There are "I OUTPUT" and "Q OUTPUT" at the rear panel of the E4438C. I wonder if anyone had hacked E4438C to function as an ARB (arbitrary waveform generator) after downloading the waveform data into the memory, and take the baseband output at the rear panel "I OUTPUT" or "Q OUTPUT".
There is a "LF" output on the front panel, but the maximum frequency is 100kHz and the waveforms are standard waveforms set internally in E4438C. That is not what I want.
I don’t really understand what you mean by hacking the E4438C. If you want the E4438C to function as an ARB, you will need to purchase the Internal baseband generator option. The option would be either a a 601 or 602. It comes with digital bus capability and can be used to produce arbitrary and real-time I/Q waveforms.