Communications – electrical: acoustic wave systems and devices – Echo systems – Presence or movement only detection
Patent
1982-09-29
1985-08-27
Swann, III, Glen R.
Communications, electrical: acoustic wave systems and devices
Echo systems
Presence or movement only detection
43 171, 340573, A01K 9712, G08B 2100
Patent
active
045382492
ABSTRACT:
A directional Doppler fish movement detector uses a relatively low ultrasonic frequency to minimize particulate scattering and absorption losses in turbid lakes and streams. The low ultrasonic frequency also minimizes Doppler noise caused by boat drift and wave action. To compensate for the relatively low frequency Doppler signals which result, including sub-sonic Doppler signals from slow moving fish, means are provided for doubling, or otherwise multiplying, the frequency of the Doppler signal to improve audibility. Means are also included which allow the relatively wide beam of the Doppler fish movement detector to be directed over a wide horizontal angle, and in one of the preferred configurations, the transducer assembly is attachable to the underwater portion of an electric propulsion motor so that the ultrasonic beam is directed along the line of thrust. Although useful for the detection of normally swimming fish, a preferred use is in cooperation with a fishing effort in which otherwise inactive fish are provoked into impulsive and detectable movements by bait casting into the area covered by the relatively wide ultrasonic beam.
REFERENCES:
patent: 3123798 (1964-03-01), Holloway et al.
patent: 3879697 (1975-04-01), Richard
patent: 4337527 (1982-06-01), Delagrange et al.
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