Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Patent
1985-10-31
1989-03-14
Blum, Theodore M.
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
455307, G01S 124
Patent
active
048128511
ABSTRACT:
Undesired, intefering narrow band received signals in a radio receiver are automatically cancelled by a cancellation system including a variable narrow band pass filter that separates a sample of the undersired signals from the total received signal, reverses phase of the sample and combines it with the total received signal, substantially cancelling the undesired signals therein. In a Loran-C receiver, desired beacon signals in the band 90 to 110 KHz are received aling with narrow band interfering (undesired) signals. During a "cancel mode," a narrow band of the total received signal is sampled by a variable narrow band pass filter and the narrow band sample is reversed in phase and then combined with the total received signal to cancel the undersired signals therein. The frequency of the variable narrow band pass filter is controlled by a pass filter control signal that is established during a "search mode" as the control signal at which a high (or maximum) interference signal is detected in the pass filter output. During the cancel mode, that control signal sets the frequency of the variable narrow band pass filter causing the interfering signal to be cancelled. Thus, interference detection during the search mode is accomplished using the same variable, narrow band pass filter as used during the cancel mode to cancel the interference.
REFERENCES:
patent: 3281698 (1966-10-01), Rose, Jr. et al.
patent: 3744015 (1973-07-01), Marimon et al.
patent: 4539566 (1985-09-01), Sharpe et al.
patent: 4549312 (1985-10-01), Michaels et al.
IEEE Standard Dictionary of Electrical and Electronics Terms, 3rd Edition, 1984, pp. 22 & 621.
J. Kalb, Georga Institute of Technology, EEE, Feb. 1971, p. 61, "A Novel Active Filter".
Blum Theodore M.
Digital Marine Electronics Corporation
Dunn Robert T.
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