I have an RX instability issue working with the AD9361.
I'm using FMCOMMS3 and FMCOMMS5 on a KC705 board with the latest no-os drivers and the ZC706 with the original SD card from Analog Devices.
The AD9361 Rx input is connected to a Vector Signal Generator outputting a 2-8MHz BW pulsed signal @ 1400MHz.
The AD9361 Rx configuration is (See attached AD9361_Configuration.jpg) :
- 1400MHz LO
- 50MHz BW
- 60 MSPS
- manual gain @ 20-30Db
- No FIR
- No IF frquency - Working in baseband
On normal operation, when the VSG RF and AD9361 RF carriers are synchronized, i'm seeing random, strong amplitude variation, mainly in the Q channel.(See time-domain image attached AD9361_Normal.jpg)
When the VSG RF and AD9361 RF carrier frequencies are slightly shifted (even less than 1Khz) then the signal looks much better.(See time-domain image attached AD9361_Small_Frequency_Offset.jpg)
While playing with the configurations i saw that turning off the Rx Quadrature Tracking gives much better results although there seems to be a small ripple on the signal envelope but this seems something i might be able to live with. (See time-domain image attached AD9361_Quad_Tracking_Disabled.jpg)
I would like to know if there is some problem working in baseband or is there some calibration i am missing and why is the RX quadrature tracking causing a distorted signal.
Thanks in advance for any help offered,