[volt-nuts] External Freq Reference Mod for 3458A?

[Tom Knox]

Does any of the Volt-Nuts brain trust have any experience adding an external Frequency Reference on the 3458A.
There is a 20MHz reference on the A/D board but externally clocking it has affected linearity collecting data off a 10VDC reference that looks a little like a hanging bridge I have seen before between GPS and oscillator sync. Is there another clock?  Thanks for any thoughts.

Thomas Knox