Re: [Discuss-gnuradio] USRP Input Calibration / CIC Filter Response

[Eric Blossom]

On Mon, Mar 23, 2009 at 12:58:17PM -0400, Erich Stuntebeck wrote:
> The daughterboard gain was set to the mid-point.
>
> I don't have the range of the time domain samples as I did the FFT  
> processing in real-time and discarded the raw data. The data was  
> collected using a script I wrote to link the USRP block with a custom  
> processing block that I wrote. This custom block take the FFT of the  
> incoming data and outputs the amplitude of the appropriate bin. It  
> determines the appropriate bin based on a given frequency as an input,  
> and searches a few neighboring bins in case of clock errors to select  
> the bin nearby with the maximum amplitude.
>
> I'm using the firmware without the half-band filter.
>
> The signal generator is an Agilent 33220A. I don't have a spectrum  
> analyzer, but I do have two of the 33220A's and they both perform the  
> same way so I'm guessing its not a calibration issue with the signal  
> generator.

Thanks, Erich.

Without seeing the time domain samples, I'm guessing that the gain is
too low and/or the input is too low, and that what you're seeing is
the result of only a few of the least significant bits moving in
received samples.  That is, you're not using the full dynamic range of
the signal processing pipeline.  I suggest running it again with the
Rx gain set to its maximum value.  Let us know how it turns out.

Eric