Hello Joe,
You probably call Signal Generators to the Up and Downconverters. In this case, as Andy explains in
this forum (
Phase Locking the Up and Down Converter Modules), the modules will be locked with a non predictable phase difference which will change every time is re-tunned.
What are you trying to accomplish? Is this something related to the previous post?
Good luck,
Gerardo O.
RF SW Engineering R&D
National Instruments