Re: [Discuss-gnuradio] Questions on DDC output

[Firas A.]

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 Lin wrote:
> 
> 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 show 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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