ADF4371 20dB Phase Noise hit at 100Hz Foffset

Hi ADI,

I have an eval for the ADF4371 and I'm using an HMC1031 eval to lock the 100MHz ref to a precision 10MHz OCXO.  I am generating an 18GHz LO.  As seen here:

The problem here is measured PN at 100Hz offset.  With the on-board crystal reference PN @ 100Hz = -87dBc/Hz.  With HMC1031 PN @ 100Hz = -67dBc/Hz.

Notable design parameters:

- HMC1031 Loop BW set to 10Hz as outlined in the spec sheet page 12.  www.analog.com/.../hmc1031.pdf

- 100MHz VCXO, CVHD-950, CMOS output

- The measure slew rate from the HMC1031/CVHD-950 better than on board 100MHz reference.

Thanks in advance!

Chris



Adding part number to title for searching purposes
[edited by: aandrews at 9:32 AM (GMT -4) on 12 Oct 2020]