Wow, that's an antique. But if its still working, probably a great unit.
There's a manual here - http://manuals.repeater-builder.com/te-files/R&S/R&S%20CMT%2052,%2054%20Operating.pdf
Section 2.4 covers remote control. That's not an IEEE 488 (GPIB) connector, but an older model (1985?) IEC 625 connector, so it might not respond to NI-MAX. But if you see the instrument there then you should be able to send it commands. (Its not going to respond to the *IDN?\n IEEE-488.2 query, that's for sure!)
The termination char is \n from my skimming of the manual. You might try sending the "RF:POW?\n" string and seeing if you get a reply. (This is a query of the RF power.)
Once you can establish that the bus is working, and make changes to the instrument remotely the job becomes sitting down with the manual and reading all the commands required to make the measurements you want to make and how to get the data back. Looks like the instrument also has the ability to run "scripts" natively. If you have an existing collection of these I've often found a good solution for older instruments is to use PC to tell the instrument to load a setup file or run a script on the instrument, then transfer data to PC.
Should be a good challenge to get it running. Good luck!
Craig
