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!