Re: [Discuss-gnuradio] Question about 16 bit signed integer samples

[Eric Blossom]

On Fri, Mar 12, 2010 at 11:17:13AM +0100, Sergio Benco wrote:
> 
> I'm interested in extracting samples from USRP to perform some spectrum
> analysis on them. I use an USRP and a XCVR2450 to receive signals in the
> ISM 2.4GHz band. My setup in GRC is a USRP (decim 64, gain 0dB, baseband
> 2.405GHz) connected to a file sink. This file is then processed by
> read_complex_binary.m located in the directory .../gnuradio-core/utils/.
> Its output, for a sampling rate of 1MS/s, gives (I printed out only a
> small part):
> 
>      -18 -    19i
>      -22 -    12i
>       -2 -     8i
>      -23 -    31i
>       21 +    62i
>      -62 -   231i
>       76 +   510i
>     -128 -  1023i
>      240 +  1925i
>     -571 -  3749i
>     3643 + 10423i
>    14675 - 14352i
>    21379 +  3772i
>    -1807 +  4089i
>      851 -  2080i
>     -483 +  1112i
>      251 -   553i
>     -135 +   256i
>       54 -    96i
>      -24 +    13i
>       -3 -    12i
>       -8 -     1i
>       -8 -     1i
> 
> Now I would to know how the 12 bit samples from ADC are mapped in 16 bit
> signed integers. Since now I know that the samples (12 bit, 4096 levels)
> come into the USB after a mapping to USB's 16 bit signed integers with 4
> bits zeroed. I would understand better the process of sampling in the
> USRP from the analog signal, to 12 bit samples (signed? so 2^11 levels =
> 2048), to 16 bit signed integers (2^15 = 32768) as seems to be appened
> from my printout. How could I correlate the signal on antenna with these
> 16 bit samples?
> 
> BR, 
> Sergio Benco

Please read the USRP FAQ.

Eric