Dear Marcus
The problem is solved by setting RF policy manual for RF and DSP both and 
passing uhd::tune_request_t  object as parameter to set_center_freq function, 
but now i getting one more issues that after 35-40 iteration my application is 
getting assertion because of  "EnvironmentError: IOError: Block ctrl 
(CE_00_Port_30) no response packet - AssertionError: bool(buff)" and after that 
I have to start X310 again then only it responds.

My setup is X310 with single TwinRX module and I want to measure the phase 
difference from 10-6000MHz and put into look-up table. I am using B205-mini as 
transmitter and it is connected with the power divider to X310 input. I am 
working on phase interferometer direction finding with 5 element circular array 
antennae connected to 5 to 2 Antenna Switch matrix which is connected to single 
 TwinRX.

I am not sure how  set_center_freq command is implemented internally for 
TwinRX,  but i expect that when i set this command, only LOs should be tuned 
for desired frequencies plus some filter selection of that band. I expect that 
settling time for synthesizer would be around maximum of 300uS and for some 
other stuff like filter selection , i think in  500uS I should be able to set 
everything. At present I have to use set_command_time so that my channels are 
synchronized. Can you suggest the fastest way to implementing frequency sweep 
for two channels as i need scan rate around 40GHz.
Regards,Arun Verma

      From: Marcus D. Leech via USRP-users <usrp-users@lists.ettus.com>
 To: usrp-users@lists.ettus.com 
 Sent: Monday, 17 December 2018 10:36 PM
 Subject: Re: [USRP-users] Phase Offset problem when center frequency is 
changed dynamically
   
 On 12/15/2018 08:02 AM, Arun kumar Verma via USRP-users wrote:
  
  Dear Users 
  I am facing problem of phase offset when i change center frequency 
dynamically for TwinRX with X310 setup. Here is my C++ code, 
  
  Please advise 
                 
usrp_source1->set_rx_lo_source("internal",uhd::usrp::multi_usrp::ALL_LOS,0);
                
usrp_source1->set_rx_lo_source("companion",uhd::usrp::multi_usrp::ALL_LOS,1); 
                  
usrp_sourceDOA1->set_command_time(usrp_sourceDOA1->get_time_now() + 
uhd::time_spec_t(0.01));
                 usrp_sourceDOA1->set_center_freq(m_CenterFrequency,0);
                 usrp_sourceDOA1->set_center_freq(m_CenterFrequency,1);
                 usrp_sourceDOA1->clear_command_time(); 
  I feel set_command_time is not working properly. When i start the X310 my 
phase difference is almost zero but as i change my frequency pjhase difference 
is random in nature. 
  Regards, Arun Verma 
  
 COuld you explain your setup a bit more here.
 
 I now see that you have both usrp_source1 and usrp_sourceDOA1, but I think you 
said that you have a single X310, so I'm confused about
   why you apparently have two USRP sources here.
 
 
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