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FMCOMMS5 Unable to get phase coherent TX and RX signals for beamforming

Question asked by Merling on Aug 9, 2018
Latest reply on Aug 15, 2018 by Merling

Hello,

 

      I am using FMCOMMS5 and ZC702 as a signal source for transmit beamforming. However, there arises a problem in calibrating all 4 channels of FMCOMMS5 on both IIO-Oscilloscope and a real Oscilloscope.

      I followed the procedures to calibrate the FMCOMMS5 in the FMCOMMS5 plugin as

       

      1. Set all AGCs to manual mode, and the same carrier freq and sampling rate for both TX and RX.

      2. Run MCS by clicking the button in the bottom.

      3. Run calibration (there are 5 options in the pop-up toggle and their calibration results seem to be almost idential).

 

 

      After that, I check in IIO-Oscilloscope each two pairs of the 4 channels, the result is

      1. Each two channels of one single AD9361 seem to be almost coherent, especially, two channels of the first AD9361 are almost phase cohererent, while that of the second one has an observable phase offset within 20°.

      2. Each two channel of different AD9361 is not phase coherent at all even though the TX phase between them has been adjusted automatically during the calibration procedure.

 

      The results of TX signals observed by using a real dual-trace oscilloscope are almost the same, except that there is an approximate 45° phase shift between two channels of one signal AD 9361.

 

      My question is, can I get phase coherent receive signals in IIO-Oscilloscope through the calibration procedure? And more SPECIFICALLY,  can I get phase coherent transmit signals for transmit beamforming by using the calibration procedure?

 

      I wonder if I have missed something, or otherwise, please give me some suggestions in solving this problem. Thanks very much.

 

Sincerely yours

Wayne

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