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AD9361 Filter Wizard Fcutoff

Question asked by Carsten on Sep 30, 2016
Latest reply on Oct 5, 2016 by timh

Hi,

I have some problems with the filter wizard 16.1.2.

I made a RX filter for Fpass = 20.48 MHz and Fstop = 25.6 MHz.After putting it to noos and sweeping a carrier over the full spectrum, the gain is falling from DC to +/-Fpass of about 3dB.

By increasing the RFbw manually by using ad9361_set_rx_rf_bandwidth the gain seems to get better at some point and overshootinga a tiny bit later on.

 

I noticed the Fcutoff(Analog) and the RF field acting weird. Fcutoff should be set to 20.48*1.4=28.672 but is set to 27.1117 and the RF is should be set to 20.48*2.5=51.2 but is set to 38.731. If i put the cursor in the Fcutoff field and hitting enter the values are decreasing even more.

Here are my RX-Settings:

          int_FIR: 1
             Fpass: 20480000
             Fstop: 25600000
             Apass: 0.0100
             Astop: 80
          FIRdBmin: 80
             Rdata: 61440000
              Type: 'Lowpass'
              wnom: 28672000
              RFbw: 51200000
          PLL_mult: 2
          PLL_rate: 983040000
              RxTx: 'Rx'
           DAC_div: 1
               HB3: 2
               HB2: 2
               HB1: 1
               FIR: 2
              phEQ: 0
    converter_rate: 491520000

(from the ad9361_settings.mat), wnom and RFbw get overwritten by GUI.

and the output for No-OS:

{ //RXFIR
        3, // rx
        -6, // rx_gain
        2, // rx_dec
        {-87,-8,157,276,160,-148,-317,-84,351,444,-44,-618,-513,324,954,458,-796,-1309,-180,1503,1607,-455,-2503,-1744,1681,3992,1593,-4182,-6964,-1111,11964,23685,25354,15873,2642,-5185,-4436,602,3525,1987,-1263,-2419,-749,1352,1558,53,-1193,-898,297,921,427,-415,-630,-128,394,380,-26,-298,-178,124,275,184,25,-78,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}, // rx_coef[128]
        64, // rx_coef_size
        {983040000,491520000,245760000,122880000,122880000,61440000}, // rx_path_clks[6]
        38731004 // rx_bandwidth
    }

So what is going wrong?

Why aren't the values for RFbw matching?

btw: what is the resolution of the RFBW setting, the steps actually applied seem to be large.

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