Royal RF-62

1. A depthsounder for use on a marine vessel to determine the depth of the water beneath it, comprising:

transmitter means for transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by the bottom limit of the water;

receiver means located in close proximity to the transmitter means for detecting acoustic information at the predetermined frequency, including reflections of the transmit pulses from the bottom limit of the water, the receiver means producing a corresponding return signal;

comparator means for comparing the return signal with a selected threshold and for determining the number of times the signal exceeds the threshold for each transmit pulse, thereby producing a return count for each transmit pulse; and

gain adjustment means for increasing the gain of the receiver means if the return count is zero and for decreasing the gain of the receiver means if the return count exceeds one, whereby the depthsounder is automatically adjusted to minimize interference.

2. A depthsounder as defined in claim 1, and further including the comparator means includes measurement means, operable whenever the comparator means determines that the return signal exceeds the selected threshold at least one time, for measuring the time delay between the transmitting by the transmitter means of each transmit pulse and the receipt by the receiving means of the corresponding pulse after reflection by the bottom limit of the water, to produce a bottom measurement. 

3. A depthsounder as defined in claim 2, and further including:

filtering means for filtering the successive bottom measurements to produce a filtered bottom measurement that is updated with each successive bottom measurement; and

display means for displaying the filtered bottom measurement.

4. A depthsounder as defined in claim 2, wherein the transmitter means includes means for adjusting the repetition rate of the transmit pulses as a function of the preceding bottom measurements. 

5. A depthsounder as defined in claim 2, wherein the comparator means includes means for enabling the determination of the number of times the return signal exceeds the selected threshold only during a time interval corresponding to a prescribed range of locations spanning the previous bottom measurement. 

6. A depthsounder as defined in claim 2, wherein the measurement means includes means for selectively adding or subtracting a predetermined offset to the bottom measurement, to account for the depth of the transmitter means and receiver means below the water surface. 

7. A depthsounder as defined in claim 1, and further including fish finder mode means for selectively conditioning the gain adjustment means so as to detect any fish in the body of water, the fish finder mode means selectively causing the gain adjustment means to increase the gain of the receiver means if the return count is zero and to decrease the gain if the return count is greater than two, wherein if the return count is two or more, all but the last count represent fish in the water. 

8. A depthsounder as defined in claim 7, wherein:

the comparator means includes measurement means, operable whenever the comparator means determines that the return signal exceeds the threshold at least two times, for measuring the time delay between the transmitting by the transmitter means of each transmit pulse and the receipt by the receiving means of the corresponding pulse after reflection by a fish, to produce a fish depth measurement; and

the depthsounder further includes display means for displaying the successive fish depth measurements.

9. A depthsounder as defined in claim 1, wherein the comparator means includes means, operable each time the return signal exceeds the selected threshold, for measuring the length of time it exceeds the threshold, and means for counting the number of times the signal exceeds the threshold for at least a prescribed time duration, to produce the return count for each transmit pulse, whereby the effect of noise on the successive return counts is reduced. 

10. Fish detection apparatus for use on a marine vessel to detect the presence of fish beneath the vessel, the apparatus comprising:

transmitter means for transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the transmit pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by any objects such as fish in the water and by the bottom limit of the water;

receiver means located in close proximity to the transmitter means for detecting acoustic information at the predetermined frequency, including reflections of the transmit pulses from any fish in the water and from the bottom limit of the water, the receiver means producing a corresponding return signal;

comparator means for comparing the return signal with a selected threshold and producing a return pulse each time the signal exceeds the threshold, the last return pulse associated with each transmit pulse representing the bottom limit of the water and any earlier return pulses representing objects such as fish in the water;

measurement means for measuring the time delay between the transmitting of each transmit pulse and the receipt of at least one of the resulting return pulses, if any, other than the last return pulse, to produce a succession of fish depth measurements;

alarm means; and

detection means for comparing each fish depth measurement with a prior fish depth measurement, determining that a fish is present in the water if the two measurements are within a first predetermined distance of each other, the detection means also actuating the alarm means when it determines a fish is present.

11. Fish detection apparatus as defined in claim 10, wherein the measurement means produces each fish depth measurement by measuring the time delay between the transmitting of each transmit pulse and the receipt of the corresponding next-to-last return pulse, if any. 

12. Fish detection apparatus as defined in claim 10, wherein the first predetermined distance used in the detection means is about four feet or 25 percent of the fish depth measurement, whichever is greater. 

