Adjacent channel interference detection & suppression circuit
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United States of America Patent
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-
Feb 20, 1996
Grant Date -
N/A
app pub date -
May 31, 1994
filing date -
Jun 11, 1993
priority date (Note) -
Expired
status (Latency Note)
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Abstract
FM radio receivers, particularly in moving vehicles, are subject to intermittent adjacent-channel interference. It is known to detect such interference and suppress it by narrowing bandwidth in the Intermediate Frequency (IF) signal path. However, it is desirable to again broaden the bandwidth once the interference has subsided. An improved system, which automatically and dynamically adjusts the bandwidth, employs first and second signal level evaluation circuits (11, 12), a comparison stage (13) which compares their outputs, and a variable-bandwidth filter stage (6, 14) controlled by the comparison stage. The comparison stage is programmed with a set of signal difference threshold values and corresponding filter bandwidth values, and controls the filter stage (6, 14) to adjust the bandwidth to the appropriate value, indicated by which signal difference threshold value has been exceeded. In a preferred embodiment, a second IF filter (15) does 'double duty' as part of the variable-bandwidth filter stage.
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