Hello,
I wish to use USRPX310 with UBX-160 daughterboard as a calibrated spectrum analyzer to show the received signal power in units of [dBm] and [dBFS] for my setup.
I've read discussion and the GNURadio FAQ before so I know I must calibrate my setup because the values in GNURadio don't mean a thing.
So I wanted to ask if this procedure seems to make sense for you. I will be glad to receive any suggestions.
I'm gonna connect my signal generator to spectrum analyzer to measure the cable loss.
After that, gonna connect it to the USRP to measure the power[dB] in order to understand what is the power[dBm] in GNURadio.
Is this table correct to calibrate and calculate the Power[dBm] on GNURadio in FFT?
| Signal generator Power[dBm] | Power [dBm] on spectrum anlayzer | Power[dB] on GNURadio in FFT | Power[dBm] on GNURadio in FFT |
| -60 | -61 | -66 | -61 |
| -65 | -66 | -71 | -66 |
| -70 | -71 | -76 | -71 |
| -75 | -76 | -81 | -76 |
| -80 | -81 | -86 | -81 |
| -85 | -86 | -91 | -86 |
| -90 | -91 | -96 | -91 |
Procedure for wideband signal (not CW)
Right now the power[dB] must be calculated with the occupied FFT bins, let's assume this is the signal and the NFFT=128, so we can see that the signal occupies only 2/10 grids in the FFT so:
Power_of_signal[dB] = Peak_power[dB]+ 10*log(FFT_bins_with_signal) = (-15dB) + 10*log10((2/10)*(128)) = (-15dB) + (14) = (-1dB)
Convert to dBFS for the USRP X310
How do you propose to do it?
The ADC of X310 has 14 bits. so the MSB values are 2^13 = + - 8192 (signed values).
Power[dBFS] = 20*log10(voltage_value_measured/8192)
Some questions:
- Does the gnuradio amplitude axis in QT GUI TIME DOMAIN are always float-point values in the range {-1.0,+1.0} for a received signal from USRP?
- If the answer to 1 is yes, then if I see amplitude = 0.5 , does it mean 20*log10(0.5)=(-6dBFS) ? is that correct?
- I know that the maximum input power for the UBX is (-15 dBm), but what does it mean that (-15dBm) input power is 0[dBFS]?
- Has anyone had experience with RX power calibration of USRPX310 with UBX-160?
If I understand correctly, it is supporting the power API:
Thanks
Dor