Cache Test

[mikebg]

64th addition to Murphy's law for the world vileness

The 63th addition to Murphy's law is: "In theory there is no difference between theory and practice, but in practice there is."

To rediscover the 64th addition, you need 64 identical coins and metal detector with TX coil placed inside the search head. Set with AIR TEST how deep the metal detector can detect a coin. Then check the following addition to Murphy's law for the world vileness:
"In no way to arrange 64 identical coins, the metal detector won't find them at twice the depth (than it can detect a coin :-)."
NOTES:
1. If you put coins in a metal container, you must put a coin in the same container when determining the detection depth :-)
2. You can make with coins a large eddy current circumference, but it is not allowed to solder them.
3. The law has not been tested with the orthogonal configuration of coils, because my big coils can not detect coins at all.
4. The law has not been tested with a large placed on the ground TX loop, because I do not have a suitable metal detector. However, soon we will do a test because we know a treasure hunter who uses SuperScan, designed by Eric Foster.

[Funfinder]

Phew, great thread - i read since 2006 ehm since all 8 pages!


Can try that test with Jeohunter if my coins have 1kg alltogether.

But what I miss is the shape of the cache - we need a fixed defintion:

diameter exactly 10cm (4inch) - is this OK?

Or should we put the coins into a plastic bag so it's like a little ball?

The more spreaded (flat) the cache the more depth detection -
I guess this will be the same like with thin alu-foil.

As for P.I. best result would be with a 45-50cm coil (18-20").

@ joejoe

07-17-2011
> but do not have the bucks for lorenze or something of that nature, so just moderate
> depth like two feet. I have red clay and lava rocks. Maybe I could try some of the ones
> mentioned of the vlf's that came close and make do until I get some $'s, better than
> nothing (maybe).


You could try this one:

http://www.nexusdetectors.com/Nexusc...ldetector.html

This is the "simple version" of the 3500 Euro expensive Nexus Ultima but it costs just
400 Euro (perhaps 600 dollars at your island). It uses also induction balance like the
Jeohunter and it works for black sand and red clay as described. Depending on the
coil size you should get good results.

btw the bulgarian P.I. Ground Pioneer 4500:
http://www.deeptech-bg.com/gp4500.html

read page 4-5 of the manual for the depth with 1m frame and 50cm coil:
http://www.deeptech-bg.com/gp4500/GP4500.pdf

price of this pi is around 1200 Euro outside bulgaria.


I'm shure it's possible to find such 1kg coin-cache but first we
need to define an excact shape of it's appearance and size.

[Qiaozhi]

MikeBG is referring to the fact that you need to increase the TX power by 64x to double the detection depth for a given object (e.g. a single coin). One twist on this idea would be to increase the target size by 64x. However, simply putting 64 identical coins in a pile will not work. This is because you do not have a 64x larger target, but a collection of 64 similar ones. Unless you electrically connect all the coins into a flat sheet, or melt them down to form one very large coin of the same thickness, the eddy currents will still flow in small circles within the individual coins, and there will be no doubling of detection depth. This is why the cache is harder to find than you might intuitively expect.

[joejoe]

I tested several std PI detectors, like Sea Hunter, Infinium, SandShark, SMPI... the only thing that came close was the TDI with a custom 24" coil, which could see the cache in an air test. But I did not properly shield the coil, and it was too noisy in the ground. I did not have any of the big-loop PI detectors to try.

I have since moved, had to retrieve the cache, and have not re-buried it.

- Carl

Everytime I read that I am reminded of those story that go something like this: Once there was a man who was testing his detectors and he buried a jar full of silver. None of the detectors could find it and suddenly something unfortunate happened to him before he could recover it..... People have searched and searched and it is still there to this day!

Who left the video of the tdi and the 1x1 coil? Geo? I saw that yesterday and it was good.
I went to the websites that funfinder left and they also look good, especially the ground pioneer. WMD, what do you say to them? I ask because you certainly aren't afraid to say your opinions.
Though I tell you the (momentary) truth. If I could get a pre-loved tdi with a 1x1 coil, I probably wouldn't need much more. Maybe get a vlf to check for shallow discrimination if the tdi can't do it? If something sets off the 1x1 I'd probably want to dig it anyways, no matter what it is. 2 preloved units of vlf and tdi would probably come out to a better price than a new deepseeker unit from europe.
Hook that up to a data logger and it would be like a gun to a knife fight. Am I right in thinking that?
I see what you say Qiaozhi. I hope things are buried in an iron box or something. Maybe even if you didn't get a tone, a logger may still record it?
I apologize for being so green and ignorant, I thank everyone for being considerate.

