Check the type of calcuation you want, enter the signal frequency in MHz, and either jitter in ps rms or desired MER in dB. Then press the Calculate button to compute the MER or jitter. Yellow field indicates the answer (and is read only).
One of the factors impacting the MER is the jitter or phase noise of the LO or sampling clock, scaled to the frequency of the signal (will decrease 6 dB/octave when signal frequency is reduced). The figure on the top of the page illustrates the impact of phase error relative to the ideal constellation point.