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REceived I/Q with Q almost 10 times lower than I.

Question asked by Chuppa on Oct 11, 2017
Latest reply on Dec 4, 2017 by travisfcollins


I am designing qpsk modem in simulink and trying to port on picozed SDR.and we are using ad9361 in some of our SDR for indian military There is a training sequence of 416 I/Q symbols alternate (0.7+0.7i) and (-0.7-0.7i)   these are generated at 520.841e3/4 ksps and sent to RRC filter with 4 interpolation factor so final output at 520.841e3 is captured and sent to board using matlab script.

the sequence has gone through ad9361tx and rx on same board and collected samples in simulink. ad9361 is configured through sdr receiver for fcomm and ad9361.

In the received samples I is of order 10e-2 and q is of order 10e-3 and instead of alternate Q is always negative with very low value.

I have attached the pictures which is in simulation and with captured samples.

It is not even like I/Q imbalance i have tried enabling quadrature DC tracking and all such things.

AD9361 filter settings is changed through matlab in that too fs is given as 0.520841Mhz and Fc 0.171MHz and Fstop is 0.21Mhz. i didnt use any phase equalisation or any advanced settings.

Kindly help me out sir and tell me any data is required.