Spikes in b210 received data

Hi all
I am trying to capture a cosine at 300KHz sent from a vector signal
generator(VSG) using USRP B210. VSG is connected to USRP using SMA
cable.
signal level at the input of B210 is -30dBm.

For this, I have made a simple flowgraph in GRC which is attached. Clock
reference is external and is provided from the VSG. Sampling rate is 5M,
center frequency is 100e6.

On observing the received samples, there is a periodic " ramp " on the
received sample. Attaching the plot. I do not observe this effect while
using N210. Also I do not observe this if I use the internal clock.

Thank you

Hi Arjun,

On Fri, Mar 20, 2015 at 11:15 PM, Arjun N. via USRP-users
[email protected] wrote:

On observing the received samples, there is a periodic " ramp " on the
received sample. Attaching the plot. I do not observe this effect while
using N210. Also I do not observe this if I use the internal clock.

Can you reduce the level on the VSG by a few dB and see if that
changes the behavior?

And is the ramp effect consistently tied to the use of the external
reference? or is the relationship intermittent?

-TT

Hi Tom,
I have tried reducing the signal level. The signal level at the input is
now -40dBm. Still there is this ramp behaviour.

I also get this when I use the B210 in loopback mode (with a 30dB
atttenuator in the loop). Also I have observed that
the lower the master clock rate that I set, the less frequent the ramps.

Thank you,

Arjun N.

On Tue, Mar 24, 2015 at 11:07 PM, Arjun N. [email protected]
wrote:

Thank you, Tom
That fixes the problem.

Great. Thanks for testing.

Upcoming UHD and gr-uhd changes will expose more of the AD9361
functionality, which will allow user control of calibration and
filters without having to patch UHD. We’re also looking into better
tuning of the calibration tracking to avoid such signal oddities.

-TT

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