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Detector history question :
Posted by: Tom_in_CA
Date: November 24, 2018 09:35AM
Even though detectors have been around since the 1930s (and even earlier), yet all the early decade's machines were only capable of finding large sized objects. Not coin sized objects.

So for example, even though Fisher Co. perpetually touts that they've been around since the mid 1930s, that was all just 2-box style. And even to the extent that they had some conventional rod-&-loop styles by the late 1950s (?), yet even those would have been hard-pressed to find coin-sized targets.

So all the early kinds might have been fine for finding land-mines or caches, or industrial/commercial purposes (eg.: hubcap and jar and pipe sized items), yet were not sensitive enough to find coin-sized items.

When did that change ? What were the first machines (in common use that is, not fluke experimentals) that could do it ?

I read somewhere that there was a certain mine detector that came out during the Korean conflict (very early '50s) that was indeed capable of finding coins. Like to get a quarter at a good 6" or something (albeit probably a bear to keep balanced). And even though it wasn't designed for that purpose, yet it was capable of doing it, if someone had wanted.

But barring a few fluke stories like that, you really don't see the hobby of hunting for individual coins taking off till the early 1960s. And even then-so, very geographically limited. Entire areas of the USA never saw a detector in their parks and schools till the late 1960s or early 1970s.

So what is the earliest accounts of coin-hunting that you've heard of ? And what machines were they using ? And what were they capable of ?

Here in CA, I talked to a guy who had graduated from High School, in Napa, CA, in 1959. He distinctly recalled seeing a fellow with a metal detector in one of the old parks there. And distinctly recalled that he was still in High school at the time (hence it was '58 or '59-ish). He stopped and watched the fellow for a bit. And distinctly recalled that he was digging coins (ie.: not just big targets). He could not recall what machine the guy was swinging though. Years later, in the late 1960s, or early '70s, he recalled that encounter, and went to get a machine of his own.

ITMD
Posted by: kt315
Date: November 26, 2018 03:36PM
do you have ITMD copy?

Re: ITMD
Posted by: Tom_in_CA
Date: November 26, 2018 09:21PM
uuuhhh, what does ITMD stand for ? :shrug:

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Re: ITMD
Posted by: Elton
Date: November 27, 2018 10:35AM
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Tom_in_CA
uuuhhh, what does ITMD stand for ? :shrug:

I wondered that too !! ???????????????????????????



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Re: Detector history question :
Posted by: vito
Date: November 27, 2018 01:17PM
Hello.
Think kt315 is talking about >> inside the Metal Detector <<.

All the Best

Re: Detector history question :
Posted by: Tom_in_CA
Date: November 27, 2018 09:26PM
ok, thanx. Maybe that's it. Does Carl's book dedicate much space to the question of the years/machines in which coin hunting became possible for detectors ? (as opposed to only large objects)

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Re: Detector history question :
Posted by: vito
Date: November 28, 2018 06:05AM
Hello Tom.

Why not sending Carl-NC a p.m. asking him self for some details?
Personally I didn't read the book but may be Santa will bring a copy this year. Ho Ho Ho...

All the Best & Good Luck

Re: Detector history question :
Posted by: Joe(TX)
Date: December 25, 2018 04:29PM
The earliest detector that was of the rod and round loop design was probably a mine detector...not very sensitive to coins during WW11 but the design was out there. Later the concept of the rod and round loop design was probably copied and made lighter by either Fisher with their T-10 and the White's had a model with 2 meters maybe called the Prospector. There may have been another rod and round loop design with another now obsolete detector manufacturer but the name escapes me for me now.

Re: Detector history question :
Posted by: Tom_in_CA
Date: December 25, 2018 08:07PM
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Joe(TX)
The earliest detector that was of the rod and round loop design was probably a mine detector...not very sensitive to coins during WW11 but the design was out there....

thanx for your input Joe.

To my knowledge, those used for WWII (at least the ones Americans made) could not pick up any items smaller than a soda-can sized. And even at that ... quite clumsy. Difficult to keep balanced, not consistent, etc...

From what I heard, it wasn't till the Korean war that a mine detector was made that was sensitive enough to find coin sized targets. Naturally, that wasn't its intended purpose. It was designed to find landmines, of course. But I just read somewhere that it was noted that it was sensitive enough to pick up a USA quarter to something like 5 or 6" or whatever.

