Hello all, Myself Jahnavendra, I am working with the USRP1 and i tried some tutorials using the USRP (FM Receiver also). My next level is to test the USRP with signal generator and i did that recently. Following are the input parameters from signal generator: 1. Frequency =70 MHz 2. Input power = -39 dBm I changed the gain value in "USRP source" block from -110dBm to +110dBm. While testing the USRP with signal generator i got different output values. Those values are attached using Notepad. My issues are, ----> Why the power is unchanged between -110 dBm to 0 dBm of gain in "USRP source" block? ----> How to take the FFT o/p power. ----> What is the role played by this gain in the USRP source block. Please find the attachments sir. Regards, Jahnavendra.

Hello Jahnavendra Mattipa: 1. The gain value is not in dBm, it is in dB. dBm is "decibel-milliwatt" - implies that the value is a power level, and is in a known unit (mW, not W or something else). Neither is true in this case. (Yes, the gain value has relationships with the power estimates calculated from the ADC readings, but these are still two different things and must not be confused). 2. Allowable gain values depend on the daugtherboard that is installed on your USRP (GNU Radio may *not* warn you even when you are out of that boundary). Check UHD manuals. This is usually somewhere around 0 - 30 dB. That explains your first issue. 3. Data being outputted from the "WX FFT Sink" *is* the power level (it is called "FFT Sink", but it is not outputting pure FFT results). Power level, in an arbitrary scale. You *cannot* get dBm readings from USRPs unless you calibrate the results, if that is what you wanted. (Your issue #2 is unclear to me, but I guess that is what you asked?) If you want to get the power estimates (in an arbitrary scale) and to save them into a file or pass them to a next DSP block, you can use the "Log Power FFT" block instead of the "WX FFT Sink" block. 4. The "Gain" knob configures the gain level of the amplifiers (or attenuation level of attenuators) on the daughterboard of your USRP to achieve the target gain. These amplifiers amplify your signals, so higher the gain knob is, higher the ADC readings are. Only if the ADCs are not overloaded, though. Your input signal is a bit strong, so the ADC is probably operating in an nonlinear way in your case. Please read the Ettus Knowledge Base and UHD manuals, not just GNU Radio tutorials. These questions are better addressed by those documents. Regards, Kyeong Su Shin On Fri, May 26, 2017 at 3:08 AM, Jahnavendra Mattipa via USRP-users < usrp-users@lists.ettus.com> wrote: > > Hello all, > Myself Jahnavendra, I am working with the USRP1 and i tried some > tutorials using the USRP (FM Receiver also). My next level is to test the > USRP with signal generator and i did that recently. > Following are the input parameters from signal generator: > 1. Frequency =70 MHz > 2. Input power = -39 dBm > I changed the gain value in "USRP source" block from -110dBm to +110dBm. > While testing the USRP with signal generator i got different output > values. Those values are attached using Notepad. > > My issues are, > ----> Why the power is unchanged between -110 dBm to 0 dBm of gain in > "USRP source" block? > ----> How to take the FFT o/p power. > ----> What is the role played by this gain in the USRP source block. > > Please find the attachments sir. > > Regards, > Jahnavendra. > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >