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HMC363S8G eval board noise at Low Frequency

Hi,

We are using eval board for the HMC363S8G and have some noise issues at lower frequencies.  The performance is good at input frequencies above 100 MHz, but when I lower my input frequency to 30 MHz (3.75MHZ output) I start to see spurs above the noise floor at various frequencies (11.25MHz, 18.75MHZ, and 26.5MHz) these are not expected.  My fundamental is -40dB.  Input level is at 4dBm.   Further, when I decrease my input frequency to 16MHz, I see no output spectrum other than white noise.

Can you help explain what I am doing wrong?

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  • Thanks!

    I was hoping that by increasing the blocking caps that I would get some more response down below 10 MHz.  After switching all the AC couplers from 100 pf to 100 nF, I can now see normal operation at 9 MHz now (down from 50 MHz).  I do have to drive my input at +20 dBm (with a sine wave, though).  I'll double check and see if I can get a little lower frequency performance with a square wave input.  

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  • Thanks!

    I was hoping that by increasing the blocking caps that I would get some more response down below 10 MHz.  After switching all the AC couplers from 100 pf to 100 nF, I can now see normal operation at 9 MHz now (down from 50 MHz).  I do have to drive my input at +20 dBm (with a sine wave, though).  I'll double check and see if I can get a little lower frequency performance with a square wave input.  

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