Your "control boxes" are Modems (short for MODulator/DEModulator).
Of course, these boxes need to be aware of what kind of transmission they do. You can transmit any sufficiently band-limited signal over an RF link.
So these boxes might just be transmitting garage door opener codes, they might be transmitting analog audio that is analogly modulated as FM, they might transmit the same audio modulated as analog AM, but they might also transmit that same audio using a digital audio transmission standard.
Realistically, microwave communication links of the last 30 years can be expected to be digital, since you usually want to transmit data that is already in digital form, anyway.