Thanks a lot for your answer Derek.
2017-07-06 6:32 GMT-05:00 Derek Kozel <[email protected]>: > 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 > > I run it and, as you indicated, the values are in that range. > 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. > There's my doubt. I'm working over the Bastian's flowgraph of IEEE802.11a/g/p. Bastian put two slicers from 0 to 1 for Rx and Tx gain, the default value is 0.75. That's what i though the range of the gain was from 0 to 1, because it was normalized. In the USRP_source.cc they declare two functions: usrp_source_impl::*set_gain*(double gain, const std::string &name, size_t chan) { ... } void usrp_source_impl::*set_normalized_gain*(double norm_gain, size_t chan) { ... if (norm_gain > 1.0 || norm_gain < 0.0) { throw std::runtime_error("Normalized gain out of range, must be in [0, 1]."); } .... } If I try to put in the Gain of the block "2" then it appears: [image: Imágenes integradas 1] So, the interval is normalized (between 0 to 1), that means the flowgraph is using the second function. But maybe i have to denormalize it in dB and later get the new signal. I'm going to write you again, if I found how the mathematical relation is build. However, if you have an idea of how it could look, I would be very grateful if you let me know. Thanks for your time. Best regards, Cristian > > 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 < > [email protected]> 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 >> [email protected] >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >
_______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
