Whites TDI BeachHunter User manual

Owner’s Manual
TDI
BeachHunter
White’s Electronics, Inc.
Sweet Home, Oregon USA
Building the World’s Finest
metal detectors for over 60 years.

2
CONTENTS
Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Batteries and Charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
QuickStart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Principles of Pulse Induction . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Controls
Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Power/gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pulse Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Target Conductivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Ground Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
TDI In Depth
Ground Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Audio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Pulse Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Dual-eld coil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Dealing with Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Code of Ethics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Back Cover

3
Cam lock
Clevis
Rubber washers (2), ber bolt
Search coil
Lower rod
Arm cup
Battery door
1. Remove all parts from the shipping carton and check assembly
diagram to ensure all parts are present.
2. Install black rubber washers on ber clevis/lower rod, insert
clevis lower rod onto loop ears. Use only nonmetallic wash-
ers, ber bolt, and ber thumb nut to secure loop/search coil
to clevis/lower ber rod.
3. Unlock middle rod cam-lock and insert clevis/lower rod into
middle rod so that stainless steel spring clip buttons line up
and lock into one of the adjustment holes in the rod. Turn
cam-lock to secure. The second or third adjustment holes are
suitable for average sized adults.
4. Wind the loop cable around the rod assembly, rst revolution
over the top of the rod, all the way to the top of the middle
rod, about ve revolutions. Use the black cable retainers, one
near the loop, and one near the top of the middle rod, to hold
the loop cable in place. Make sure the cable is wrapped all
the way to the front of the control box.
5. Grip the instrument by the handle, with your arm in the
elbow cup with strap and sweep the loop/search coil over
Assembly

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the oor. If the instrument t feels uncomfortable, readjust
clevis/lower rod length with spring clip button and cam-lock
so that search coil can be held near the oor without stooping
over.
6. Remove the protective paper from the two black arm cup
foam pads. Carefully align pads on the inside of the elbow
cup, one on each side of the center rod, and press rmly into
place.
7. Adjust the elbow cup strap so that it is loose enough for you to
slide your arm in and out without loosening each time you
want to set the detector down. The elbow cup strap provides
extra leverage and control. However, some prefer not to use
it.
8. Install the battery pack; see the next section for information
on batteries and charging.

5
Batteries and Charger
The TDI-BH includes a rechargeable NiMH battery pack as
the primary power source, and a standard alkaline battery pack
as a backup. Fully charged, they supply a nominal 12 volts (the
NiMH may be slightly less) and will power the TDI-BH for
about 4-6 hours. The TDI will operate until the batteries drop
to about 8.5 volts, at which point the low battery LED will turn
on.
A drop-in charging cradle (Part Number 509-0036) is used
for recharging the NiMH battery. With the wall transformer
connected to the cradle and plugged into a wall socket, simply
drop the NiMH pack into the cradle. An LED indicates the
status of the charge cycle; when the LED turns off, the charge
cycle is complete and the charger will automatically switch to
a trickle mode. A typical recharge time of a depleted NiMH
pack is 1-2 hours. It is normal for NiMH batteries in storage to
slowly lose their charge over time; be sure to top off them off
before going out.
The alkaline pack is designed so that it cannot be used with
the charger, and trying to recharge alkaline batteries can cause
them to burst and leak. Individual NiMH batteries can be used
in the alkaline tray; it is recommended that the batteries be re-
moved and charged using the manufacturer’s charging system.

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QuickStart
1. Ensure machine is adjusted for comfortable t and use.
2. Set the Frequency offset to the midpoint.
3. Set the Ground Balance to 6-8.
4. Turn on the power and adjust the Gain to “2.”
5. Adjust the Threshold and Volume to achieve a faint back
ground hum.
6. With the coil on the ground (no motion) increase the Gain
until the audio begins to chatter. Back off slightly for a
reasonably smooth threshold.
7. Optional: adjust the Frequency offset to minimize the amount
of chatter.
8. Using a spot free of targets, bob the coil up & down and
adjust the Ground Balance control to minimize the audio
response.
9. In heavy salt or mineralization it may be necessary to adjust
the Pulse Delay to around 15-20us.

