide or teach me the code of phase calibration by
    using another USRP ??? I saw some presentation but there is no source
    code I can learn…
    I try to use the two port (RX1 and RX2) to receive the signals in the
    same time, but I failed.
    I really do not understand how to set the gnuradio blocks to complete
    these work.
    any example could provide to me or anyone can help me??
    (I think I know those concepts and knowledge but I can implement it in
    hardware and software)

thx a lot !!

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