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AD9361 56MHz RX bandwidth

Question asked by ciro.improta on Jun 10, 2014
Latest reply on Jun 29, 2017 by ACozma

Hi all

 

I’m developing an application requiring 56MHz RX instantaneous bandwidth using Xilinx ZC706 Evaluation Kit and Analog Devices AD-FMCOMMS3.


By means of AD9361_Wizard_Filter I designed the RX chain as follows

wizard - design 56MHz.png

 

and exported the FIR coefficients in .trf file attached.

 

 

To configure AD9361 i’m using IIO-Oscilloscope (the latest version downloaded from GitHub).

 

The RX is equipped with 50Ohm terminal resistance and AD9361 is set as reported in the figure below

Screenshot_1.png

in particular the RX gain is set to 71dB.

 

Running IIO-Oscilloscope i get the following spectrum FLAT in the passband

 

Screenshot_2.png

 

Setting the RX gain to 0dB i get this spectrum:

 

Screenshot_3.png

 

is correct that the noise floor is NOT flat?

I expected a 56MHz wide flat noise floor: am i wrong? Do i miss anything setting AD9361 ?

Note: i had to select the desired halfband filter (HB2 and HB1) by tab Debug because selecting "Enable RX FIR Filter" in tab FMCOMMS2/3/4 (the design made by wizard is for RX chain only) enables HB3 and HB2 and bypass HB1 instead.

 

Thanks in advance

 

Ciro

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