| How
deep can a good detector be expected to find coins? |
This
question is much easier to answer nowadays because virtually
all modern 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:
5p-10p
sized targets - 4 to 8 inches
2p-50p 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.
|
| 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 specialised types are less
adaptable to general purpose work. |
| Are
detectors with lots of knobs better than those with just a few
knobs? |
All
detectors fall into one of two classifications; 'turn on and
go' or 'do it yourself'. The first group have 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? |
An
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 extras. |
| What's
the difference between concentric and wide scan coils? |
A
concentric coil is better than a wide scan at discriminating,
but it is much more affected by the ground you are hunting.
A wide scan coil is less affected by the ground and it can be
a superior coil in areas of high mineral concentrations and
on salt water beaches. |
| Which
coil size is best? |
For
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? |
If
you 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, so
by eliminating pull-tabs, you are also eliminating all the
gold targets. Even if you use a notch discriminator to reject
pull-tabs, you will lose all those gold targets which have
the same phase response (or 'electronic fingerprint') as the
pull-tabs.
A
truly 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? |
Notch
discrimination can be used either to reject a narrow band
of targets (=notch reject), or to respond to a narrow band
of targets (= notch accept). It is usually used to reject
pull-tabs while still finding 5p and 10p coins and those gold
rings which 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.
If
the 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.
The
'notch 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? |
Yes
it 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.
Secondly,
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? |
First
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.
When
using 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? |
If
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 just disappears, you can tell what the
target is. All of this is done automatically and very rapidly
by a target ID detector as you swing the coil over each target.
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 artefacts 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? |
A
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 manual machine. |
| Are
battery test readings accurate? |
Only
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? |
Since
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? |
The
detection 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 magnetites, 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.
Early
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.
However,
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? |
Not
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 realise 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? |
Interference
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? |
They
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
search periods. |
| What
is ground cancelling, and how can I adjust my detector to the
right point? |
Think
of ground cancelling as being exactly the same thing as discrimination.
If your ground control is set too low (counter-clockwise)
the detector with 'reject' the ground. If your ground control
is set too high (clockwise) the detector will 'find' the ground
by beeping as the coil approaches the ground.
Your
aim 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 pull-tabs? |
Unfortunately,
most motion detectors can be fooled by large rusty items, especially
if those items are circular, 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? |
A
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
signals. |
| Is
depth sacrificed for accurate identification in a target ID
detector? |
Virtually
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? |
For
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 £500 detector better
than a £300 detector? |
The
£300 detector will probably have the same depth as the
£500 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 £300 detector. |
| What
is the best operating frequency for finding gold? |
Typically,
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. |
