Hello Christian, The RX gain value controls the analog gain of the USRP's receiver. If you run uhd_usrp_probe on the command line you will see lines such as the following which show the gain range and step size:
| | | RX Dboard: A | | | ID: TwinRX v1.0 (0x0091) | | | _____________________________________________________ | | | / | | | | RX Frontend: 0 | | | | Name: TwinRX RX0 | | | | Antennas: RX1, RX2 | | | | Sensors: lo_locked | | | | Freq range: 10.000 to 6000.000 MHz | | | | Gain range all: 0.0 to 95.0 step 1.0 dB For every dB of gain you add at the frontend you should see a 1 dB increase in signal power amplitude. I recommend using uhd_fft or the USRP source, Frequency Sink, and a Range widget controlling RX gain to look directly at the signal. This should give you an intuitive sense of how RX gain affects your signal amplitude. >From your table it looks like you are trying to change the RX gain in steps smaller than the USRP supports. This document looks like a quick intro to power and voltage changes with dB. https://neurophysics.ucsd.edu/courses/physics_120/A%20Practical%20Guide%20to%20Decibels.pdf On Wed, Jul 5, 2017 at 10:24 PM, Cristian Rodríguez < cristian.rodriguez...@gmail.com> wrote: > Hi all. > > I'm trying to understand how Rx gain, the paremeter that is set in the > USRP Source block, affects the input signal. I would like to have an > equation for that. > > I'm doing the next experiment: > > - I take the input signal from the USRP Source block to a MAG^2 block. > - From MAG^2 block to a moving average with a window of 50K. > - My sample rate is 10M that means that my moving average is > calculated over 5ms. > - I'm sending a signal from a transmitter each 5ms. > - Finally I capture the value of the moving average, which is always > around an average value. > > Now, I change Rx gain and it is what i get: > > [image: Imágenes integradas 1] > > The value of the output of the moving average is changing very strange. I > was trying to write an equation for that, but i wasn't able, i used Rx gain > in dB, in dBm as a constant, but i wasn't able to build a relation. In an > equation i'm doing as follow: > > [image: Imágenes integradas 2] > > Then I think that if I include Gtx, my equation results in: > > [image: Imágenes integradas 3] > > But that doesn't make sense with the data that I get. > > > I would really greatful if someone can explain where is my mistake. > > > Thanks in advance. > > > Best regards, > > > Cristian > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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