How deep can good metal detectors be expected to find coins?
This question is much easier to answer nowadays because virtually all modern
metal detectors are 'motion' or VLF discriminator types. Most of them are also fitted,
as standard, with search coils of around 8" diameter, which is generally
regarded as the optimum size for coin hunting on sites with moderate amounts
of metallic litter. Using an incorrect sweep-speed will also affect depth, but
the following figures are achievable with a correctly used detector:
Nickel-Dime sized targets - 4 to 8 inches*
Quarter-Half Dollar sized targets - 6 to 12 inches*
Fruit jar lid sized targets - 8 to 16 inches*.
Many other factors can affect your detector's depth, but the same factors
will affect all other detector depths. The two most important things for
you to do today are to become familiar with your machine, and to use it at
the proper sweep-speed.
*Depths vary by model, manufacturer and coil size.
Can one detector 'do it all'?
Some of the better 'all purpose' detectors can make a pretty good job of most
treasure hunting assignments, but there are certain machines specifically designed
for such tasks as underwater work and gold nugget hunting. These specialized
types are less adaptable to general-purpose work.
Are detectors with lots of knobs better than those with just a few knobs?
fall into one of two classifications; 'turn on and go' or 'do it yourself'.
The first group has either a preset ground adjust, or an automatic ground
adjust. They do not require any further adjustment by the operator because
the electronic circuitry takes care of eliminating mineral effects. The
'do it yourself' group usually have a multi-turn ground adjust knob which
must be set to the correct position by the operator. Such machines are
generally capable of just a little more depth provided they are set correctly,
but they yield much poorer results when incorrectly adjusted. Both
'turn on and go' and 'do it yourself' units can be very effective.
What kind of detector should be used for [a] relic hunting and [b] coin hunting?
all-purpose detector will do both jobs, although a larger coil might be
an asset whilst relic hunting. For coin hunting, a motion discrimination
detector is virtually essential if you wish to avoid digging out every bit
of iron you find in the ground. Other features, such as notch discrimination,
target identification and coin depth indication can be regarded as optional
What's the difference between concentric and wide scan coils?
concentric coil is better than a wide scan coil at discriminating, but it is
much more affected by the soil you are working in. A wide scan coil is less
affected by the soil, and can yeild superior results in areas of high mineral
concentrations such as salt water beaches.
Which coil size is best?
an all purpose detector, the standard coil supplied with the unit is usually
the optimum size for most hunting. In extremely littered areas, a smaller
coil (4" or 7") will usually bring better results; even though
the smaller coil has less depth on coin-sized targets, your results will
be better because good targets are less likely to be masked out by bad targets
lying next to, or over them. When searching in relatively clean and litter
free areas, a larger coil (10.5" or 11") will usually yield better
depths and a wider area of coverage because masking of good targets is less
likely to be a problem.
How much discrimination should I use?
are serious about finding gold rings and gold coins, use as little discrimination
as possible. Most gold items are rejected at about the pull-tab level
of discrimination. By eliminating pull-tabs, you are also eliminating
most gold targets. Even when using a notch discriminator to reject
pull-tabs you may lose gold targets which have the same phase
response (or 'electronic fingerprint').
serious hunter, and one who has been successful over many years, will
have dug many pull-tabs, but that is why he has also found most of his
gold targets. With today's motion machines, it is pretty easy to get rid
of most of the iron objects, but those iron objects could be masking good
targets beneath them.
What is the purpose of notch discrimination?
discrimination can be used either to reject a narrow band of targets (a notch reject), or to respond to a narrow band of targets (a notch accept). It
is usually used to reject pull-tabs while still finding small coins
and gold target that do not have the same response as pull-tabs.
The notch level control generates a 'window signal' whose width is set
by a small component on the PC board. This 'notch window' can be moved
up and down the discrimination range until it properly covers the desired
range of target response.
detector is being used to eliminate the response to the pull-tabs, you
must remember that any good targets which have the same phase response
as pull-tabs, and which therefore fall within the same window, will also
be eliminated. Such good targets consist mainly of gold items and rings.
accept' feature can be used to tune the detector to a particular type
of item, such as a known type of ring. The detector will then only find
items which fall within that narrow notch window.
