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McGov: You have misunderstood the many (complex) problems and analogies: The Loco horn is the GROUND signal. Not EMI, not circuit noise, though these are a problem. Perhaps if I explain it in terms of 'real' signal levels it might be clearer. Let's invent a signal strength measure - the GeoVolt. It's like microvolt and millivolts, just easier to comprehend. With your coil in the air, do some tests with a US 10C dime. 1 cm below the coil, it gives a signal of 1000 GeoVolts. At 10 cm, it's down to 25 GeoVolts, at 20 cm it's at 2 GeoVolts, at 25 cm it's at 0.5 GeoVolts, at 30 cm it's at 0.2 GeoVolts. Now lower your search-coil until it's 15mm above some typical mildly mineralised ground. The signal from the ground is 10 GeoVolts. But it's not constant - swing your coil, it wobbles up and down from 9 to 11 GeoVolts, sometimes 8 or 12. Now I hope you see the problem. If you're looking for a 25 cm (10 inch) deep dime, you're looking for 0 to 0.5 to 0 signal, when all the time the ground is giving a 9 to 11 to 10 to 10.5 to 8.5 to 10 signal. So you can see the 30 cm (12 inch) deep dime is rather a challenge.
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If you dont want telling off from the boss, think about the question first !
The inband noise in these machines is miniscule - the Rx coil has no appreciable resistance so are low Johnson noise, the pre-amps are only a few nV/Hz noise. The I.F. BW is only a few Hz wide - so the noise contribution in this narrow BW is also very small. Win, win, win.
So why the struggle? - the elephant in the room is the ground signal return, which in relation the the noise generated in the Rx channels is massive.
The focus should be on the ground return signal - this is the dominant 'noise pollutant' - getting this to a minimum in real time allows the Threshold for detect to be reduced for a valid detect.
Again, to say "THE NOISE" does not mean anything.
It is more valid to say... Anticipated valid target return power / Ground return signal power. This is the S/N
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... and some other contributors. VLF band is a noisy place on it's own. Many of these "atmospheric" noises are received by ground loops, giving a false impression that these are "ground noises" while their true origin is ionosphere. The craziest signals of all are "whistlers". Above 30kHz situation becomes better.Comment
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Originally posted by Aziz View PostDave, you are trying to force me to take a lot of blue pills again. Don't you? *LOL*
But you are wrong with the "law of 64".
Hey, let's start the Metal Detecting Nobel Prize (MDNP).
Anyone, who solves this issue (incl. the math proof), will get a MDNP and will be very much respected on all the metal detecting forums.
Deal?
(I'm not allowed to contribute, I'm in the Nobel jury committee
.)
Cheers,
Aziz
F B Johnson already won the prize in 1956.
Read the rest in the full Johnson paper in the Pulse Induction History thread. He does say that the results are affected by the finite size of the object, which presumably means the distance at which the 6th power law kicks in for a given coil radius.
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He really deserves the posthumous Metal Detecting Nobel Prize (when I'm correct about his pass away).Originally posted by Ferric Toes View Post
Hats off to Johnson.
AzizComment
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And here's how to do the experiment yourself ->
MagFieldCoil.pdf
Quoting from section 11:
"Please leave the bench as you found it. Thank you"
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Thanks to ALL . . . I'm sure that I am not the only one fasinated by all of this but . . .
There's a question begging to be asked here.
Obviously ML has already figured a lot of this out ? So it's not impossible . . . just costly ?
They had to in order to be at the depths they operate in.
They own the deep . . . from what I have seen.
Not suggesting anything in violation of law so . . .
Why don't some of you folks band together ( is that possible ) . . . share knowledge, ideas, on a completely seperate project or open a completely new company away from the proprietary stuff you do now and do some meaningful experimental testing and validation. Not to catch up but to surpass. You are free to do this . . .
This stuff is your life . . . right? and no one person knows it all because there are parts of it you love and parts you hate. It's complex for sure but it still is not rocket science. Life is short and you only get one shot at this one.
I really don't know any of the details but . . . I wonder how Tom D. managed to put that 1266X MAGNUM together? and I wonder what did that unit actually achieve?Comment
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On this forum, there are some advanced projects ongoing in the IB/PI field, and some non-"traditional" PI methods are also showing promise.
A number of forum members are actively involved in companies designing metal detectors, and there are a few who are submitting leading edge patents and licensing/branching their work into companies.
