Field
Test by Ben Myers
(Reprinted
with permission from Western & Eastern Treasures,
Pages 45-50, March 2000)
Tired of those pesky false signals that your VLF
machine makes over wet salt and black sand? Pulse induction (PI) could
be the answer, and Tesoro's exciting new PI model is called the Sand
Shark.
The folks at Tesoro have chalked up many impressive achievements in
recent years. Their development of ultralight, high performance land
detectors has drawn praise from many detectorists. Now, with the release
of this machine, they can also boast that, "The Sand Shark is
the first Pulse Induction metal detector that is controlled by microprocessor
technology." Let's take a closer look at what that means for
you.
In the past, one chore the PI searcher had to perform fairly frequently
was tuning the detector to keep it at peak performance or risk missing
targets. With Tesoro's use of microprocessor technology, the detector
now keeps itself in tune, allowing one to concentrate on listening
for targets. Those experienced in the use of PI detectors know that
this is a real time saver, and maybe a gold ring saver as well. Peak
performance can be the difference between success and failure for
any metal detector, and Tesoro is forging ahead with modern technology
to make pulse induction operating a user-friendly experience. Now,
with microprocessors working for you, you just set the Sand Shark
to your preferences, then hunt on the beach or under water, leaving
the detector to handle circuit maintenance.
PHYSICAL DESCRIPTION
First of all, those of you who are divers won't have
to make any do-it-yourself pole and armrest modifications. There are
three sections of poles, which easily fasten and unfasten with spring
buttons and pole locks. This system provides for no wobble coil sweeping,
yet easy disassembly. For diving, remove the middle pole section and
slide the lower pole directly into the upper-the section with the
S-handle and padded handgrip. Another nice convenience for either
diving or beach hunting is the ability to place the control box on
the pole, under the elbow at the armrest, or mount it to body or belt.
The 8' of cable provided is sufficient for any configuration, and
control box removal is just a matter of depressing four of the spring
buttons and lifting off the control box. It is obvious that a great
deal of thought went into the ergonomic design.
SEARCHCOILS
The Sand Shark has a standard 8" open-center
searchcoil for most applications, plus a 10½" open-center
coil for larger targets and light trash, a 7" for smaller targets
ad trashier sites, and a 10" elliptical for a widescan sweep
while retaining good sensitivity to smaller targets. Being stuck with
a 10" coil in a trashy area where a small one would do nicely
is no picnic, and having the extra depth of a larger coil in a non-trashy
site is a blessing as well. Tesoro's exceptional Printed Spiral searchcoils
provide the best tools for the job at hand. Also, you will notice
that the target signal is strongest at the center of the coil for
easier pinpointing.
CONTROL BOX
The control box has a bracket mounted on the top.
Holes on either side of the bracket allow the spring buttons to be
pressed in and the control box lifted off the pole. If you prefer
it under the pole and in front of the handgrip for easier access to
the controls, it can be mounted there. Then again, if you'd rather
have the counterbalance of the control box under the elbow, it's a
"snap." The control box, as well as the entire detector,
is ruggedly constructed to allow diving to a maximum of 200'.
The Sand Shark comes with a set of attached, waterproof stereo piezo
headphones. Two draw-bolt clamps retain the face of the control box
for a watertight seal of the electronics. Eight AA batteries held
in a drop-in battery pack power the detector. The batteries are accessed
through the release of the faceplate clamps.
CONTROLS & FEATURES
Since PI units don't have to contend with ground
balance, they are usually simple to use. The Sand Shark has four control
knobs on the face that may look a little daunting at first, in fact
they are easy to set and actually make pulse detecting more comfortable
than ever.
The MODE control is the one we'll consider first. Mode is a word with
a number of meanings in the detector world, and in this case, it is
a way of adjusting the type of audio response of the unit. In the
extreme left position, the unit is OFF. The next setting is VCO (Voltage
Controlled Oscillator). The oscillator on the Sand Shark changes audio
frequency and amplitude as the target nears the coil. So, the signal
you hear through the headphones becomes louder in volume and higher
in pitch. This is my favorite way to hunt with the Sand Shark, as
there is no doubt that a target is nearby.
Skipping to the last notch, you'll find the NORMAL setting. In this
mode the audio signal keeps the same frequency you set, and the volume
of the audio signal indicates signal strength. Tesoro nicely considered
each person's hearing and provided an ability to preset the frequency
to be used in this mode. That is where the third slot of the MODE
knob comes into play, marked "F SET" for Frequency Set.
Place the MODE knob to "F SET," then look at the THRESHOLD
knob directly across from it, as it becomes a frequency adjuster to
set the tone of the NORMAL mode. You will notice that "F SET"
on the MODE knob and "F ADJUST" under the THRESHOLD knob
are both highlighted in orange to work in conjunction. After adjusting
the THRESHOLD knob with the corresponding "F SET" MODE knob
you will hear the audio tone you desire.
