On 02/19/2020 12:01 PM, Alvaro Pendas via USRP-users wrote:
Hello,
I am using GNU Radio and the USRP B200. I have noticed that for the
GNU block UHD: USRP Sink, the values you pass to the block must be in
the range 0 to 1. I guess that means if you do not want to lose
resolution you must ensure that you use the full range, that is to
say, your minimum is 0 or close to 0, and your max is 1 or close to 1.
Am I correct?
On the other hand, what are the meaning of the values produce by the
block UHD: USRP Source? They must be related to the signal power, but
I am not sure about their range. Is the minimum value that block can
produce the min of the ADC output, and the max, the max of the ADC
output? With the USRP B200 the ADC resolution is 12 bits, are the min
and the max always set with the same value, or does it depend on the
USRP configuration?
I am using GNU Radio right now, but probably, just knowing how this
works with UHD would be enough to understand the rest.
Thank you for your time,
Alvaro
Gnu radio generally likes to have baesband data streams scaled into
{-1.0,+1.0} which are linearly related to instantaneous voltages at
the antenna of the hardware.
To a first approximation, a value near +1.0 or -1.0 will drive the ADC
to its maximum +/- value. But that's only an approximation, since the
signal is processed a fair amount (linearly) prior to reaching the
ADC/DAC, and with analog hardware there's no way of ensuring that
a max value wont' over-drive the analog hardware.
Power of a sinusoidal signal is proportional to the I*I + Q*Q --
remember we're dealing with *voltages* here, so ohms law applies...
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