sentences:  In designing a system, it is important to pick selective calling tones that do not conflict with remote control tones in use.Analog voting systems usually utilize either 2,175 Hz or 1,950 Hz as an indication a receiver is squelched or idle.In the case of 2,175 Hz, the steady tone leaking from a receiver phone line, or from the output of the voting comparator, may cause the transmitter to lock on.