Does using notch discrimination cause loss of depth?
can cause a small loss of depth, for two reasons. Firstly, the notch discriminator
adds a slight amount of capacitance to the normal discriminating circuit,
and this slows the detector's response to targets. Sweep-speed then becomes
more critical when seeking deep targets, but if the detector is used at
the correct sweep-speed, the loss of depth will not amount to much.
Signal strength diminishes at the top and bottom edges of the notch window.
As the target approaches the response cut-off of the filters used, its
signal weakens. Setting the top and bottom edges of the notch window will
cause some loss of depth on those targets. However, a properly adjusted
notch window will not cause a great deal of depth loss.
How do I adjust the sensitivity control to get maximum depth?
find out which modes are affected by the sensitivity control on your detector.
Do it by turning your machine according to the instruction manual, and
then waving a good target over the coil with the sensitivity control set
first at the maximum, then at the minimum position. If the detecting distance
alters, then the sensitivity control is functioning.
the detector on site, set the sensitivity control as high as ground conditions
will allow you to use the machine without too many false signals or spluttering
noises. Too many spurious signals will make hearing the weak responses
of good, but deep targets difficult.
How does target ID work?
you have any kind of discriminating metal detector, you already own a 'do
it yourself' ID machine. By increasing the discriminate level until the
target disappears, you can tell what the target is. This is done
automatically and very rapidly by a target ID detector while you work. Basically, the electronics measure the phase
angle of the target at the moment the signal occurs. It generally takes
only one pass over the target to get accurate identification, although the
earliest models required several swings, which is why they were know as
'pump up' ID detectors. However, on older sites, many ancient coins and
artifacts may show as junk or reject signals. ID detectors therefore are
best suited to searching for modern coins.
Is manual ground adjust better than fixed ground adjust?
fixed or automatic (ie factory preset) detector will always give good performance,
no matter what type of ground you are hunting on. A manually adjusted machine
may increase the detection depth by a small amount, but only if the adjustment
is very accurately carried out. Incorrect adjustments may give horrendous
results. For the average user, a preset or automatic detector's performance
is superior to the results that might be obtained with an improperly adjusted
Are battery test readings accurate?
if the tests are done while the batteries are delivering the proper amount
of current to the detector. Some cheap battery testers, and even some more
expensive meters, may give erroneous results when used to test batteries
that are not delivering current during the test. An audio test is much more
reliable since the audio circuitry loads the battery to the detector's full
power while the test takes place.
By how much will the use of headphones increase battery life?
the speakers in most detectors are of 8 or 16 ohms impedance, while most
detectors use a resistor of approximately 100 to 200 ohms to limit the sound
output in the headphones, the current necessary to drive a set of headphones
is considerably smaller than that required to drive the low impedance speaker.
Using the figures just given, a set of headphones would increase battery
life by 2 or 3 times. However, since the electronic circuitry in the detector
is always operating when the machine is switched on, even though the detector
may not be making any noises, the savings on battery life may not be as
big as the above numbers seem to indicate.
Why does my detector sometimes detect rocks and tree roots?
of rocks can be due either to your detector's ground adjust not being
set correctly so that typical 'hot rocks' are ignored, or to the rock
that you have just found being a truly positive reading mineral sample.
Hot rocks are iron ores or magnetite, which are 'negative' with respect
to normal ground signals. Their intensities can vary considerably, which
makes setting the detector to get rid of all of them a little tricky.
motion detectors usually 'beeped' at hot rocks, but switching to all metal
yielded a 'null' response. Since the hot rock was negative in all metal
and also negative in discriminate, both signals were the same, and the
detector said 'good target' even though it was really bad. Today, most
manufacturers set the ground adjust so that the filtered all metal signal
responds in a positive fashion to hot rocks. Therefore, the signals are
different, so the detector doesn't beep at negative hot rocks.
minerals come in many different forms, and some of them are detectable.
Tree roots can also absorb various chemicals and end up being electrically
conductive. Sometimes, all you can do is grin and bear it.
Will meter detectors find coins deeper than non-meter detectors?
generally. It takes some kind of circuitry to drive the meter, and if that
circuitry has more gain than that which drives the speaker, it may be possible
to detect deeper with the meter. But virtually all manufacturers realize
that if they can get deeper performance, they will add the extra gain to
the audio stage as well.
