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Got to be a reason. Fish finder vs metal detector
Posted by: Dancer
Date: August 31, 2017 06:38AM
Got a inexpensive fish finder. No trouble detecting fish down to 30 feet, maybe more. Metal detectors fighting to get past a foot.
(Mostly) I know most fish are bigger than a quarter, but anyone got a detector that can air test a aluminum can at 5-10 feet?
Now I'm talking coin shooting not the industrial machines. Ya got to admit the fish finders can get you a ton of information for around 4-5 hundred bucks. Where as its a big deal for a back light to be included on most detectors. Just saying.

Dancer

Re: Got to be a reason. Fish finder vs metal detector
Posted by: Dave J.
Date: August 31, 2017 08:52AM
Fish finders and metal detectors both work on a transmit-receive principle, but that's all they have in common. Metal detectors work by AC magnetic field dipoles and the signal power vs. "depth" is negative twelfth power. Fish finders are sonar and the signal power vs. "depth" is negative 4th power.

The reason we don't do metal detection by sonar is because soil does a terrible job of transmitting sound. Water on the other hand does a superb job of transmitting sound.

Funny historical note: the VLF induction balance discriminator was patented in the late 1800's as a benchtop unit for distinguishing counterfeit coins from genuine. This was before the invention of the vacuum tube, the thing was entirely electromechanical. But underwater echolocation and imaging is even older than that, cetaceans have been doing that for millions of years.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: Dancer
Date: August 31, 2017 09:19AM
Quote
Dave J.
Fish finders and metal detectors both work on a transmit-receive principle, but that's all they have in common. Metal detectors work by AC magnetic field dipoles and the signal power vs. "depth" is negative twelfth power. Fish finders are sonar and the signal power vs. "depth" is negative 4th power.

The reason we don't do metal detection by sonar is because soil does a terrible job of transmitting sound. Water on the other hand does a superb job of transmitting sound.

Funny historical note: the VLF induction balance discriminator was patented in the late 1800's as a benchtop unit for distinguishing counterfeit coins from genuine. This was before the invention of the vacuum tube, the thing was entirely electromechanical. But underwater echolocation and imaging is even older than that, cetaceans have been doing that for millions of years.[/quote

Dave, glad for your expert input. My question was way above my pay grade.
Along the lines though, does it seem to you the fish/sonar units have progressed much faster than our detectors?
I was reading up on one that claims to be able to see your lure, while stationary of course. Than all the graphics and reduction in prices. Pretty amazing.


Re: Got to be a reason. Fish finder vs metal detector
Posted by: Dave_E
Date: August 31, 2017 10:31AM
There are fish finders that can see a teardrop size lure, while moving, while ice fishing.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: Tom_in_CA
Date: August 31, 2017 11:14AM
Dancer, to the degree that sonar fish finders (and cell phones and computers, etc....) have seen more advancements than metal detectors, is d/t the laws of physics Dave was telling you about. No amount of "smaller and faster" electronics, and nothing that sonar-fish finders do, will change the fact that soil (terra firma) is extremely difficult to see through. Versus water, which is easy to see through. You can't change the laws of physics.

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Re: Got to be a reason. Fish finder vs metal detector
Posted by: still looking 52
Date: August 31, 2017 12:12PM
Not sure I would want a metal detector that could detect down five feet, that's like digging a grave. There could be some commercial reasons for a machine like that but not for the average metal detector.
Talking about sonar, the Navy is still trying to get sonar as good as a dophin but hasn't got there yet.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: Flintstone
Date: August 31, 2017 02:20PM
If a detector could go 5' and could tell what you were looking at, I would dig 5' for a 20.00 gold coin or two.

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However I do recall an article in a UK mag, "Treasure Hunting" I think, where some sonic device
Posted by: vlad
Date: August 31, 2017 02:36PM
was used to find the bodies of some Scots killed--I think during the time of Robert The Bruce. I believe a transponder was used along with water to make the transmission work.
Some type of image on a screen showed skeletons, accoutrements and weapons--so there is something to it.
Whether ultrasound or what, I just don't recall.
The bigger problem with metal detectors is the amount of unwanted targets to be found--or a straight P.I. of high power would be the end all of finding things.
(Go to Nasa Tom's Forum and read his articles on "The Painful Truth" (about masking) in his hunts on some forts from the Seminole Wars....you will see what I mean)

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Eric Foster has stated that an orthongol loop can easily be made for a P.I.
Posted by: vlad
Date: August 31, 2017 02:43PM
which will go so deep (in bad ground) you need a backhoe.
The problem though is it is for large targets and has no resolution on a coin {s}.
The same holds true on constant wave (TR) units.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: ROBOCOP
Date: August 31, 2017 05:28PM
Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.

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Re: Got to be a reason. Fish finder vs metal detector
Posted by: bootyhoundpa
Date: August 31, 2017 05:58PM
Ground penetrating rader might give you a little extra depth,lol.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: Dancer
Date: August 31, 2017 05:59PM
Quote
ROBOCOP
Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.

Wow, now ain't that something! Some pretty smart cookies on this site.

Re: Got to be a reason. Fish finder vs metal detector
Posted by: stephenscool
Date: August 31, 2017 09:57PM
Quote
ROBOCOP
Magnetometers technology is also very interesting. Whirling electrons excited in a inert gas by a electrical charge and than start to settle down when the power is turned off

and the electrons try to realign with the earth's magnetic field. If there is ferrous iron in the area it will interrupt their natural realignment. This interruption is recorded and that's how you find a iron cannonball at 10 to 12 feet.

Something like that.
A lot of potential in something like this. It,could be used a discriminator in a pi. The idea needs some tweeking and trial and error though... lots of potential

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Finding a projectile is not the problem .....its the recovery :biggrin:N/T
Posted by: vlad
Date: September 01, 2017 05:32AM

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Magnetometers
Posted by: Tom_in_CA
Date: September 01, 2017 09:48AM
Quote
ROBOCOP
Magnetometers technology is also very interesting. ....

Magnetometers are only for finding iron. But the metal detector hobbyists , as you know, TRY THEIR DURNDEST NOT to find iron. :rolleyes: We all go out of our way to reject iron. Unless, of course, you're looking for 5 ft. deep iron cannon-balls I suppose. Or scanning the ocean floor for shipwreck sites.

But for the casual metal detector, they are of no use. Unless you're objective is to dig the most nails you can find ? If so, then you really don't even need a "magnetometer". You merely turn on your detector, put it into all-metal mode, head out to the nearest ghost town or cellar hole. Then I GUARANTEE you that you will no shortage or iron to choose from :)



Edited 2 time(s). Last edit at 09/01/2017 09:49AM by Tom_in_CA.

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