Questions on DDC output

Hi All,

I found one of replies sent by Eric said that:

What are the units of the Y axis of usrp_oscope?

They are the output of the digital down converter.
They are not calibrated to any particular voltage level.
The levels depend on the gain setting too.

My first question now is whether the red and blue lines on the oscope
are
the numbers which are the 12-bit output of the ADC multiply the
sine/cosine
@ IF? Eric said that the levels depend on the gain setting too. If the
gain
is 0, do these shows the actual signal receving by the USRP in time
domain?
So the Y-axis should be mV when gain is 0, right? However, I don’t think
the
gain and the output are linear. How does the gain effect the output of
the
DDC?

My second question is when gain is 0, usrp_fft.py shows the actual
signal in
frequency domain, and Y-axis are in mdB. Am I right? What is the 0dB in
fft?
Is it exact 0 or some reference number?

Thanks,
Brook

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Hi,

Checkout the USRP measurement pointed by :

http://www.nabble.com/USRP-Dynamic-Range-and-8-Bit-Problem-to14471573.html#a14484747

May be it will answer some of your questions. Keep in your mind that
USRP is
not a measurement device. It is an SDR peripheral device. If you want to
use
it as a measurement device, you should use a calibration method to
modify
its output to fit into your requirements.

Regards,

Firas

Brook L. wrote:

fft? Is it exact 0 or some reference number?

Thanks,
Brook


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