There are also accounts of how the fellow who started Kellyco, who was operating those Korean conflict mine-detectors, used that type , for hobbyist purposes, when he got back to civilian life. And he did indeed find coins. Also CW hunters adapting that Korean era detector listed "bullets" among their finds. If it could find bullets, then, obviously coins are about the same size.

Even though that would push the ability to do "coin-shooting" to as early as the early 1950s, yet ... it was not till the early 1960s, at the earliest, that it caught on in any appreciable #'s. There might have been some geographic exceptions to this. But I know that even up to the early 1970s, there were tales of virgin parks and schools in some geographic areas.

Re: Detector history question :
Posted by: Dave J.
Date: December 26, 2018 12:43AM
Even the best BFO's couldn't do much. But, with silver coinage and sites not having been previously searched, even 3 inches of depth was enough to be useful.

The high frequency induction balance so-called "TR's" started to get popular I think late 50's - early 60's. Good ones will go maybe 5-7 inches in light mineralization and do a good job of knocking out iron. Unfortunately iron mineralization really cuts your depth. However (apart from ground balanced PI units) they're still the best machines for "bed of nails" iron infested sites.

The big game-changer was VLF with ground balance. They've been around since WW2, but didn't have appreciable impact on the the hobby market until the early 1970's. Most of those early units would air test in the 7 - 9 inch range, and when ground balanced would do nearly as well in most soils.

VLF-TR discrimination soon followed, not nearly as good as high frequency TR but still useful. The early 1980's saw the introduction of motion discriminators based on multiplying two second derivative signals, which is the foundation of VLF metal detector technology even today.

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Re: Detector history question :
Posted by: u2robert
Date: December 26, 2018 07:10PM
Look at the big brain on Dave J. thanks for the info


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Dave J.
Even the best BFO's couldn't do much. But, with silver coinage and sites not having been previously searched, even 3 inches of depth was enough to be useful.

The high frequency induction balance so-called "TR's" started to get popular I think late 50's - early 60's. Good ones will go maybe 5-7 inches in light mineralization and do a good job of knocking out iron. Unfortunately iron mineralization really cuts your depth. However (apart from ground balanced PI units) they're still the best machines for "bed of nails" iron infested sites.

The big game-changer was VLF with ground balance. They've been around since WW2, but didn't have appreciable impact on the the hobby market until the early 1970's. Most of those early units would air test in the 7 - 9 inch range, and when ground balanced would do nearly as well in most soils.

VLF-TR discrimination soon followed, not nearly as good as high frequency TR but still useful. The early 1980's saw the introduction of motion discriminators based on multiplying two second derivative signals, which is the foundation of VLF metal detector technology even today.


Re: Detector history question :
Posted by: Tom_in_CA
Date: December 27, 2018 11:33AM
Quote
Dave J.
.... The early 1980's saw the introduction of motion discriminators based on multiplying two second derivative signals, which is the foundation of VLF metal detector technology even today.


1977, to be exact. That was when Reb Baron first advertised their "SPD". Soon to be followed, in 1978, by Whites and their 6000D

But it's probably just as accurate to say "early 1980s". Because it took another year or two to catch on anywhere. Evolution (acceptance within md'ing ranks) was much slower to evolve in those days. D/t there was no internet lightening-fast communication/comparisons.

Also, since the way the motion discriminators were swung was SO counter-intuitive, there was initial reluctance, on many people's parts, to adopt them. So despite their technical introduction in 1977 to '78, the first I ever recall actually seeing on in-the-field, was about 1980. And initially, we laughed at the guy behind his back. Since it was obvious he was swinging the coil wrong. But ... after we saw his silver tallies from the worked out parks, we stopped laughing, and quietly went out and bought our own motion discriminators. Doh !

Re: ITMDN/T
Posted by: alex74
Date: January 04, 2019 06:18PM

(This message does not contain any text.)

Edited 1 time(s). Last edit at 01/04/2019 06:19PM by alex74.

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The only time I've ever seen that referenced is about a medical group that uses cloud sharing.N/T
Posted by: vlad
Date: March 10, 2019 08:16AM

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Re: Detector history question :
Posted by: Confetrit
Date: March 11, 2019 10:42AM
My very first MD was a surplus WWII mind detector. At age 13 this thing weighed about as much as I did back in 1969. I dug my first relic ever with it, a blown piece of Hotchkiss artillery shell. I still have this piece in my display case.

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