On 03/25/2011 08:01 PM, Yan Nie wrote:
Dear all,
I'm wondering how to correspond the amplitude set in software to the voltage of
the signal. I did some test, which demonstrate that setting the amplitude to
32767 and the GPA gain to 20dB could reach full scale 2V p-p. I'm confused
about the amplitude setting in software, if 32767(which is 2^15-1) reaches the
full scale, which means the amplitude is 16-bit data, but the ADCs are only
14-bit. How could the amplitude setting correspond to the voltage of the
signal? What about the receiver side?
A simple question: if using usrp_source_c to receive complex signal by LFRX,
does both of RX_B and RX_A ports should connect to antenna? This is for double
checking if my system setting is correctly. Really appreciate any of your help!
Wish you a great weekend!
Yan
The numerical view within the flow-graph corresponds only very-roughly
to what happens in the analog world on the other side of
the ADC/DAC.
In the UHD universe, using complex-float representation, everything is
scaled to +/-1.0 by UHD so that flow-graphs can be reasonably
"generic", and UHD takes care of scaling for the appropriate hardware.
For both transmit and receive, if you want a high-precision correlation
between what the flow-graphs world-view is and the outside world,
you'll have to *take measurements*, and calibrate appropriately.
You calibration is going to be slightly different from daughtercard to
daughtercard--just a fact of life in the analog world. Total gain
can vary by a dB or three, even for identical settings in the digital world.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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