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TX
RX
Exponential decay
No target
Raw Response
The Pulse Delay control, which determines the point where
the decay is sampled, can be used to eliminate low conductive
targets such as thin foil. Further increasing the delay can knock
The use of high-powered impulses results in better ground
penetration than VLF, especially in highly mineralized soil. This
makes the PI detector the best choice for certain kinds of hunting
in bad ground where many VLFs simply won’t work.
There is no traditional discriminator in PI detectors, although
there is some ability to discern certain types of metals. The decay
response varies with target conductivity (plus other characteris-
tics) so that low conductive targets have a fast decay and high
conductive targets have a slow decay:
Low-conductive target, fast decay
High-conductive target, long
decay
Principles of Pulse Induction
Pulse induction (PI) detectors are very different from tradi-
tional induction-balance (VLF) designs. Instead of transmitting
a continuous-wave magnetic eld, the PI detector periodically
transmits brief impulses of magnetic energy. The PI receiver
then looks at the impulse decay for target (and ground) infor-
mation.
Pulse Rate

8
out other minor trash targets at the expense of eliminating po-
tentially good targets such as jewelry, but this method is very
limited in the range of trash targets that are rejected.
Furthermore, the ground balancing method used by TDI has
a side affect with target responses. Target conductivities below
the ground balance point produce a positive response for which
TDI assigns a high tone. These targets are generally low con-
ductive such as small nuggets, jewelry, and small iron. Target
conductivities above the ground balance point produce a nega-
tive response for which TDI assigns a low tone. These targets are
generally high conductive such as silver coins, relics, and large
iron.
Low-conductive target
No target
High-conductive target
Ground balance point
Differential Response
The Target Conductivity switch can be used to eliminate either
class of targets, or to accept them all. Care should be used with
this feature as it is not always obvious as to how a target might
respond. Testing with known targets is the best way to learn the
responses.

9
Controls
Threshold
The Threshold control sets the level
at which the background audio tone is
heard. In most cases, faint target signals
are easiest to hear when the threshold is
set to a low but clearly audible level. A
higher threshold level can result in audio
fatigue. Too low of a threshold level
means that a stronger target signal is
required to produce an audible change. Threshold is best deter-
mined at a low gain setting where there is no chatter.
The threshold can be set low enough to effect a “silent
search” audio. Some people prefer silent search to prevent audio
fatigue. If you choose to do this, increase the threshold to the
point where you can hear the threshold tone, then slowly back
off until it is barely inaudible. Reducing the threshold any more
than necessary requires stronger target signals to produce an
audio response. Other controls — including Gain, Ground Bal-
ance, and Frequency offset — are best adjusted with an audible
threshold.
Power/Gain
The Gain control increases or decreases the amplication of
the receive signal. Normally, this deter-
mines how deep the detector will “see”
a target.
However, increasing the gain not
only increases the amplication of tar-
get signals, but also that of ground
signals and electromagnetic interference
(EMI) as well. A common mistake is to
assume

10
that higher gain will always give better depth. In air tests this is
generally true, but ground results can depend on the amount and
type of mineralization.
With the coil on the ground, increase the gain until the
detector exhibits chatter, then back off slightly for a reasonably
steady threshold tone. Use the Frequency offset control to help
deal with EMI-related chatter, and proper ground balancing will
minimize chatter due to mineralization.
The Gain control is also used to turn the detector on and off.
Pulse Delay
TDI transmits a pulse and then, after
a short time delay, samples the received
signal. Pulse Delay allows this time
delay to be adjusted from 10μs (micro-
seconds) to 25μs.
In response to a transmitted impulse,
all targets exhibit a response
with an exponential decay. Regardless of
conductivity, the response is strongest at low sample delays and
weaker at higher delays. However, targets of low conductivity
or that are thin will decay faster than highly conductive or thick
targets. See the Principles of Pulse Induction section for more
details.
Smaller gold nuggets fall in the former category, so nugget
hunters will want the Pulse Delay set as low as possible. Coin or
relic hunters may want to increase the delay to knock out thin
foil trash and still detect desirable targets. Most iron (especially
larger) responds with a long decay and is usually not very re-
sponsive to the delay setting.
Conductive salts also respond with a fast decay and can be
detected at low delay settings. If beach hunting in wet salt sand,
you may need to turn the delay up to 15μs to eliminate the salt
response. Dry salt is usually not a problem, so as you move out
of the wet sand into dry sand remember to turn the delay back
down to better detect small jewelry items.

