About USRP's reference input and LED"E" on front panel

[iygu]

Hi, I have 2 questions.

I'm just trying to recieve continuous wave(CW) from signal generator by USRP 2920 and LabVIEW program(attachement: demodulator.vi) now.

But it has long periodical "noise" as shown in fig.1 .(attachement: fig1.png)

I'm thinking that the reason where such noise come from is the low-precision of USRP 2920's LO.

Is this right? First question is this. 

So, I input reference signal at 10MHz from same signal generator in order to lock USRP's LO.

But even if I input such reference signal to USRP, above mentioned noise is not improved.

In addition, while inputting the ref signal, its LED"E" on the front panel do not blink.

And while running my program, it turns on GREEN light WITHOUT reference signal.

After running my program, it blinks by changing the speed of blinkng.

So can not make sure that the reference signal is actually locking the LO.

Is this correct behavior? If not, how can I correct it?

Thank you, 

  Yuki