Are you connecting all coax shields to ground? You shouldn't have noise.
You don't really need Rt if the coax is that short. In fact, you shouldn't really even need coax. Three inches is too short to cause reflections at video frequencies. You do need all grounds connected together (source, amplifier and destination). It is not clear in the schematic from Analog Devices that the coax shields must all be grounded.
Keep in mind that there may already be a 75 ohm termination somewhere.
You don't really need Rt if the coax is that short. In fact, you shouldn't really even need coax. Three inches is too short to cause reflections at video frequencies. You do need all grounds connected together (source, amplifier and destination). It is not clear in the schematic from Analog Devices that the coax shields must all be grounded.
Keep in mind that there may already be a 75 ohm termination somewhere.