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
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