We will get to threshold setting in a moment, but for now, just remember
that once frequency is set and you have come out of "F SET,"
the threshold must be reset. Also, while the MODE knob is a "F
SET," the detector will not respond to targets (it must be in
either VCO or NORMAL.)
While discussing the THRESHOLD knob, perhaps we should explain to
new detectorists that "threshold" is the steady hum you
hear in the background. Some targets are so small or deep that they
may not be able to generate much of a change in the audio. Therefore,
a low, steady hum is the best setting of the threshold, as too loud
a threshold will not allow one to hear minor changes. Once the VOLUME
control is set, you can do a battery test. The volume should be adjusted
in accordance with conditions of the area to be hunted, and set at
a point that is comfortable for you.
The THRESHOLD knob has a slot marked "BATT. TEST" that checks
the condition of the batteries. The eight AA batteries will provide
10-20 hours of use with the PULSE WIDTH knob set at the "preset"
position. Six or seven beeps means that the batteries are A-OK, with
fewer beeps meaning that they are draining. Tesoro suggests replacing
the batteries at one or no beeps, but personally, I wouldn't wait
that long. Output power is especially important in a PI machine, and
you want all the performance available. Don't forget to reset the
threshold when the battery test is finished.
The PULSE WIDTH knob may be an unfamiliar one for some people. However,
the Tesoro engineers have wisely included it to give you more control
over battery life in relation to sensitivity. Some may disagree, but
I feel comfortable in saying that you can think of the PULSE WIDTH
as a kind of sensitivity control: the higher one turns it, presumably
the more sensitivity and depth. The downside is that the higher one
turns it, the more power is used and the less the battery life. The
nice part is that you control it. Depending upon the search, you decide
whether you need more battery life or more sensitivity to targets.
That explains the controls, and they are straightforward in design
and function. You decide and set for VCO with changes in pitch and
loudness, or NORMAL mode with the same audio frequency. Be sure to
check your battery condition and set the THRESHOLD and VOLUME levels,
as well as the PULSE WIDTH. After that , the detector takes care of
the rest. The user doesn't have to keep retuning the machine, because
microprocessor circuitry performs that job automatically.
UNDERSTANDING PULSE INDUCTION
With so many new people getting into the hobby, I
would be remiss if I did not say a few things about pulse induction
in general. After all, a better understanding of it will help you
get the most from the Sand Shark. PI machines are mostly an all-metal
detector. True, there are some that provide discrimination (trash
rejection) of higher conductive targets, but iron is often detected.
PI's are ordinarily used on beaches and underwater, where trash is
normally lighter and high discrimination should be avoided anyway.
Gold jewelry can show up anywhere from "iron" on up to "silver
dollar" on a conductivity scale, depending upon a number of factors.
This is true for all detectors. So, you want to dig all targets on
a beach, if you don't want to miss any jewelry.
VLF machines have to cancel out the effects of ground minerals while
sending out a constant electromagnetic field. When a metal target
disturbs the field, the imbalance is reported to the operator via
the circuitry. Most VLF machines have a real problem with wet salt
sand, and especially black magnetic sand-conditions where PI machines
excel. Manufacturers often say that PI units ignore salt and other
mineralization. I don't know that it is so much that they ignore them
totally, as that they ignore them long enough so that they don't pose
a problem. Unlike a VLF machine, a PI detector has a single antenna
that both transmits and receives. The batteries provide power for
the pulse coil to "turn on" and transmit an electromagnetic
field into the matrix around the coil. The matrix in the ground causes
eddy currents on both mineralization and metal targets encountered.
The transmitter antenna then deactivates itself and waits. After a
specified time the circuits activate, and the antenna becomes the
receiver for any residual eddy currents. The better an item conducts
electricity, the longer it will hold the eddy currents, and therefore
the more easily it can be picked up by the receiver antenna. Fortunately,
mineralization does not conduct electricity well, and therefore the
eddy currents decay quickly in the ground-whereas gold and silver
are good conductors and hold those eddy currents for the receiver
antenna.
OPERATION
To follow up on the previous paragraph, the receiver
antenna "activates" after the eddy currents in the mineralization
decay, yet is still detectable in metal targets. Longer transmitting
time allows more eddy currents on metal targets, and it is easier
for the receiving antenna to pick up these residual eddy currents.
This translates into more sensitivity and, as a result, greater depth.
Increasing the PULSE WIDTH creates a longer transmitting time of the
antenna, but also causes more power use and therefore less battery
life. The "Preset" mark on the Sand Shark's PULSE WIDTH
control gives the best balance between sensitivity and battery life.
