I think this should be the last question in this thread. Which input signal levels should I stick? OIP3 at the first LNA MGA-62563 is 23 dBm. Since the gain is arround 22 dB, is it ok to stay below -20dBm?
Best, Nemanja On Wed, Jul 10, 2013 at 2:33 PM, Marcus D. Leech <[email protected]> wrote: > ** > > I think that i am a little bit confused with calibration. Is there any way > to determine the gain of the circuitry in front of the ADC? Is it correct > enough to say that power level at the input of PGA in front of ADC is > just ((sampled_value*Vp-p)/2^12 ^ 2 ) / Rinputpga? > > The total gain in front of the ADC will vary from daughtercard to > daughtercard, and with frequency. > > Calculate the power inside the flow-graph, which is proportional to > AVG(I*I + Q*Q). For RMS power, there's an RMS block. > > What you need to do is use a *calibrated-in-power* signal source, and use > that to calibrate your receiving setup. > > You can't reliably backtrack from the values coming out of the USRP, > because you don't know the total gain in front of the ADC to sufficient > precision. > > > > > On Mon, Jun 3, 2013 at 5:05 PM, Marcus Leech <[email protected]> wrote: > >> I'd tune slightly-off the target frequency. The gain isn't going to >> change that rapidly across the tuned frequency range. If I were doing >> this, I'd probably calibrate every 20Mhz or so. >> >> Since neither UHD nor Gnu Radio have the concept of calibration data, >> you can store it in whatever way is appropriate for your application. It's >> a simple matter of programming... >> >> on Jun 03, 2013, *Nemanja Savic* <[email protected]> wrote: >> >> Thank you Marcus for super fast answer. Well, for the begining I would >> like to skip temperature calibration, only power level calibration >> regarding frequency. I have following doubts: >> 1. To which frequency should be tuned USRP if for example generator >> generates 400 MHz. Should it be almost the same frequency, so that >> downconverted signal falls very close to DC or something else. >> 2. What is the best advice for storing calibration data. >> >> >> On Mon, Jun 3, 2013 at 4:44 PM, Marcus Leech <[email protected]> wrote: >> >>> Indeed, the only way to do this is to use a signal generator with known >>> power levels, and precision attenuators. You'll have to repeat the process >>> over the full tuning range of the device(s) in question, since >>> effective gain will change a little with tuned frequency--that's just a >>> natural property of analog RF components. The gain will also change (a >>> little) with ambient temperature as well, so it depends on how precise you >>> want your calibrations to be. >>> >>> >>> >>> on Jun 03, 2013, *Nemanja Savic* <[email protected]> wrote: >>> >>> Hi all guys (yet again), >>> I have a question about calibrating received power level of my USRP, >>> equipped with wbx, lftx and lfrx. >>> I am not sure whether it is apropriate to discuss that here. >>> Basically I would like to be able to determine absolute power level I am >>> receiving. I suppose that basic procedure for doing this would be using >>> super precise, expensive signal generator. Then tracing signal of know >>> power to daughter board and measure power level in fft sink. And maybe also >>> doing this for complete band of daughterboard usage. If the previous is >>> correct, than I would like to ask you, how do you store calibrating data, >>> inside .h file or ...? >>> Best and thank you, >>> >>> -- >>> Nemanja Savić >>> ------------------------------ >>> >>> _______________________________________________ >>> Discuss-gnuradio mailing list >>> [email protected] >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >>> >>> >> >> >> -- >> Nemanja Savić >> >> > > > -- > Nemanja Savić > > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortiumhttp://www.sbrac.org > > -- Nemanja Savić
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