13. Fish detection apparatus as defined in claim 10, wherein the detection means includes means for again actuating the alarm means only when the current fish depth measurement differs from the previous measurements by more than a second predetermined distance. 

14. Fish detection apparatus as defined in claim 13, wherein the second predetermined distance used in the detection means is about one-half foot. 

15. Fish detection apparatus as defined in claim 10, wherein:

the alarm means produces an aural signal; and

the apparatus further includes means for providing a visual display of the successive fish depth measurements.

16. Fish detection apparatus as defined in claim 10, wherein the comparator means includes means for producing a return pulse only when the return signal exceeds the selected threshold for a prescribed time duration, whereby the false production of a return pulse because of noise is reduced. 

17. Fish detection apparatus for use on a marine vessel to detect the presence of fish beneath the vessel, the apparatus comprising:

transmitter means for transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the transmit pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by any objects such as fish in the water and by the bottom limit of the water;

receiver means located in close proximity to the transmitter means for detecting acoustic information at the predetermined frequency, including reflections of the transmit pulses from any fish in the water and from the bottom limit of the water, the receiver means producing a corresponding return signal;

comparator means for comparing the return signal with a selected threshold and producing a return pulse each time the signal exceeds the threshold, to produce a sequence of return pulses for each transmit pulse;

bottom blanking means for disregarding any return pulses in the sequence following within a prescribed time period a preceding return pulse that was not disregarded, to produce a modified sequence of return pulses for each transmit pulse, the last return pulse in each modified sequence representing the bottom limit of the water and any earlier return pulses in the modified sequence representing objects such as fish in the water; and

measurement means for measuring the time delay between the transmitting of each transmit pulse and the receipt of at least one of the resulting return pulses in the modified sequence, if any, other than the last return pulse, to produce a sequence of fish depth measurements.

18. Fish detection apparatus as defined in claim 17, and further including:

means for comparing the successive fish depth measurments with each other; and

display means for displaying a fish depth measurement when two successive measurements are within a prescribed limited range of each other.

19. Fish detection apparatus as defined in claim 17, wherein the prescribed time period used in the bottom blanking means corresponds to a depth of about six to seven percent of the bottom depth plus about 3 to 3.5 feet. 

20. Fish detection apparatus as defined in claim 17, wherein the comparator means includes means for producing a return pulse only when the return signal exceeds the selected threshold for at least a prescribed time duration, whereby the false production of a return pulse because of noise is reduced. 

21. A method for determining the depth of the water beneath a marine vessel comprising steps of:

transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by the bottom limit of the water;

receiving acoustic information at the predetermined frequency, including reflections of the transmit pulses from the bottom limit of the water, the step of receiving including a step of producing a corresponding return signal using a receiver having an adjustable gain;

comparing the return signal with a selected theshold and determining the number of times the signal exceeds the threshold for each transmit pulse, thereby producing a return count for each transmit pulse; and

increasing the gain of the receiver if the return count is zero and decreasing the gain of the receiver if the return count exceeds one, whereby the method for determining depth automatically minimizes interference.

22. A method as defined in claim 21, and further including a step of measuring, performed whenever the step of comparing determines that the return signal exceeds the selected threshold at least one time, the measuring step measuring the time delay between the transmitting of each transmit pulse and the receipt of the corresponding pulse after reflection by the bottom limit of the water, to produce a bottom measurement. 

23. A method as defined in claim 22, and further including steps of:

filtering the successive bottom measurements to produce a filtered bottom measurement that is updated with each successive bottom measurement; and

displaying the filtered bottom measurement.

24. A method as defined in claim 22, wherein the step of transmitting includes a step of adjusting the repetition rate of the transmit pulses as a function of the preceding bottom measurements. 

25. A method as defined in claim 22, wherein the step of comparing includes a step of enabling the determination of the number of times the return signal exceeds the selected threshold only during a time interval corresponding to a prescribed range of locations spanning the previous bottom measurement. 

26. A method as defined in claim 22, wherein the step of measuring includes a step of selectively adding or subtracting a predetermined offset to the bottom measurement, to account for the depth below the water surface the steps of transmitting and receiving occur. 

27. A method as defined in claim 21, and further including a step of selectively modifying the steps of increasing and decreasing so as to detect any fish in the body of water, the step of increasing then increasing the gain of the receiver if the return count is less than two and the step of decreasing then decreasing the gain if the return count is greater than two, wherein if the return count is two or more, all but the last count represent fish in the water. 