11
Pulse Delay affects the ground balance point, so whenever
the delay is changed the ground balance should also be checked
and re-adjusted. Higher pulse delays require a lower ground
balance setting.
Target Conductivity
Target Conductivity refers to the reactance of the target either
above or below the ground balance point of the TDI. General-
ly-speaking, gold is considered to be a low conductor (high tone)
and silver a high conductor (low tone). Iron often produces a
confused, warbly pitch that jumps back and forth between high
and low tones. The two-tone response is disabled when ground
balance knob is turned to the OFF position.
Be aware that target conductivities can vary considerably,
even targets of the same metal. Small gold nuggets are usually
low and large gold nuggets are usually high, but where the tran-
sition occurs depends on the composition of the gold alloy. Be
mindful that searching in low-conductivity mode could eliminate
very large nuggets, if any happen to be in the area1.
The same is true for relics and jewelry. Many bullets, but-
tons, and most buckles register as high conductors, but cuff
buttons often respond as low conductors. Most small jewelry
responds as low conductors, but larger men’s rings can easily fall
in the high-conductive range. Most coins fall in the high range,
except for e.g. US nickels and small or thin coins like hammered
silvers or very small bronze coins.
1. The potential for Very Large Nuggets depends on where you are
detecting. In most gold-bearing regions of the US, detectable
gold is found as small placer nuggets up to multiple grams in size
which register as low conductive targets. Alaskan and Australian
gold is still being found in multiple ounce-sized nuggets, which
may respond as a high conductive target.

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Ground Balance
This control is used to balance out
the signal from ground mineralization.
There is an OFF position for which TDI
runs in straight PI mode with no ground
balance.
To ground balance TDI for optimum
performance in ground conditions per-
form the following steps. Set the Gain
to about the mid-point or until the audio just begins to chatter.
Pump the search coil up and down from about one inch off the
ground up to 6-8 inches above the ground while listening for a
change in the audio. If the GB is too low, the audio will have a
high tone when the coil is lowered to the ground; if the GB is too
high, the audio will have a low tone. Adjust the Ground Balance
control for minimal audio changes. For most moderate mineral-
ization, this will be around “7-8”. A simple technique is to start
with the GB set intentionally too low (say, 5), then pump the coil
and increase the GB until the high tone begins to transition to a
low tone.
If the Pulse Delay control is changed, you will probably need
to re-adjust the Ground Balance setting. In addition, if you begin
to hear ground noises (false signals) as you sweep the coil you
should check the ground balance.
There are some cases where a particular target will fall exact-
ly on top of the ground balance point and TDI will not be able to
detect it at all. Targets that are close to the ground balance point
may have their response shifted if the Ground Balance control is
adjusted. For example, a given target may have a low conductor
response with GB=9 but a high conductor response at GB=5.
Turning the Ground Balance to the OFF position disables
the ground balance and TDI will run as a straight PI detector.
This gives a slight improvement in responses to targets that fall
right under the perfect ground balance setting, but the TDI will
respond to mineralization and it eliminates the ability to discern
conductivities.

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Frequency
This control makes small adjust-
ments to the transmitter pulse rate. This
is used to counteract any interference
which might be due to outside elec-
tro-magnetic sources, such as radio
stations, microwave, short wave, electric
fences, power lines, lightening, electri-
cal storms, or other metal detectors be-
ing used nearby. This interference is recognized by a warbling
or repetitive pulsing of the audio threshold, and can mask target
signals.
If you are experiencing interference, adjust the Frequency
control for minimal chatter. Adjustments should be done in
small steps, with a few seconds between each adjustment to see
if the TDI settles down. If you cannot deal with interference with
the Frequency control, then reduce the Gain and/or Threshold
settings to obtain a reasonably stable operating point.