How do I overcome interference from other detectors when I am at a rally?
occurs when two detectors of similar frequencies operate in close proximity.
The nearer the frequencies, the further apart the two detectors will interact.
Crystal controlled detectors are especially prone to this problem because
the crystals are very accurate. The only solution in that case is to fit
a 'frequency shifter box' or to get further away from the interfering machine.
Are 'audio enchanters' any good?
operate by amplifying weak signals and attenuating strong signals. Thus,
they tend to make all signals sound alike. They can be helpful when you
are hunting in TR discriminate, or in all metal mode, or if your detector
has an 'audio threshold'. However, on 'silent search' detectors are less
effective, though they do limit the sound in your headphones when you pass
over a piece of surface junk. This can add to your comfort during extended
What is ground canceling, and how can I adjust my detector to the right point?
of ground canceling as being exactly the same thing as discrimination.
If your ground control is set too low (counter-clockwise) the detector
will 'reject' the ground. If your ground control is set too high (clockwise)
the detector will 'find' the ground by beeping as the coil approaches
is to set the ground control so that the detector remains neutral to the
ground, or doesn't see the ground at all. It will then detect as deep
in the ground as it does in the air. To accomplish this, first tune the
detector to a threshold tone while holding the coil in the air. Then lower
the coil to the ground and listen. If the threshold dies away, turn the
ground control in a clockwise direction. If the threshold tone gets very
loud, turn the ground control counter-clockwise. Next, raise the coil,
retune to a threshold tone and repeat the above operations. When you get
it right, the sound will change very little as you lower the coil.
Why does my detector find large deep nails and rusty iron even when set to reject
most motion detectors can be fooled by large rusty items, This is especially true of circular targets, such as iron washers and steel bottle caps. Sweeping
the detector faster will help a lot on the steel bottle caps, and it will
help some on the washers. Fortunately, large pieces of iron will be heard
as much 'broader sounding' targets than non ferrous items in the all metal
mode. Experienced motion detector users rarely dig large pieces of iron.
Does the moistness of the soil affect detection depths?
lot of metallic targets corrode when lying in damp soil. This can cause
the target to appear much larger than it really is. When the soil dries
out, the corrosion may not affect the detector and the target will seem
more like its normal size. Gold doesn't corrode in the ground, and silver
doesn't corrode nearly as much as copper, brass and bronze. Iron and steel,
of course, rust in moist ground, and can cause some really horrendous false
Is depth sacrificed for accurate identification in a target ID detector?
all target ID detectors can find targets much deeper than they can identify
them. Discrimination only requires one reference signal, which yields a
positive signal for good targets and a negative one for bad targets. To
identify the target requires some very special and complex electronic circuitry,
which does not have the ability to reach the same depth as a simple discriminator.
If manufacturers limited the depth of their ID machines to the depth of
the identifier circuit, they would sell a lot fewer detectors.
How should I adjust the discriminate level on my detector to achieve maximum depth?
maximum depth, set the discrimination level as low as possible. To get the
absolutely best depth, set the discrimination level at the point where you
get a broken signal, rather than no signal at all, from the type of object
you want to reject. This will give you some additional signal on all good
targets that are heard.
By how much, and in what ways, is a $1000.00 detector better than a $600.00 detector?
$600.00 detector will probably have the same depth as the $1000.00
machine, but it will not have all the features of the more expensive unit,
such as a meter, depth measuring ability, notch capability, target ID, multiple
discriminate levels, surface blanking, and the other 'bells and whistles'
that can raise the cost of a basic machine. But unless you really want those
features, and understand that you will consume a lot more batteries by powering
them, why pay for them? Although some manufacturers may put less gain in
their cheaper models, you should expect to find only fewer features on your
What is the best operating frequency for finding gold?
most VLF detectors, made today operate in the 5 to 15kHz range, while gold
detectors typically operate at about 20 kHz. The increase in frequency gives
a minutely greater response to tiny bits of gold, but the increased response
to small targets results from them having about ten times as much gain as
general purpose detectors. Increasing the frequency much above 20kHz gives
a tiny bit more response in air tests, but the increase is lost as soon
as the target is laid on the ground.