Now that we have the NCO mode working nicely using the on-board VCXO, PLL and clock distribution, we wish to substitute an external CLK to the CLKIN J17 of the DAC38J84EVM. We obviously need to make some changes on the GUI Quick Start page, it’s just not obvious what needs to be changed other than “EVM Clocking Mode”. Starting from the configuration file that produces 100 MHz through the NCO, we have been able to adjust the output frequency to Fs/4 and make some meaningful phase noise measurements but have concluded we are mostly analyzing the PLL in the clock chip. We wish to supply an external low-noise carrier at the highest frequency possible and reevaluate phase noise. The Quick Start does not get updated from the config file, so it’s hard to guess what values we need in Step 2. Possibly, some of these settings don’t even need to be set to anything in particular, it’s just not obvious to me. The assumption is, once we have this working externally, we should be able to dial the frequency around at will and the NCO will just continue to clock the external signal source as we dial it around.