14
TDI In Depth
Ground Balancing
One of the key features of TDI is its ability to balance
out ground mineralization while maintaining pulse induction
depths. This is achieved using a differential technique whereby
two decay samples are compared; the Ground Balance control
is adjusted until the two samples have the same response, there-
by canceling the ground signal.
Targets below the GB point produce an overall positive
response, and targets above the GB point produce an overall
negative response. Broadly, the two ranges of targets depend
on conductivity, which gives TDI some ability to discriminate.
In rare cases a target might fall so close to the GB point that it
gives either no response at all or a double-tone response.
Because ground balance is achieved using a subtraction
method, there is a slight loss of depth any time ground balance
is on. Some ground, notably neutral beach sand, is mild enough
that no ground balance is needed. In such cases, Ground Bal-
ance can be switched off and TDI will run in straight PI mode.
This will slightly improve depth, but loses the ability to distin-
guish between low and high conductivity targets.
Audio
TDI has the following audio tonal responses:
Ground
Balance
Audio Tones
Low
Conductor
High
Conductor
On High Low
Off High High

15
Low-conductor
Noise
Target Conductivity = ALL
Ideal no-noise
High-conductor
With Ground Balance = On, all targets will give an audio re-
sponse, either a high or low tone. New users are encouraged
to use this setup and practice with various targets to learn their
audio responses. A US nickel or small gold nugget works well
for a low conductive target, and a US quarter makes a good high
conductive target. TDI is a motion detector, so target responses
depend on the motion of the coil. If you hold the coil steady over
a target, the audio response will fade back to the threshold tone.
In some cases there is not enough mineralization to require
ground balancing (e.g. non-mineralized beaches), and Ground
Balance may be turned off. In this mode the audio response is
high for all targets.
Setting the threshold at an ideal level is essential for opti-
mum results with the TDI. Each person’s hearing and preference
may vary, but ideally you would set the threshold at a level that
allows for faint signals to peak out of the hum, without an ex-
cessive background chatter. The following is a representation of
the audio response, including a low conductor response, a high
conductor response, and random noise:
The ideal no-noise response is what you would get if you dis-
connect the search coil. Any-thing above the ideal response will
have a high tone and anything below the ideal response will have
a low tone. If there is a lot of EMI or the Gain is set aggressively
high this can result in a lot of audio chatter.

16
In certain situations such as beach hunting, or prospecting for
gold nuggets, one should “dig it all.” The reason for this is the
wide range of target sounds that different types of gold nuggets
and jewelry can produce. However, in many cases the biggest
hurdle a treasure hunter faces is human trash - bottle caps, iron,
bobby pins, and pretty much anything else you can think of.
Your ears are the best discriminator available, and after using
the TDI for some time they will begin to learn to listen for the
subtleties in audio responses. In particular, pay attention to the
tail end of signals. You will nd that good targets produce a nice
clean sweep of a signal, whereas junk tends to produce a broken
or warbly sound with more variation at the end of the tone. But
remember that every signal you left undug could be a good one.
This is why when rst starting out, digging every signal can
really help you learn your machine. Each target dug will have a
sound to remember, and after some time digging junk you will
learn what each target’s audio ngerprint is, alowing your ears to
discriminate more effectively.
Threshold also has an effect on how much noise gets through
to the audio. A moderate threshold lets some of the noise through
(anything in the gray region is suppressed):
In this case you will hear a moderate amount of chatter, de-
pend-ing on the Gain setting. Weak target signals may come
through but may be indistinguishable from noise.

