Heterodyne Filters

• Use heterodyning to implement a sweepable filter using a fixed lowpass filter and heterodyning

• Heterodyning is multiplication by a complex sinusoid $e^{-j\omega_c t}$ tuned to the ``sweep frequency'' $\omega_c$

• The fixed filter's bandwidth is a bandwidth control

• Requires analytic input signal (i.e., first filter out negative frequencies)