As will quickly become apparent, I know nothing about depth/fish finders.
My question: Is there a minimum focus distance? Angle of detection?
It seems these work on the same principle as livestock pregnancy scanners. And cost about a quarter as much.
Anyone with experience in one or both?
You might take a shot at asking on some of the sci.electronics groups. When I was looking for specific transducer info on the 'net (several years ago), I couldn't find squat. Certain transducers have an emission angle spec, which I assume is generally a cone shaped pattern.
I've looked at published specs for some of these units, and I assume that you know about the ultrasonics and transducers. Ultrasonics have many uses, and the fish sonar units are capable of high peak power levels. Medical units for muscle or tissue therapy are capable of causing tissue damage if used incorrectly, although I don't have any idea what the output power is for this type of equipment.
I doubt that a fish sonar would be effective for imaging since the display resolution is very poor, more along the lines of early pong-type TV video games (and only slightly better for the high end CRT type displays).
From an old post concerning ultrasonics.. Some of these (fish sonar) units are capable of producing in excess of 1 kW of peak output power.. i haven't heard any stories of anyone sustaining injury from careless use of this type of equipment, but i believe it could happen. For example, Navy divers can be seriously injured if pinged by a ship's sonar.
I wouldn't recommend placing a transducer against your body, to try to feel if there is any output from the transducer. The lyrics "You shake my nerves and you rattle my brain".. may be a representation of the possible effects.
excerpt from a recent thread about generating ultrasonics.. Anxiety, discomfort and pain are likely to be the effects from strong emissions of certain frequencies of ultrasonics. Ultrasonics can produce disturbing effects to tissue and body fluids. Loud audible audio can rattle the eardrums at an uncomfortable rate/level. Ultrasonics can be (are) used for muscle therapy, when an emitting transducer is placed on the skin. This could also inflict damage to tissue at excessive levels. This transducer is basically the same element that echo fish finders use. An article that was published years ago concerning the basic principle and effectiveness of ultrasonic pest repellers, described the physical effect as cavities that are created in the bug's brain fluids at certain ultrasonic frequencies.
Ultrasonic welders have been used for joining vinyl or plastic products.
WB ..............
Wow! This sounds like our Secretary of Defense's "unknown unknowns". I didn't know how much I didn't know. Thank you.
I can see I am in way over my head. Cheaper to buy than do the R&D.
But why haven't we seen the headline "Fishermen use ultrasound to scramble fish brains so they are easier to catch."
Dolphins actually do this AIUI. However, fish are generally far too far away for them to be affected at all. The power generated is a few watts-killowatts. Once you get a few dozen meters out or so, the power is quite small, as the beam has spread out so much.
Kind of like a 1Kw laser can be used to cut metal, but a 1Kw floodlight will just make it a little warm at the same distance.
Not OT at all. Drop a lead (metal...right?) weight. Use an underwater mic to measure the times until the fish yell..
**************************************************** sorry remove ns from my header address to reply via emailImagine a _world_ where Nature's lights are obscured by man's. There would be nowhere to go. Or wait a while. Then you won't have to imagine.
Frieshwater fishing sonars operate in the general vicinity of 200 KHz while imaging sonars for medical use operate at MHz frequencies. Higher frequency affords better resolution, smaller xdcrs and sharper beams but significantly reduces range -- which isn't an issue in medical and inspection applications.
Minimum distance is determined by the length of the transmit pulse plus any post-pulse ringing because the same xdcr is used for xmit and rcve. Min range on my fishing sonars is a foot or so.
They can detect small objects at some distance in water. They can "see" a 1/8" oz jighead (about the size of a pea) in 20 feet of water They can resolve to within an inch or less in depth but diverse targets "in the cone" at the same depth cannot be differentiated.
Cone angles are typically 12 to 20 degrees.
Don't worry about the claimed peak power ratings. The dutycycle is very short; average power is only a few watts. They typically draw less than an amp from the 12-volt battery.
