Hi
Thanks again fro your explanations. You were correct about the measurements I had sent in earlier. I checked with the power meter and the O/p power at 450MHz @ ampl 0.707 and TX Gain of 25 gives 11.5 dBm.
I have done the single tone and two-tone tests for USRPN210 +WBX board at 3 frequencies of 400 MHz, 900 MHz, 1800 MHz.
The settings are similar to yours :AMPL 0.707, TX gain : varied from 0 to 31.
Could you please check them and let me know if they are fine.
Also I am trying to find the RX side linearity range. For this I connected signal generator to the RX port (RF2) of the USRPN210 and viewed the received spectrum on UHD_FFT.
I have plotted the readings that I got.
I could see that there is a difference of around 35 dBm between the reading on UHD_FFT and that on spectrum Analyser when the same input from signal geenrator was given to both (using a power splitter ) @ 400 MHz.
This changed to ~ 31 dBm at 900 MHz and ~ 23 dBm at 1.8 GHz.
Could you kindly clarify the below points regd this:
1) So it is good to assume 35 dBm as a calibration factor @ 400 MHz for the USRPN210 +WBX device. i.e in case we use USRPN210 +WBX device test as Receiver for testing and use UHD_FFT to plot the spectrum and take the reading of amplitude in dB and get a value of 25 dB , would it to fine to say that 25 - 35 = -10 dBm is the actual power received by USRP to an extent ( not only on the RX port).
So can we use the difference to be the calibration factor in the linear range?
says that "
When the FFT(default) view is used, the x-scale is the frequency, and the y-scale is amplitude.The y-scale shows the amplitudewith “counts,” and the values do not typically correlate to a specific, absolute power input. The amplitude read on the display is useful for approximate comparisons. The level for a given input amplitude will vary a few dB across frequency and from unit to unit. Also, receiver daughterboards provide various levels of amplification in their analog chains,which will affect the amplitude result in the FFT".
Could you clarify what type of processing is done on the received signal from the point of reception till the display on UHD_FFT briefly in terms of scaling/ normalization.
The basic idea is to find a relation between the amplitude value shown on UHD_FTT plot and basic power scale in dBm.( a factor to be summed/subtracted or multiplied or divided from UHD_fft reading to get real power value in dBm)
3) On further increase of input power in steps of 1 dBm or 0.1 dBm, there was a 1 dB drop of power. We assumed this was the point of 1 dB Compression for the receiver side of USRPN210. Is this understanding correct? This comes around -8 dBm @ 400 MHz, -4 dBm @ 900 MHz and ~ +2 dBm @ 1.8 GHz.
4) I have also tried two tone test on the USRPN210 +WBX device. The plots shown under Q4. The IIP3 point comes ~ 4 dBm when the factor of 35 is subtracted from the values got from UHD_FFT and is ~ 25 dB on IIP3 and 50 dBm on OIP3 ( which was told to me by my advisor as not the normal values to expect) . You said you plan to do the one tone and two tone test for RX side for B200. Do you find any similarity in results. Kindly let me know if I seem to be going wrong any where.
Kindly Clarify the above points.
Plots for the Questions.docx