Marcus, First of all thank you for your reply! I have some questions about your very much appreciated explanations: After using the complex-to-mag-squared block, should I consider the coefficients as being in W or mW (should I use 10*log10 or 30 + 10*log10 to get the power value in dBm)? What is the function of the single-pole-iir_filter? What does it actualy do? I'm asking this so I will know how to calculate its parameters. Does it give the frequency bin based signal band, a more rounded appearance? Again thank you for your help! I hope other people will also find this useful.
Vlad. =================================================================== Marcus D. Leech wrote: > > On 11/28/2010 08:38 AM, Vladutzzz wrote: >> Dear all, >> I would like to receive as many suggestions as possible on how to >> accurately >> measure bandpower with a USRP2 + WBX setup. >> I know I should use a block that does the square magnitude (FFT squared) >> and >> sum the resulting coefficients but after this I don't really know what >> the >> correct procedure is. I would like to have the value in dBm and I know >> I'm >> suppose to use 30 dBm + 10log10, but the resulting value is not the >> correct >> one. >> Please help me by offering your insight on this matter. >> Thanks! >> >> Vlad. >> > The basic flow for power measurement is: > > source-->bandpass_filter->complex-to-mag-squared--> > > single-pole-iir_filter-->calib_multiplier-->calib_offset-->log10*10 > > > You'll need to determine your calibration constants by experiment, and > you'd need to determine > what those should be for any given > bandwidth/center-frequency/gain-setting. > > You can't simply apply a fixed formula--there are too many uncertainties > in the analog realm > to make precision power measurement work without caibration > experiments. The power > seen by your detector (complex-to-mag-squared+filter) will be > proportional to: > > GAIN*(system-noise+signal-power) > > There's substantial uncertainty in the *precise* value of GAIN, due to > *inevitable, expected* > part-to-part variability. If you, for example, command the GAIN on > your daughtercard to > 65dB gain, the actual gain may vary by up to about 2dB, and such > uncertainties are > generally frequency dependent. RF amplifiers usually have somewhat > more gain at their > "bottom end" than at the "top end" of their frequency range. Further, > you don't know > how much system-noise there is, at least, not precisely, which means > that for measuring > very small signals, the total-power seen by the detector may be > dominated by system-noise. > > So, you have calibrate, through experiment. If you're trying to make > precision power measurements, > you're going to have to calibrate for each variation in your system > setup (gain settings, > frequency settings, bandwidth settings). > > > -- > Principal Investigator > Shirleys Bay Radio Astronomy Consortium > http://www.sbrac.org > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > -- View this message in context: http://old.nabble.com/Bandpower-measurment-USRP2-tp30323488p30326643.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
