A Continuous Phase Frequency Shift Keying modulator provided to receive a series of binary symbols having a predetermined repetition period, and generate a series of sinusoidal signals comprising in sequence: a first sinusoidal signal with a first frequency in response to each received binary symbol having a first binary value; and a second sinusoidal signal with a second frequency in response to a received binary symbol having a second binary value, where the lowest of the first and second frequencies is larger than or equal to a third of the symbol rate; wherein the sinusoidal signals are shortened or lengthened with respect to the binary symbol they respond to, such that each first sinusoidal signal comprises an integer number of half periods of said first frequency and each second sinusoidal signal comprises an integer number of half periods of said second frequency.