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AD-FMCCOMMS1 always cuts sampling frequency in half?

Question asked by superco on Mar 29, 2015
Latest reply on May 8, 2015 by superco

Hello,

I am trying to transmit a wideband IQ signal with AD-FMCCOMMS1+Zedboard.

Using the reference image on AD-FMCOMMS1-EBZ User Guide [Analog Devices Wiki], and iio-oscilloscope,

the DAC sampling rate is set to 491.52 MHz, and  HB1 in 00 mode, and bypassing the HB2, HB3 filter (no interpolation).

 

The generated output was monitored by an Spectrum analyzer.

I can say that the main signal is generated as intended, but I see images at +-245.76MHz(=491.52/2) that makes the signal bandwidth limited to about 245.76MHz.

However, because the f_data = 491.52, and it's in IQ complex mode, I guess it is supposed to support the bandwidth of 393.216MHz(=0.8x 491.52MHz) (from AD-9122 datasheet, Table22, the supported bandwidth is 400MHz (=0.8x500MHz) in word mode, when f_data=500MHz).

Capture_1.PNG

Interpolating X2 option only helps to suppress the image outside 245.76MHz.

And the same thing happens when I use the 'qam16_20M.txt' waveform under iio-oscilloscope/waveforms/.

 

Any help to push these images to f_data (Hz) would be appreciated.

 

Thank you.

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