This is the very baises of Spread Spectrum. Each radio has a unique code that is used to control the modulation of the transmitter, which, if I understand correctly, is what spreads the frequency out. If your reciever does not have the code it can not demodulate the signal, and like wise any other transmitter can not create a signal that your reciever can recieve. Your signal just looks like a small increase in the noise to another radio. Again if I understand it correctly the transmitter sends out a sync signal, which I guess can be used to let the other radios know that the frequency is in use.

Steven