USRP N210 WBX phase offset did not remain constant

[chiyofivetimes]

Hello, 

Following  is anouced; 

 After tuning the RF front-ends, each local oscillator may have a random phase offset due to the dividers in the VCO/PLL chains. This offset will remain constant after the device has been initialized, and will remain constant until the device is closed or re-tuned.

However, 

I found the phase offset did not remain constant for some USRP N210 with WBX in for USRP N2x0 receivers synchronized system for 20 minutes. 

I am trying to build phase synchronized measurement system using USRP N200 x 2, N210 x 2 OCTOCLOCK . 

ch1 and ch2 is connected with MIMO cable

ch3 and ch4 is connected with MIMO cable 

ch2 and ch4 is connected OCTCLOCK  wiith  10MHz and PPS. 

All inputs were coupled to SG not sincronized output. 

attached screen shot shows the results observed for 200 minutes. . 

Right end Plot shows drift of phase offset  during 200 minutes ;  white line is ch2-ch1 , red line is ch3-ch1,  green line is ch4-ch1.

It seems each MIMO pair has kept the same phase offset but diffreent  MIMO pairs.

Is this expected results?

Below is the configulation in LabVIEW Block diagram.

  

[chiyofivetimes · Accepted solution]

I have tried following example, and found my USPR N210 WBX pahse offset remain constant.

http://forums.ni.com/t5/USRP-Software-Radio/USRP-Time-and-phase-synchronization-for-source-localizat...

My vi may be  something wrong.

Sorry for posting the wrong infromation because of my misunderstanding.

After resolving my Vi mistakes, I will show them.

[chiyofivetimes]

Here is the results of 4ch phase measurement for 1000 seconds.

ch         reference  Clock     TX/RX       RX  

1ch   MIMO                          SG           E100

2ch   Ext octaclock              SG           

3ch   MIMO                          SG           E100

4ch   Extr octaclock             SG

1ch and 3ch are connected E100 output which frequency 915. 18 MHz

1ch , 2ch , 3ch and 4ch are connetcted SG  which frequency 915.66MHz

All phase are stable  arround +/- 2 degree.

Vi will be attached soon.

[chiyofivetimes]

Here is sources.

[foxhound73]

Thanks chiyofivetimes!

[chiyofivetimes]

I found unstable phenomena occurs in the condtion that  NI_USPR set time.vi  applying timestamp "Now" . 

[chiyofivetimes]

Here is a unstable phenomena. 

As my first message,   MIMO pair ch1 and ch2 are stable and ch3 and ch4 are drifting.

And, 3-1 dphase cal  and 4-1 dphase cal are changing around 100deg periodically. 

Could somebody explain the reason?