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AD9361 Rx noise floor

Question asked by jfp on Mar 7, 2016
Latest reply on Mar 10, 2016 by jfp

Hi there,

 

We are working with FMCOMMS3 board and no_OS project. We configure the ad9361 chip successfully using the SPI bus.

We only use the module “axi_ad9361_dev_if” (from the verilog project) to manage the transmitted and received data. We think that the other verilog modules are useless for our purpose.

 

One of our first tests is to analyze what we receive in absence of incoming signal (connecting a termination to the receiver antenna). The test was performed under the following conditions:

 

  • AGC disabled.
  • In the receiver chain we enable HB1, HB2 and HB3 filter. Besides we enable the FIR filter with the following coefficients with the aim to eliminate the shape noise without attenuate our band of interest.

AD9361_RXFIRConfig rx_fir_config = {

3, // rx;

0, // rx_gain;

1, // rx_dec;

{154, 206, -370, -547, 147, -105, -406, 426,

-144, -492, 786, -383, -623, 1386, -999, -744,

2769, -3074, -813, 18445, 18445, -813, -3074, 2769,

-744, -999, 1386, -623, -383, 786, -492, -144,

426, -406, -105, 147, -547, -370, 206, 154,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0,

0, 0, 0, 0, 0, 0, 0, 0}, // rx_coef[128];

48 // rx_coef_size

};


Using ChipScope we capture the signal received in our system. We appreciate a small noise. We would be pleased to know the reason and the origin of this noise. Are we doing something wrong? Could you tell us what is the sensitivity of the receiver?

 

We attach images of this noise in the time and frequency domains.

 

  noise2.png

noise1.png

Many thanks,

 

Juan.

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