[Funfinder]

Hi Qiaozhi,

this is interresting stuff and for shure there has to be some expotential
stronger power especially if mineralic ground weakens the field.

However there is some summing up in field distortion so individual coins
are detectable at much more depth at just one single of the same size.

My first test with canadian silver dollar one oz. and Jeohunter set to just 50%
sensitivity under strong nearby metallic and electro-smog living-room conditions
showed a distance of 20cm (8''). This coin is isolated in clear plastic.

Next i used 2 additional, a bit smaller and also isolated (paper) silver coins
with it so the total diameter of the "cache" was around 3inch / 8cm and 3mm thick.

In air the detection reached 30cm (almost 1 feet). Weight: below 100 grams.

But piling those 3 coins (isolated) gives still 20cm.


This is the proof there's more involved than just eddy currents of single coins:
the eddy current of one coin has induction effect to its neigbour coins even
if they're completly rusted or with patina as long as there remains a metal core.


The best detection of such 1kg cache will be if the coins be flat on the
ground / soil / hole and covering a large area like 10x10cm (4x4inch) or more.
And if I spread 1kg of coins over an even larger surface the depth may reach 4 feet.


That's why we first need a standard of the limiting size and shape.

[WM6]

WMD, what do you say to them? I ask because you certainly aren't afraid to say your opinions.

If WMD mean WM6, I can only say: "life is beautiful".

[Qiaozhi]

If WMD mean WM6, I can only say: "life is beautiful".

It means "Weapons of Mass Destruction"!
Oh ... perhaps that is you after all.

(Couldn't resist it.)

[joejoe]

If WMD mean WM6, I can only say: "life is beautiful".

It means "Weapons of Mass Destruction"!
Oh ... perhaps that is you after all.

(Couldn't resist it.)

Yeah, that was it. WM6. How could I get that mixed up? "life is beautiful"-Did anyone tell you that you are boring when you are nice? Just kidding, I respect your opinions. Do you still hate the jeofinder? From what I've read, it is not only you. I wish I could personally test one.
It's nice to see that people have a sense of humor. Makes the forum more fun.

[WM6]

Do you still hate the jeofinder? From what I've read, it is not only you.

There are no such fillings between me and Jeohunter. Simply Jeohunter is, what it is: impractical, High-OverPriced, "Hi-Tech" toy.

I only vote against promotion of useless things on Tech Forum in such way.

[mikebg]

MikeBG is referring to the fact that you need to increase the TX power by 64x to double the detection depth for a given object (e.g. a single coin). One twist on this idea would be to increase the target size by 64x. However, simply putting 64 identical coins in a pile will not work. This is because you do not have a 64x larger target, but a collection of 64 similar ones. Unless you electrically connect all the coins into a flat sheet, or melt them down to form one very large coin of the same thickness, the eddy currents will still flow in small circles within the individual coins, and there will be no doubling of detection depth. This is why the cache is harder to find than you might intuitively expect.

Qiaozhi, the increasing of TX power can not improve MD sensitivity even at air test.
My hobby was design of equipment for QRP amateur radio.
QRP principle is "maximize S/N ratio to minimize TX power".

When I tried to design a metal detector, I rediscovered that the S/N principle is generally not applicable to the conventional MDs because the RX sensitivity is not limited by thermal noise and EMI. When I increase TX power in order to increase the S/N ratio and the depth of detection, it turns out that the AIR & GND signal in RX input insreases and I am forced to decrease the gain of preamp to avoid its saturation. Low gain means decreased depth of detection.

Then I started to ask my hobby colleagues how to avoid this. Worldwide experts on radio communication formed a group for answering my questions. I reinveted method for increasing sensitivity of MD at air test without increasing TX power. Now remains to specify the method for improving target identification when it is buried in bad ground. Increasing TX power can not help also for this aim.

[simonbaker]

Qiaozhi, the increasing of TX power can not improve MD sensitivity even at air test.
My hobby was design of equipment for QRP amateur radio.
QRP principle is "maximize S/N ratio to minimize TX power".

When I tried to design a metal detector, I rediscovered that the S/N principle is generally not applicable to the conventional MDs because the RX sensitivity is not limited by thermal noise and EMI. When I increase TX power in order to increase the S/N ratio and the depth of detection, it turns out that the AIR & GND signal in RX input insreases and I am forced to decrease the gain of preamp to avoid its saturation. Low gain means decreased depth of detection.

Then I started to ask my hobby colleagues how to avoid this. Worldwide experts on radio communication formed a group for answering my questions. I reinveted method for increasing sensitivity of MD at air test without increasing TX power. Now remains to specify the method for improving target identification when it is buried in bad ground. Increasing TX power can not help also for this aim.

