AnsweredAssumed Answered

Rx Quadrature Tracking

Question asked by GiladKR on Aug 5, 2015
Latest reply on Jan 6, 2016 by tlili

Hello,

 

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

AD9361_Configuration.jpg

 

 

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)

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)

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)

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,

Gilad

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