It doesn't necessarily take any hyperbole and bursting visionary inspiration to motivate these people
A wild goose chase on various methods, tossing ideas left and right without necessarily testing them, can often be counterproductive. Some things can be said outright not to work all that well on a theoretical basis by people who are familiar with their subject matter, and it's polite to respect that. There sometimes are "groundbreaking" experiments, but those are usually not the sort where one just tosses everything at a problem and asks others to test it out in their stead.Comment
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OBD - Thank You . . . there is work being done! Well that is reassuring . . .
I have never seen this stated before:
"A number of forum members are actively involved in companies designing metal detectors, and there are a few who are submitting leading edge patents and licensing/branching their work into companies."
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IMHO the reality is rather different. This Forum is about as good as it gets, and again IMHO, that is pretty darn good. We have theorists, engineers, technical hobbyists, professionals, amateurs, digital and analogue, plus a few with a fuzzy logic syndrome, from countries all over the world freely contributing their knowledge and expertise to the advancement of metal detector technology. Even ML does not have it that good and the laws of physics apply to them as much as anyone else. Pulse Induction was around decades before ML as you can see from the PI History and Theory thread on Geotech.Originally posted by mcgov51 View Post
Surpass in what? there are so many applications of metal detectors, and PI technology in particular, many of which ML are not involved in. e.g. archaeological survey, underwater pipline survey, boat towed marine, professional diver use, general industrial (recycling, timber, mining and quarrying, food protection, injection molding protection, chipboard manufacturing, monitoring blast furnace slag).....the list goes on.
I have done basic research, had my own companies, been employed by companies, and now act as independent consultant, plus still researching soil magnetism and ways of achieving better ground cancellation. It has been my life, and after 47 years in metal detection it still is a major interest, but I now value working on my own, in my own time and sharing knowledge with others on a forum such as this. To go further would only add complication, and as you say, life is short.
Many contributors have a day job - telecomms, software development, radio technology, industrial design, and have no desire to be part of a new business, particularly in todays economic climate. But metal detection for them has a fascination as a serious hobby and I guess that is how it will stay. Being this way does not preclude major breakthoughs and new techniques. Look at other disciplines, astronomy, geology and general electronics too, where much advancement in knowledge has been the work of amateurs.
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Very interesting, this ECDO stuff. Not widely known under that name, but in some (non-English) literature something similar is mentioned as ALL (Amplitude locked loop) method. Technically, oscillator, operating on the edge, amplitude controlled by very precise ALC loop. When metal object is near, amplitude drops due to absorption, then loop compensate by increasing bias or something, this signal from loop response is target indication. Is that? If it is, at first glance may look modern like bronze spear, but I witnessed very amazing performance in some industrial applications, even one ear-dropping device, operating thru concrete wall, registering just movement of thin foil membrane and picking up audio this way. Not bad at all (for ALL, or ECDO if this is the same thing).Originally posted by Dave J. View PostComment
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Ferric Toes - Well said . . . well said indeed . . . anyone who reads
what you said . . . can feel the compassion you have for this hobby.
You were not even tempted to make one nasty comment.
BRAVOComment
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"Digital" obviously gets over-used these days.
You need to remember that "digital" systems are really made from analog parts. The line can be quite blurred between the two at times. While digital has it's advantages, it also has compromises, you just need to determine if it is worth it depending on the application.
Example: Purists still trump the sound quality from true analog devices like record players, despite the obvious downfalls of records. The mass consumer market prefers digital storage (iPods etc) for obvious reasons and thinks digital sounds good enough, or are at least willing to tolerate it because they can store it invisibly.
I suspect the break through that you are interested in involves an analog system, rather then digital. With analog signal, you can continue to zoom in on or work your "filters" on a signal, with digital if you zoom in the "picture" or sample appears to be worse, therefor you need more digits, hence the cat and mouse chase that digital known for.
No matter how "big" your digital sample or picture is, it always falls short on information when compared to the true analog picture.Comment
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While i agree with penny packer most of the time i have to disagree here, the future is digital for the consumer market anyway simply due to security issues.
Digital should not be thought of as emulating analogue, thats far too simplistic.
In some ways digital adds a layer of protection(software) that analogue frankly cannot match.
Hobbyists,home builders and such should not be ruled out either, sometimes engineers can be too close to a problem to see the answer clearly.Comment
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PennyPacker / sinclairuser - I am not steadfastly sold on anything . . . I am just trying to float ideas for those, who know? . . . to consider.
It's not how much you know . . . It's how much you care that matters ?
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