keenyx1,
Nice simple question, and a reasonable one!
Absolutely any number is the simple answer, and DG has pretty well said it.
The Tx sends a coded signal, which only a receiver "bonded" to that code can respond to. I'm sure that the receiver you got with the transmitter is already bonded, if not it is very simple.
You can buy as many receivers as you like/can afford and bond them to yout Tx then the same transmitter will control all of them, but probably not at the same time
Its not a computer radio, so it doesn't remember all the cunning trim settings, throws and mixes for a particular model - this is what bunkerbarges reply refers to.
So when you change models you have to check that all the controls go in the correst direction before you launch (but you would do that anyway
)
andrew