28. A method as defined in claim 27, wherein:

the step of comparing includes a step of measuring, performed whenever the step of comparing determines that the return signal exceeds the threshold at least two times, the measuring step measuring the time delay between the transmitting of each transmit pulse and the receipt of the corresponding pulse after reflection by a fish, to produce a fish depth measurement; and

the method further includes a step of displaying the successive fish depth measurements.

29. A method as defined in claim 21, wherein the step of comparing includes steps of measuring the time duration each time the return signal exceeds the selected threshold, and counting the number of times the signal exceeds the threshold for at least a prescribed time duration, to produce the return count for each transmit pulse, whereby the effect of noise on the successive return count is reduced. 

30. A method for detecting the presence of fish in the water beneath a marine vessel, the method comprising steps of:

transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the transmit pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by any objects such as fish in the water and by the bottom limit of the water;

receiving acoustic information at the predetermined frequency, including reflections of the transmit pulses from any fish in the water and from the bottom limit of the water, the step of receiving including a step of producing a corresponding return signal;

comparing the return signal with a selected threshold and producing a return pulse each time the signal exceeds the threshold, the last return pulse associated with each transmit pulse representing the bottom limit of the water and any earlier return pulses representing objects such as fish in the water;

measuring the time delay between the transmitting of each trasmit pulse and the receipt of at least one of the resulting return pulses, if any, other than the last return pulse, to produce a succession of fish depth measurements; and

comparing each fish depth measurement with a prior fish depth measurement, determining that a fish is present in the water if the two measurements are within a first determined distance of each other, and actuating an alarm when it is determined a fish is present.

31. A method as defined in claim 30, wherein the step of measuring means produces each fish depth measurement by measuring the time delay between the transmitting of each transmit pulse and the receipt of the corresponding next-to-last return pulse, if any. 

32. A method as defined in claim 30, wherein the first predetermined distance used in the step of comparing is about four feet or 25 percent of the fish depth measurement, whichever is greater. 

33. A method as defined in claim 30, and further including a step of again actuating the alarm only when the current fish depth measurement differs from the previous measurements by more than a second predetermined distance. 

34. A method as defined in claim 33, wherein the second predetermined distance used in the step of comparing is about one-half foot. 

35. A method as defined in claim 30, wherein:

the alarm produces an aural signal; and

the method further includes a step of visually displaying of the successive fish depth measurements.

36. A method as defined in claim 30, wherein the step of comparing includes a step of producing a return pulse only when the return signal exceeds the selected threshold for at least a prescribed time duration, whereby the false production of a return pulse because of noise is reduced. 

37. A method for detecting the presence of fish in the water beneath a marine vessel, the method comprising steps of:

transmitting into the water a sequence of acoustic transmit pulses at regular intervals of time, the transmit pulses having a predetermined frequency and being transmitted in a generally vertical direction, whereupon they are reflected by any objects such as fish in the water and by the bottom limit of the water;

receiving acoustic information at the predetermined frequency, including reflections of the transmit pulses from any fish in the water and from the bottom limit of the water, the step of receiving including a step of producing a corresponding return signal;

comparing the return signal with a selected threshold and producing a return pulse each time the signal exceeds the threshold to produce a sequence of return pulses for each transmit pulse;

disregarding any return pulses in the sequence following within a prescribed time period a preceding return pulse that was not disregarded, to produce a modified sequence of return pulses for each transmit pulse, the last return pulse in each modified sequence representing the bottom limit of the water and any earlier return pulses in the sequence representing objects such as fish in the water; and

measuring the time delay between the transmitting of each transmit pulse and the receipt of at least one of the resulting return pulses in the modified sequence, if any, other than the last return pulse, to produce a sequence of fish depth measurements.

38. A method as defined in claim 37, and further including steps of:

comparing the successive fish depth measurements with each other; and

displaying a fish depth measurement when two successive measurements are within a prescribed limited range of each other.

39. A method as defined in claim 37, wherein the prescribed time period used in the step of disregarding corresponds to a depth of about six to seven percent of the bottom depth plus about 3 to 3.5 feet. 

40. A method as defined in claim 37, wherein the step of comparing includes a step of producing a return pulse only when the return signal exceeds the selected threshold for at least a prescribed time duration, whereby the false production of a return pulse because of noise is reduced.