when i run the Matlab Simulink example "ad9361_LTE.slx" form LTE Transmitter and Receiver Example [Analog Devices Wiki] with loopback cable between Tx1 and Rx1, i get the result shown in the appendix. The phase of the constellation-points is ok but the amplitudes are very bad what gives an EVM around 8%.
The text in LTE Transmitter and Receiver Example [Analog Devices Wiki] says:
"According to the experiment, when the digital Tx - digital Rx loopback is used (RF bypassed), the overall EVM is around 0.077%. When a loopback cable is used between Tx and Rx (RF included), the overall EVM is below 2%."
I can confirm the 0.077% in RF-bypassed-mode but not the 2% when RF is included. I use ZedBoard with AD_FMCOMMS3-EBZ and another SDR-Board with Xilinx Zynq and AD9361 NAMC-SDR RF interface for Software Defined Radio and get exactly the same results.
I tried slow_attack, fast_attack, manual with various gains and tracking modes enabled and disabled but still bad amplitudes. The used filter is LTE1p4_MHz.ftr from analogdevicesinc github. All DDS-tones are disabled.
Does someone have an idea how to improve the amplitudes of the symbols for a better EVM?