A/D Output

GNU Radio
1

Hello,

I am using gnuradio and a usrp2 to capture samples (shorts) to a file,
that is 16 bit I and 16 bit Q.
I looked at this data in matlab and noticed that in many instances the
samples exceed 13 and 14 bits
for both positive and negative numbers (ie -12567 or +12989).

I was under the impression that a 14 bit a/d meant 13 bits plus a sign
bit so max 8191, min -8191.

Should I expect this behavior, am I interpreting something incorrectly.
If this is expected
can someone please explain. I though the rx_gain was applied before the
a/d so the max
output would be be 13 bits plus a sign bit.

Thank you,
Sharif

2

On 09/30/2010 02:38 PM, Sharif S. wrote:

Should I expect this behavior, am I interpreting something incorrectly.
If this is expected
can someone please explain. I though the rx_gain was applied before the
a/d so the max
output would be be 13 bits plus a sign bit.

You are seeing the effect of the digital down conversion in the FPGA,
which includes scaling, and shifting, and filtering.

-Josh