A microchannel plate is demonstrated as both an optical low-pass filter and a heterodyning modulator. The frequency response function of the microchannel plate indicates it behaves as a low-pass filter. Antialiasing with the microchannel plate is demonstrated using a two-tone amplitude modulated laser beam, with the higher tone above the cutoff frequency being successfully suppressed while the frequency within the bandwidth of the filter is passed through. Selection of different commercially available phosphors controls the filtering and frequency response characteristics of the optical filter, effectively moving the cutoff frequency. By gating the microchannel plate at different frequencies, the microchannel plate can also be used analogously to a heterodyning spectrum analyzer, supplying all of the required functions of a local oscillator, mixer, and filter.