All of this happens fast. In fact, the operating frequency of the
Sand Shark is 600 pulses per second! Why so many? Well, for one thing,
it allows the operator to use the Sand Shark more like a VLF machine,
in that one can use a faster coil sweep. There are reportedly other
reasons, but I can't comment on those within the scope of this report.
The Sand Shark utilizes Auto-Tune in the microprocessor circuitry
to keep itself tuned. For that reason, a very slight motion of the
coil is required at all times to receive a signal. However, it is
an extremely slight motion, and pinpointing is enhanced with the Spiral
Printed coils, which make that aspect of operation so easy.
FIELD EXPERIENCES
Although PI detectors can be used in fresh or salt
water, they are really in their environment in a saltwater location.
Many times a detectorist will be surprised to see a PI detector get
better depth on a wet salt beach than in an air test. I suppose everyone
has his own opinion, but mine is that this is due to the fact that
salt water is a good conductor of electricity. After all, the machine
is pulsing out electromagnetic signals, and the farther they can be
sent and received, the better.
About the time the Sand Shark arrived for testing, the east coast
was being pounded with some nasty hurricanes. Ordinarily, that would
be great, but it's several hours' drive to get to the beach from my
home; and at every opportunity to get time off from work, another
storm would hit and the beaches would be closed. Nevertheless, I did
get in two short trips to the seashore, and one to a freshwater lake
closer to home.
On the first trip to the seashore beach, I took a couple of minutes
to set up the Sand Shark and check the batteries. During the sweep
up and down the beaches, I tried both the NORMAL mode and the VCO.
I definitely preferred the VCO with the change in pitch; so, after
a while, I just left it on VCO. My field test took place after the
tourist season, so I should not have been surprised at the lack of
signals on the dry sand, where armies of detectorists had scoured
a depleting supply of coins and jewelry daily. Down at the water's
edge, though, there were still a good number of targets. I suppose
that the constant tide action kept making deposits in the "bank."
My very first target came up in the scoop, flashing the color of gold!
I was shocked. Unfortunately, closer inspection revealed that I'd
found a gold-colored earring, not real gold. Even so, the experience
did get me in the mood to find gold.
The next couple of hours turned up a fair number of coins and a fishing
sinker here and there. Most of the coins were from surface to about
8", and with the VCO the audio alerted me right away to the presence
of metal. I found two or three small pieces of iron, but it was a
clean beach except for the ever-present pulltabs. We all know that
pulltabs can "look" exactly like a gold ring to a detector,
so we tolerate the little rascals. I also noticed that there are fewer
pulltabs at the beach these days, and more of those little circular
foil liners from drink bottles. I guess they are going to be the pulltabs
of the next century.
Finally, as I was about to call it a day, real gold came up in the
scoop! The water was about ankle deep, and the ring was a wedding
band-small, but 14K and thus a keeper, with no owner markings. It
was about 5" deep and gave a good signal.
The next trip to the seashore was about the same as the first, between
storms but not the kind to churn up old coins. This time there were
more coins, and some of them had been there a while as they showed
the signs of salt-water corrosion. I was not to find gold on this
trip, but someone's house key "unlocked" the secret hiding
place of a silver religious medal close by. I am grateful for the
"gazillion" religious medals lost over the years, especially
silver ones.
Of course, the main reason for the trip was to use the detector, and
the Sand Shark was definitely doing its job of finding treasure for
me. The detector only weighs 4½ lbs., so fatigue was not a
problem. I had the control box on the pole, and if I had thought of
it, it would have felt even lighter if I had put it under the elbow.
Due to work situations, I couldn't get the time for more trips to
the seashore, so opted for a trip to a swimming lake in my area. This
was well after the swimming season, and I didn't expect to find much,
but the weather was cool and the sun was shining, and what more can
you ask? As predicted, there wasn't much to find except a few coins
and pulltabs. I was placing a tab in my trash pouch when an older
couple, taking a walk, came up to see what I was doing. "Find
anything?" they asked. How many times have we all heard that?
"Nah, just some coins and pulltabs."
They smiled and idly watched as I continued finding tabs. Then it
happened. The signal was not a "banger," but definitely
something interesting. It took two scoops at the water's edge to recover
it. About 10" down was a nice-sized 14K gold wedding band! There
are no initials inside the band, so guess who gets to keep it! After
I left the lake, I believe there was an open-mouthed older couple
on their way to a detector shop to make a purchase.
SUMMARY
Regardless of the detector you use, get out there
and enjoy it! But if you are in the market for a new water-hunting
machine, by all means check out the Tesoro Sand Shark. Believe me,
it's one shark that will put the bite on treasure!
Sand Shark Datasheet
View Instruction Manual
