# The phase calibration of two USRP(dboard)

**URL:** <https://www.ruby-forum.com/t/the-phase-calibration-of-two-usrp-dboard/243447>\
**Category:** GNU Radio\
**Created:** [November 2, 2015, 5:13pm UTC](https://www.ruby-forum.com/t/the-phase-calibration-of-two-usrp-dboard/243447 "2015-11-02T17:13:57Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\
**Post date:** [November 2, 2015, 5:13pm UTC](https://www.ruby-forum.com/t/the-phase-calibration-of-two-usrp-dboard/243447/1 "2015-11-02T17:13:57Z")

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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](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](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 !!