New type of time-varying octave filter

Double quadrature-modulation realisations of lowpass and highpass filters were described recently by Saraga. Extensions to these methods lead to the design of an octave filter using one carrier oscillator rather than the two needed for an equivalent filter designed by the technique referred to above. If the output frequencies are not required to be identical to the input frequencies, this filter also uses fewer modulators. By employing two carrier oscillators, any desired bandwidth may be obtained; the bandwidth and passband position may then be independently varied.