Relation between the amplitude and the voltage of the signal

GNU Radio
1

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

2

On 03/25/2011 08:01 PM, Yan N. wrote:

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 L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium