[Discuss-gnuradio] Questions on DDC output

[Brook Lin]

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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