Wow, thank you for such a detailed and thorough answer!
The specific oscillator I am using is a Connor-Winfield TVB524-080.0M; it has reasonably good specs but as you suspected, it is not intended to drive 50 ohm loads. I was going to add some series resistance to try and match the cabling and primary impedance of the transformer on the EVM. Do you have any specific recommendations there?
The specific transformer seems to have 75 ohm DC resistance on both primary and secondary, but I see on the schematic that the secondary of the transformer is terminating differentially to 50 ohms. The cabling is also going to be 50 ohms as you suspected.
