In order to serve you
more promptly, we are taking the liberty or replying
to your letter with a standard form containing answers
to FAQS (frequently asked questions). Should you find
it necessary to write again, please include your original
Brennan, Ste. H
El Paso, TX 79936
TEL (915) 225-0333, FAX (915) 225-0336
How deep will a metal detector/locator go? [top]
A: This is the question
most frequently asked. Unfortunately, it has no absolute
answers. The following variables, in addition to your
own detector's capabilities, all have an effect on
1. Conductive properties
of the soil: Heavily mineralized soil will tend to
reduce the penetration power of your detector. Soil
mineralization may vary greatly, and you may have
to re-ground balance your detector to adjust for soil
mineralization; unless, of course, your detector has
automatic ground balancing. In this case, you may
need to decrease sensitivity and/or increase discrimination
on models like the Fisher 1266-X, which has extraordinary
2. The length of time
an object is buried: Various chemicals in the soil
have a corrosive action on metal. Some metals corrode
faster than others. A modern zinc penny is attacked
by these soil chemicals quite easily, whereas the
action on copper and silver is much less, and corrosive
action on gold is hardly noticeable, if at all. As
these chemicals eat away at the metal, oxidation (rust)
takes place, which is absorbed into the surrounding
soil. This causes the soil to become more conductive,
which in turn makes the metallic object appear larger
than it actually is and easier to detect. This is
known as the "halo effect."
3. The size of an object:
The larger the metallic object, the easier and deeper
it can be detected. For example, a bucket can be detected
much easier than a single coin. The more surface area
seen from above, the deeper the metallic object will
4. The shape of an object:
Every metallic object reradiates at least part of
the signal transmitted by your metal detector. In
this way, objects function like additional antennas,
and consequently their shape becomes important. Ring
or loop-shaped objects lying flat, on or under the
ground, produce the best results; flat or dish-shaped
objects are similarly easy to detect. Rod-shaped items,
especially when scanned end-on, are very difficult
to detect unless they're made of iron and you're using
a ferromagnetic detector, such as the Fisher FX-3.
5. The degree of magnetization:
With ferromagnetic locators, such as the FX-3, the
degree of magnetization has a strong influence on
depth. A magnet, for example, can be detected at much
greater depth than an equivalent mass of iron. The
more magnetization an object has, the deeper it can
be sensed by a ferromagnetic metal detector.
Regarding the size of search coils, is bigger better?
A: Several coil sizes
are usually offered for each detector. Each size offers
specific strengths and weaknesses. A small coil is
better than a larger coil for picking out good targets
among many trash targets. The standard, 8-inch coil
is an all-purpose coil. It is the most popular coil
size, and it performs well under most conditions.
Larger coils are best suited for low-trash and low-mineralization
areas. They cover more ground and increase depth penetration
5-15 percent. However, larger coils are heavier, and
some detector users feel more comfortable during long
searches if they use a smaller coil. Having more than
one coil size is often helpful for varying conditions
you will encounter. Elliptical coils, which get into
nooks and crannies easier, are also available. All
Gold Bug and Gold Bug-2 coils are elliptical in shape
and measure 6 1/2, 10 and 14 inches in length. A 10-inch
elliptical coil is also available for the 1200-X series
Fisher detectors. Although it offers slightly less
depth penetration, its lighter weight makes it the
favorite of Treasure Hunters who attend competition
A: A better word for
discriminator is perhaps "differentiator."
At minimum or no discrimination, all metal within
the detectable range is detected. As you slowly increase
discrimination, small pieces of metallic trash and
ground mineralization are ignored (rejected). As you
increase the discrimination, pull tabs, small nails,
foil, and even some good targets (such as gold rings
and nickels) will be rejected. The best way to learn
the discrimination points (the lowest discrimination
setting at which an object is rejected) of your detector
is to scatter some sample targets, such as coins,
pull tabs, and foil on the ground from 1-2 feet apart.
Starting at 0, or your detector's lowest discrimination
point, scan each target. Gradually increase discrimination
and record the results. With practice, you should
be able to determine whether or not to dig by listening
closely to the target signals.
The Fisher Gemini-3 and
TW-6 "two-box" metal detectors can locate
large metallic objects at great depthsobjects like
pipes, cables and treasure caches. These "two-box"
detectors consist of a signal-receiver box and a signal-transmitter
box connected by a handle.
What is the sensitivity control and how is it used?
A: The sensitivity control
on metal detectors is probably the most misunderstood
control on the instrument. Sensitivity is usually
set to its maximum level and ignored. This does not
always allow for maximum operation of the detector.
