However, the way I see it, this represents a problem in the receiving part.
Let me put it this way: the max output of the ADC is 1, and that
corresponds with the max input. That max input would represent the case
when you receive a high power signal and you set your drive amplifier next
to its max.
So, If you are receiving a low power QPSK signal, with your gain set to 30
dB, the output of your ADC would use a really small part of the range
(let's say from -0.05 to 0.05). However, if your digital levels go from -1
to 1 and are represented with 12 bits, using such a small part of the range
would make the quantization error a problem.
El mié., 19 feb. 2020 a las 20:04, Marcus D Leech (<patchvonbr...@gmail.com>)
escribió:
> Indeed. You’d have to use an external calibration source at several places
> over your parameter space (frequency gain sample rate)
>
> Sent from my iPhone
>
> On Feb 19, 2020, at 1:54 PM, Alvaro Pendas <alvarop...@gmail.com> wrote:
>
>
> Marcus thank your for your answer,
>
> First of all, you are right, the range is -1 to 1 (instead of 0 to 1 as I
> said before). So, for example, in the receiving part, the values you get
> out of the UHD Source have a linear relationship with the voltage of the
> analog signal, but I understand there is no easy way to calculate that
> level with the only information of the GNU Radio samples. Is that correct?
>
> El mié., 19 feb. 2020 a las 19:22, Marcus D. Leech via USRP-users (<
> usrp-users@lists.ettus.com>) escribió:
>
>> 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...
>>
>>
>>
>>
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users@lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>
>
_______________________________________________
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
