What is the deepest metal detector
How deep will a metal detector go
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How deep can a metal detector can penetrate the soil
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How deep can a metal detector find treasure
The buried hoard test : I wanted to know how deep a discriminating metal detector could detect a small hoard, so was told to go and get some machines, a big spade and some coins.
These days we hear so many stories about new models going deeper than ever before, we read about people finding coins and artefacts over 2 feet in depth.
I have always been interested in finding a small hoard at 2 feet is it scientifically impossible using the metal detectors we are all searching with today, I have been told coins with a patina are electronically isolated from one another so in the ground a detector will not see the coins as a mass, more like several individual targets.
Note :
We can only test metal detectors available at the time
We are not interested in testing a machine with no discrimination circuit as you would not search in all metal on a junky ancient site.
Also this test is to simulate coins buried in a non metallic container which has almost certainly been destroyed, eg: leather pouch, clay pot, wicker basket wooden box.

We decided to carry out 2 tests in my garden
Test A to bury a sixpence at 10 inches deep
Test B to bury a small hoard of coins 1kg at 25" just over 2ft...64 cm to be exact
Both underneath undisturbed soil or as close as we could simulate.

The Test
We dug the hole to 70 cm then burrowed 2 channels into the opposite side walls 8-10" long
One at 64 cm deep marked "B" the other at 10" deep marked "A" .
This was to ensure the targets were placed underneath mostly undisturbed soil.

hoard test diagram
The test diagram
Our earlier tests had proved that the Halo effect of buried coins etc played no real part in detection depth in fact the halo effect only applies to Iron. To prove this fact next time you dig an ancient coin try to detect the soil in which it came out, if the halo effect was true the soil would give off a signal to.
The silver sixpence was placed in pod "A" the 1kg coin hoard was in pod "B" (see diagram).

Machines used
Minelabs : Explorer with standard coil, Sovereign with WOT coil, Quattro standard coil
Gold Maxx Mk1
Whites, XLT, MXT
Nexus, std coil, prototype coil
Tejon with big coil and standard coil

The Digging starts
the hole in my garden
The test hole
It is surprising how hard it was to dig this deep....
bloody deep hole deep enough to bury a Bulgarian Hmmmm test hole 67 cm deep
I can't get my head around Centimetres let's try inches

Measurements in inches and centimetres
the test hole at 26" deep

The control a highly conductive Aluminium test piece

our first test
Before we carried out the full test we buried a highly conductive aluminium piece at the bottom of the hole and the filled it in with the earth and packed it down hard.. Only 3 machines picked this target up with a faint signal through the disturbed soil. The Minelabs, Tejon (Big coil), Nexus with std 9" coils.
Loose earth in a freshly dug hole is not a fair test for a machines depth capabilities, all machines tested would indeed pick the hole up as part of the target giving a false depth impression.

Then we dug the hole out and placed the aluminium piece in the side pod "B" and filled the hole again, now we could test it under undisturbed soil.

deep hole
The side pocket "B" is next to the screwdriver
  high conductivity sample hoard test diagram
the aluminium test target

Test Result:
Only one machine could detect the Aluminium target beneath the undisturbed soil.
At 25" deep the Nexus with the 12" coils was the only machine that produced a smooth signal on the large Aluminium.

Now it is time to bury the simulated hoard underneath un disturbed soil...Pocket B
* Note there is still quite a lot of small nails and small iron surrounding the hoard to simulate real detecting conditions.

the buried hoard test Copper and silver coins
Coins located in the side of the hole

1KG of mixed copper and silver coins some with the original soil still stuck to them, the coins were placed in pocket "B" and the hole was filled in.

Ready for the test......One ruined garden
A buried hoard of coins for a metal detector to find

Test results
You would have expected the Nexus to pass this test with flying colours but it failed with all the other machines.
So beware of sellers claiming their machine is the deepest hand held detector in the world or words to that effect, there are to many different scenarios to take into account ...it is probably just a get rich quick scam.

The test is now in place for ever, it will be interesting to test new machines in the future.
Next time someone says they dug a hammered coin at nearly 2 feet simply give them a tape measure and a link to this page.

Targets can be possibly be detected this deep providing they are
A: Bigger in mass than our test coins
B: Higher in conductivity than the targets used.
Most Pulse machines and pipe locators up to date have no discrimination (so not a fair test) I will post results if and when I get one that discriminates iron.

This myth is Busted
Can machines that don't air test well, go deeper in the soil ?
No absolute Crap !! this is scientifically impossible if a machine air tests badly it will detect badly in the soil despite what you read on metal detecting forums and some manufacturers literature.
However some machines that air test better can loose a higher percentage of depth in the soil around 30% depending on what type of search coil is used.
If you suspect these results are wrong, please go out there and do the buried coins test for yourself.
I think you will be amazed!!!!.

Letter from reader
Hi Gary,
How refreshing to see the results of your hoard testing.
I have done a number of tests myself admitted not to the depths you went .
Here is one:-
I super glued a 12mm dia roman bronze it was approx 1mm thick on the end of
a 3" piece of 1" dia dowel rod and pushed it into the ground so the ground
was relatively undisturbed,  now this coin had been checked "in air" with the
(2)-----Sov gt with 8" coil------8".
(3)---- xterra 50 7.5khz coil---9.5".
(4)----xp goldmax----6".

 Result NOT ONE machine gave a diggable signal.
Only the Cibola gave any indication there might be a target lurking below the surface. As for the claims that some machines will detect a target at a
greater distance in the ground than in the air is as you put it absolute crap.
My conclusions to this type of testing is that if you take all the machines from the top brand manufacturers the results in the ground are to a degree very similar with one another and the only real differences
are the likes and dislikes of the operator, mostly concerning the weight, sounds and ergonomics of individual machines. As for the claims made on ebay
from some sellers of detectors it is truly laughable well it would be if it wasn't so dishonest.
Anyway Gary  love your site
Kind regards,

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