Adjustable and selective electrical filters and methods of tuning them
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United States of America Patent
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Nov 22, 1983
Grant Date -
N/A
app pub date -
Feb 6, 1981
filing date -
Feb 11, 1980
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A notch filter is provided with an ancillary circuit including a non-inverting amplifier and a coupling which enables the filter to form part of an oscillatory loop of which the frequency of oscillation corresponds to the frequency of maximum rejection by the notch filter. Measurement of that frequency facilitates the tuning of the notch filter, which includes capacitors constituted by varactor diodes. The gain of the ancillary circuit may be adjusted to change its mode of operation from oscillation to that of a tuned amplifier so that a sweep of the center frequency of the notch filter through a range of interest facilitates a search for an unknown interfering frequency and the simultaneous tuning of the notch filter to reject that interference.
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