I think Ive got a portable unit kicking around, but its the multiple line doppler type..shows a bright line for the bottom and a secondary line higher up for any object above the bottom. Like very early radar IIRC.
Gunner
"No man shall be debarred the use of arms. The laws that forbid the carrying of arms disarm those only who are neither inclined nor determined to commit crimes. Such laws make things worse for the assaulted and better for the assailants. They ought to be designated as laws not preventative but fearful of crimes, produced by the tumultuous impression of a few isolated facts, and not by thoughtful consideration of the inconveniences and advantages of a universal decree." - Thomas Jefferson
Not "focus" per-se. There usually exists a "blanking interval" to prevent transmitted ringdown from saturating and spoofing the the receive channel. Meaning: you can't use in very shallow water, like 1 foot or so. In the ultrasonic frequency range, the acoustic far field (where "focusing" becomes eseentially a plane wave) is a foot or so too.
Depthfinder: very narrow beamwidth or angle of detection so you get an accurate, tight "spot" (acoustically) reflected from the bottom.
Fishfinder: broader beamwidth since you want to catch echos from the fishes, not shot narrow acoustic beams in between them.
Errrr. no. Only similar in that both systems transmit a pulse and listen for echos. But so do radars, and seismic profilers, and lithotripsy devices, but I wouldn't hook those up to a cow. (Not unless I wanted to cook my steal in-situ!)
I design and build sonars and acoustic systems.
Cheers,
John
Similar question: Can a fish finder operate in air.
I have wondered if a fish finder could be used to sense objects behind a vehicle when backing up. Will this work? chuck
Yes. But only if it rains really, really hard.
seriously, yes. sonic level moniters were/are? used in grain elevators. sonar has been used in industry for many years for ranging.
i worked briefly for WesMar in Seattle, they had an industrial level monitering division and a Marine division. they tested some things right in the parking lot. you didn't want to be outside when they were running a Marine transducer. the industrial ones were bad too, if you got in the line of fire. --Loren
The transducer has to be designed for the medium it's going to work in. Air is some thousand times less dense than water, and does not transmit high frequencies well. A fish finder will not work in air, I'm not sure if it might be damaged by the attempt.
i am only reporting on my direct experience. ymmv, --Loren
Can anyone say, Polaroid camera? :-) ...lew...
A number of cameras used sonic range finding as well. Polaroid comes to mine.
Gunner
No 220-pound thug can threaten the well-being or dignity of a 110-pound woman who has two pounds of iron to even things out. Is that evil? Is that wrong? People who object to weapons aren't abolishing violence, they're begging for the rule of brute force, when the biggest, strongest animals among men were always automatically "right". Guns end that, and social democracy is a hollow farce without an armed populace to make it work. - L. Neil Smith
You can use sonar in either water, or air.
However, you have to design the unit to work in one. Dolphins can't detect flying insects, and bats can't hunt tuna.
the Marine xducers that were tested in air could take out your hearing if you got too close and was uncomfortable at 100 feet in front. i don't know for sure what exactly the design guys were doing, but they did it quite often.
they certainly were getting echos, that was the main reason for their setup. i suspect they were working on the ranging circuits. certainly they had to compensate somehow for the medium (air), possibly a large difference in the speed of sound and signal strength. --Loren
Fish finders do work in air, but range is very limited.
Robotics enthusiasts use ultrasonic ranging quite a bit. Do a google on ultrasonic rangefinder. There are lots of schematics and ideas out there.
National Semiconductor used to offer a rangefinder chip, LM1812.. If you can find one, a suitable transducer for air might be:
We built an industrial rangefinder in the mid-80's that could detect a pin at a range of 1 meter. We used Massa xdcrs.
Ultrasonic rangefinders (for use in air) are available commercially. See, for example,
We built
More importantly, the distance calibration will be grossly wrong since the speed of sound in air is different than the speed of sound in water.
Gary
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