You don't need to take the FFT to get the power. See my attached example (in GR 3.7). Just take the output from the USRP, complex_to_mag_squared, integration with decimation to 1 Hz, 10*log10() + k, and probe at 1 Hz rate.
I'm using an N210 + WBX with gain=15 dB. That gives me a calibration factor of k=-34.8 dB. I can vary power of my signal generator from -50 dBm to -10 dBm with less that 0.1 dB error in the calculated power. https://dl.dropboxusercontent.com/u/49570443/power_calc.grc https://dl.dropboxusercontent.com/u/49570443/power_calc.grc.png Thanks, Lou KD4HSO <http://gnuradio.4.n7.nabble.com/file/n49981/power_calc.png> Gayathri Ramasubramanian wrote > Hi > > Thank you for your note. > > I am trying to get the power of received signal using the blocks you had > suggested previously. > I have attached a flow graph snapshot ('uhd_fft_DK.grc.png"). > > I am using the UHD:USRP Source to receive the signal which in turn sends > the signal in the foll path > "complex to Mag^2" block --> "integrate and decimate" block --> "10 log > +k" block---> "signal probe" block. > > However there are errors mainly referring to the in-compatible I/O sizes > of > source (complex to Mag ^2 block) and sink (Integrate and Decimate block). > > The I/O size of "Complex_Mag^2" block is said to be 4096, while the I/p > size of i"ntegrate and decimate" block is 4. ==> error as not compatible. > Should I change the Vector length? I am not quite sure? > The error propagates to other blocks if I change anything. > > Kindly help solve this. > > I have also attached another flowgraph (flowgraph screenshot.png) which > works but it doesn't have the "integrate and Decimate" block or the > Log10+K > block but it works and receives the signal (developed by someone else > previously in our lab). Now since the "Log10+K" block is missing, does it > mean the output is given in mwatts instead of dBm? > I cant seem to use this version on as the "probe_signal_vector" block does > not seem to be supported in GRC 3.6.4.1 which is the version in my system. > > I tried using simple probe_signal block instead but again faced the I/o > size incompatibility error? Is there a work around for this "probe signal > vector" block? > > Also could you explain briefly how to approach and solve there I/o size > errors. > > Look forward to your response > > Thanks > Gayathri -- View this message in context: http://gnuradio.4.n7.nabble.com/GR-USRP-and-GPIB-measurements-tp49727p49981.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