That does not make sense to me, at least for MD like TGSL (only one I'm familiar with).

I observe that dominant noise is EMI noise picked up by RX coil. I could be wrong, but that is what it seems so far.

That would imply that stronger TX signal should be able to overcome the EMI noise. Yes, you would need to reduce RX preamp gain -- and that is how you get greater S/N ratio.

I call "ground noise" the fluctuations in the ground that mimic targets. Stronger TX signal will not really help with that, I agree.

Regards,

-SB

[Funfinder]

@WM6
> There are no such fillings between me and Jeohunter. Simply Jeohunter is, what it is:
> impractical, High-OverPriced, "Hi-Tech" toy.
> I only vote against promotion of useless things on Tech Forum in such way.

And I vote against your childish games and view of things which has nothing
to do with real metal detector usage in rough practise!!!
Beeing an electronic-nerd and using MDs experienced are two different pair of boots!

And as long as guys like you don't understand what is fact and what counts while
spreading stupid opinions I have the right to defend reality if you like it or not, WM6.

[Funfinder]

Cache found with Jeohunter!

A few hours ago in the evening I reopened the hole where I found 2 months ago
that bucket-bottom almost 2 feet (55cm) below and extended it down to almost
70cm (2,1 feet).

Before I gathered selffound and other available coins so I got exactly 1kg.

I put them into a plastic bag and down the hole - diameter around 10cm
and 1-2cm thick.

First detection with open hole at sensitivity 80% was good.

After closing the hole with stones and sand I still found the cache
but at 90% sensitivity and the signal was smaller.

However - the coins-area just was around 12x8cm of size and if it would have
been possible to spread them more the detection would have been even better !

And because of the not so compact stones after closing the hole
compared to the surrounding area the Jeohunter had to compensate
this distortion into direction cavity, too.


If you don't believe that result get the Jeohunter or Jeoscan 2D with standard
45cm coil as example here http://www.metaldetector.cc and test it on your own.


btw. those results are almost the same as described at the general
search antenna table: 10x10cm object depth = around 75cm


Many details of this test with pix and movie you will find here soon:
http://www.geotech1.com/forums/showt...t=16374&page=9

[joejoe]

Has anyone else that has personally tried the jeo units say it is NOT true what funfinder is claiming?
One person said he personally tried the machine and it is a simple vlf in a fancy box. Will that person describe his experiences with it, pro's and cons?
I hear wm6's complaint about excessive promotion, and he may have a point, but I WOULD like to hear a detailed first hand experience that can go against what funfinder says.
If a two box can work similarly, is it unreasonable to think that these jeo units can also?
Of course, I do not have the technical know-how of you guys, so that is why I would like to hear your professional opinions of this technology. I find it invaluable.

[Funfinder]

Has anyone else that has personally tried the jeo units say it is NOT true what funfinder is claiming?
One person said he personally tried the machine and it is a simple vlf in a fancy box. Will that person describe his experiences with it, pro's and cons?
I hear wm6's complaint about excessive promotion, and he may have a point, but I WOULD like to hear a detailed first hand experience that can go against what funfinder says.
If a two box can work similarly, is it unreasonable to think that these jeo units can also?
Of course, I do not have the technical know-how of you guys, so that is why I would like to hear your professional opinions of this technology. I find it invaluable.

Have not much time now because I have to go to the buried coins:
joejoe, "fancy box" - what's this for an argument of such persons?
Completly untechnical - judging something because of colours and LCD display; btw you can see in the Jeohunter thread how this box looks inside - this is computer hitec! Did you read this thread completly or not?

And the arguments "overpriced", to heavy? Compared with the Nexus Ultima you get much more even for 3500 Euro. This is no mass-production, there is investment and further ongoing improvements involved.

And WM6's view those would be promotion is wrong - it started with pro-contra describtion - see first post! - and turned out to defending against stupid ridiculous claims. It's simply not fair against a company that is building and improving now for 25 !!! years metal detectors telling such sh*t about powerful machines and discriminating their satisfied users just by hearsay and because some short tests didn't mach up with the usually used "mini-coil" detectors.

If you want to built the best detector in the world with the most power and you work for 25 years on it you won't be happy if they start to compare cubes with balls! The Jeohunter plays in the Liga of 50cm and more frame coil PIs depth detectors and this has to be respected with all the special issues that occure in that category.

btw. two boxes do find only stuff that is 20cm (8inch) in size upwards and it's very uneconomical if you miss most of the targets just because those are smaller. The same with 1m PIs. It won't take long until you are frustrated if you're finding just very seldom some finds.

Have to leave now, in 1h it starts getting dark.