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Re: [Discuss-gnuradio] Question about 16 bit signed integer samples
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] Question about 16 bit signed integer samples |
Date: |
Tue, 23 Mar 2010 14:00:14 -0700 |
User-agent: |
Mutt/1.5.20 (2009-08-17) |
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