Frequency Shift Keying (FSK)

For signaling Z (logical 1) a high frequency is used (700Hz, 3150Hz). For signaling A (logical 0) a lower frequency is used (500Hz, 2250Hz). Both frequencies have the same amplitude.

In frequency domain ...

For sending a character the transmitter switches between the corresponding frequency with the giver baud rate.

For timing see: Baudot-Murray-Code