17
A lower threshold makes the TDI quieter and less chattery
but also requires a stronger target signal to produce a tonal re-
sponse:
A lower threshold can be played off against a higher Gain set-
ting, although you may nd that the net outcome is about the
same.
Setting the threshold exceptionally low can result in a “silent
search” audio, whereby there is no audio sound until a target is
detected:
The drawback is that sensitivity can be markedly reduced and
weaker targets completely eliminated. However, Gain can be
increased to counter this, though the net result is still likely to be
less sensitivity than an optimally adjusted threshold.
Pulse Delay
Sampling as close as possible to the end of the transmitted
pulse gives the highest sensitivity to all metal targets regardless
of their size or conductivity. As the Pulse Delay is increased to-
ward 25μs low-conductive targets will drop out, leaving only the
more high-conductive targets.
Conductivity is not the only factor that determines how tar-
gets respond; size, thickness, and shape also have a strong inu-

18
ence. Sub-gram gold nuggets are often only detectable at the
lowest delay setting while larger nuggets, even of the same alloy,
can be detected at higher delay settings. This is largely due to
skin effect, whereby the response of small thin targets dissipates
quickly.
A good exercise is to experiment with different targets at
different Pulse Delay settings. This is best done with the Ground
Balance switched off so that all targets sound the same (no two-
tone response) and the sensitivity to the target can be more eas-
ily observed. After you determine how the Pulse Delay affects
the signal, you can try the same tests with the Ground Balance
turned on to see whether the target produces a high tone or a low
tone. You can then use your ears to eliminate or accept a target.
In some soils the minimum pulse delay cannot be used. Nota-
bly wet salt soil (such as a saltwater surf zone) behaves like a
low-conductor target and will respond regardless of the Ground
Balance setting. Increasing the Pulse Delay to about 15μs will
eliminate wet salt response. However, as you move out of the
surf zone onto dry sand remember you can reduce the Pulse
Delay to maximize sensitivity as dry salt sand does not cause a
problem. Areas with high concentrations of black sand may also
require an increase in the Pulse Delay.
Any changes to the Pulse Delay setting affects the ground
balance point so the TDI will need to be re-balanced.
Dual Field Coil
With any metal detector, the size of the search coil presents a
trade-off between depth and sensitivity. A larger coil offers better
depth on larger targets at the expense of small-target sensitivity,
and a smaller coil has better sensitivity to small targets, but at a
lesser depth.
Detectable gold nuggets can range from several grains to
multiple ounces, so a coil that offers both depth and sensitivity
would be ideal. TDI uses a patented dual eld (DF) coil which

19
literally gives you two different size coils running simultane-ous-
ly: a larger outer coil for large target depth, and a smaller inner
coil for small target sensitivity. As such, even the 12” DF coil,
with its 6” inner coil, can pick up nuggets of only a few grains.
Proper sweep technique is important with any detector, and
the DF coil adds a slight twist. Round coils tend to have a coni-
cal pattern of sensitivity as illustrated below. As such, coverage
at maximum depth is less than the size of the coil, so it is always
recommended that successive sweeps are overlapped by about
50%.
The DF coil has an additional inner coil which has its own
conical detection pattern. Since this coil is most sensitive to shal-
lower tiny targets that the larger coil may miss, in order to get
the best ground coverage on these targets it is recommended that
the 50% overlap be applied to the inner coil, as illustrated above.

20
Besides overlapping each sweep, it is important to keep the
coil close and parallel to the ground. Pendulum-swinging the coil
results in loss of depth, and if the ground balance isn’t perfectly
set the variation in loop height will create a ground response.
The following illustration shows improper and proper coil sweep
motion.
Wrong Right
Dealing with Noise
Because PI detectors have wideband receivers they are
more prone to noise and interference than narrowband VLF
designs. There are a few strategies for dealing with noise. First,
TDI has a Frequency Offset control that slightly adjusts the
overall pulse rate. With the Threshold and Gain turned up to the
point of mild chatter, make very small incremental adjustments
to the Frequency control to minimize the chatter.
Some sources of noise cannot be dealt with electronically,
such as electric fences. Try to identify the noise source and dis-
able it. Indoor testing is notoriously difcult to do with PI