FIELD: electronic communications; programmable intermediate-frequency passband for different modes of communications.
SUBSTANCE: programmable intermediate-frequency passband is obtained in receiver or transmitter when using fixed-passband filters. At least two intermediate frequencies are used. Filter operating at each intermediate frequency has fixed passband equal to or wider than desired one. Heterodynes are tuned to convert useful-signal frequency to frequency shifted to one passband boundary of fixed intermediate-frequency filters. First mixer and heterodyne shift useful signal to one boundary of first fixed intermediate-frequency filter. Second mixer and heterodyne shift filtered-off signal to opposite boundary of second intermediate-frequency filter. Desired frequency band is obtained in the form of total useful signal frequency shift from closest passband boundary of first intermediate-frequency filter and useful signal frequency shift from opposite boundary of second intermediate-frequency passband.
EFFECT: provision for specifying common requirements to intermediate-frequency passband for different modes of communications.
14 cl, 6 dwg
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