Can i compensate the frequency offset without using an external signal generator

Hi, all,
I am using two USRP N210 to estimate the channel impulse response. I
sent a 63-PN sequence at 1M sample rate and at 850MHz on one usrp.
Another one receives the signal at 850MHz and at 1M sample rate.However,
i found the received PN signal has frequency offset which can be seen
from the plot of the phase. I have attached the plot of the phase of the
received signal. After calculation, I thought the offset would be 397HZ.
So i tried to compensate the received signal by a complex signal with a
frequency of 397Hz. The workflow is shown in the grc. But this does not
eliminate the frequency offset. Anyone has some suggestions? Thanks a