 In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.PSK and ASK, and sometimes also FSK, are often generated and detected using the principle of QAM.The I and Q signals can be combined into a complex-valued signal "I"+"jQ" (where "j" is the imaginary unit).