To use an analogy, think of the sensitivity control
as the throttle of a car. You don't drive everywhere
at full speed. In fact, posted speed limits are for
normal conditions. But what about rain, snow, or even
high wind? Of course, you decrease your speed. Likewise,
you should adjust your sensitivity control for varying
conditions. Heavy ground mineralization, nearby power
transformers, and nearby radio stations are all reasons
to lower your sensitivity. Although you might experience
a slight loss of depth, you may be losing more good
targets than you think by listening to the false signals
and chatter of high sensitivity.
Why do serious metal detectorists use headphones?
A: Headphones can greatly
reduce outside noise (wind, waves, traffic, etc.).
They also enhance the audio target signal, which will
help you determine which targets to dig and which
targets to ignore. Overall, a good set of headphones
will improve the number of your good finds and greatly
reduce the time you spend digging trash. Headphones
also reduce distractions, extend battery life and
keep you from attracting unwanted attention from curious
onlookers. Fisher offers two different headphone models:
one standard set and specially designed Fisher Phones
that give Fisher detectors superior performance. Acoustically
designed for faint-target response, Fisher Phones
make faint, deep target signals easier to hear. No
additional batteries are required for these headphones.
A: False signals are
sometimes called "phantom" signals. They
occur any time your detector responds to metal when
there is actually no metal there. False signals are
most often caused by naturally occurring iron oxides,
such as magnetite and hematite. Magnetite is the primary
constituent of the "black sand" that commonly
occurs in placer gold deposits. Most Fisher models
have automatic ground balancing to accommodate without
a false signal but the most severe deposits of mineralization.
If your detector has a manual ground-balance adjustment,
you can usually tune out false signals. Sometimes
you may need to ground tune frequently if the mineralization
of the soil changes abruptly as you move from one
place to another. If ground mineralization is excessive,
turning down your detector's sensitivity may be the
Which detector is best for finding large, deep targets?
A: A "two-box"
detector, such as the Fisher Gemini-3 or TW-6, is
best for finding large, deep targets, such as caches
(hidden treasure troves) or buried pipes and cables.
But using a "two-box" detector on a connecting
handle is different from using a standard, hand-held
metal detector. Although it goes deeper, the smallest
metallic object you can hope to find with a "two-box"
detector is about the size of a cantaloupe melon,
even if the melon-sized object is resting on top of
the ground. However, that same melon-sized object
may be detected at a depth of up to 6 feet with a
Fisher Gemini-3 or TW-6. Maximum depth with these
"two-box" detectors is achieved by carrying
the unit low to the ground, suspended by a strap.
An extra-long handle is available for the Gemini-3
and TW-6 that also increases depth penetration by
widening the separation of the boxes on the handle. Q:
Are metal detectors safe for people with pacemakers?
The question of whether
pacemakers present a safety issue in relation to metal
detectors is one which we have paid close attention
to over the years. We are not aware of any report
of a hobby type metal detector ever interfering with
a pacemaker or other electronic medical device, or
having any other adverse health effect.
The magnetic field to
which a hobby metal detector exposes the user in normal
use is much weaker than the geomagnetic field which
already surrounds us, many times weaker than the electromagnetic
radio waves near a broadcast transmitter or CB radio
or cellphone, and weaker than the magnetic field of
walkthrough security metal detectors such as are used
in airports and courtrooms.
Because hundreds of millions
of people each year are exposed to the field of walkthrough
metal detectors, government agencies involved in security
have conducted a lot of research into the potential
for interference with pacemakers. Over the years there
have been perhaps one or two reports of a brief malfunction
which resulted in no serious harm to the “searchee”.
Because there can be no absolute guarantee that there
will be no such interaction, it is customary for security
to post a notice where walkthroughs are being used,
advising “searchees” who are wearing or
who have implanted electronic medical devices that
they may be hand searched without going through the
The manufacturers of
pacemakers design them to be resistant to interference
from electromagnetic fields. An obvious concern to
manufacturers of pacemakers and other implantable
and wearable electronic medical devices is fields
from walkthough security metal detectors. Pacemakers
and most other electronic medical therapy devices
require FDA approval, and reliability and safety are
criteria which must be met in order to receive that
approval. However the bottom line is that we have
no control over how pacemakers are designed and manufactured
and therefore can make no absolute guarantee what
they will or will not do.
The magnetic field of
a hobby type metal detector is concentrated within
a few inches of the searchcoil. It is probable that
most medical devices would continue to function properly
with the searchcoil brought up next to them. If there
were a malfunction it is unlikely that there would
be any damage: normal operation would likely resume
once the searchcoil was moved away from the device.
Despite all that, common sense would dictate that
a person with an implantable or wearable electronic
medical therapy device should not bring the searchcoil
up next to the device. This of course is not something
that a person would normally do anyhow.
Chief Designer, First Texas Products and Fisher Research