Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector
By Andy Sabisch
From Page 24
June, 2009 issue of Lost Treasure

Fisher Research Laboratory, the industry’s oldest metal detector manufacturer, has been building metal detectors since 1931 for commercial and recreational users. Their engineers have developed many ground-breaking advances found on virtually all other detectors today including silent-search searching, slow-motion VLF-discrimination, the S-shape handle, and “turn-on-and-go” operation. The CZ Quicksilver circuitry, first introduced more than a decade ago, quickly gained the reputation of being able to handle even the most challenging of ground conditions while providing above-average detection depth. Expanding from the land-based models originally introduced, Fisher developed a fully waterproof model called the CZ-20 which became a mainstay for water hunters worldwide.

Recently the hobby’s business landscape changed, and in 2006, the original Fisher company was acquired by First Texas. Despite this acquisition, the First Texas has maintained the Fisher commitment to producing first-rate equipment for the most demanding detectorists and taking the company into new directions using the latest technology available.

The CZ-20 was one the models that was revisited and had several changes made to address certain issues that had been identified over the years. Since I’ve been a Fisher CZ fan since they first came out (and actually wrote a book on the entire line for Fisher in the mid-90’s), I was looking forward to giving the new CZ-21 a workout.


The CZ-21 is a dual-frequency VLF detector designed to be equally at home on land as it is 250 feet below the surface. Designing a detector to operate reliably in the water is a challenge for any manufacturer due to the rigors water-hunting places on the equipment. Any leakage can kill the detector in short order and salt water is even more damaging to the circuitry inside the case. Over the last few decades, there have been water machines that faded from the market due to leakage issues; however, since the introduction of the 1280-X in 1985 and the CZ-20 several years later, Fisher has been recognized as having a design that is virtually bullet-proof when it comes to remaining watertight with minimal maintenance. A feature unique to the Fisher lines is the separate battery compartment. The CZ-21’s battery compartment is entirely separate from the electronics, so in the event any water gets past the O-ring protecting the batteries, the most you will need to do is replace the batteries . . . no water can reach the electronics!

The CZ-21 is a VLF-detector that shares its "Fourier Domain Signal Analysis System" circuitry with other Quicksilvers - past & present. This circuit transmits signals at two different frequencies simultaneously (5kHz and 15kHz), resulting in a high level of performance that provides accurate target identification and improved detection depth in even the most highly mineralized or salt-laden ground.

The mention of target ID capabilities in a report on a waterproof detector may catch the attention of many readers. The CZ-21 features the familiar 3-tone CZ audio target ID system which allows the user to identify targets with a high degree of accuracy and decide if they are worth recovering. Iron will produce a low tone, pull tabs, tin foil and most gold rings will produce a medium tone, and silver objects, large gold jewelry and U.S. coins (including nickels) a high tone. The on-line version of this report will cover techniques that can be used to increase the number of gold rings and other pieces of jewelry you can find per hour in the field though the use of the CZ-21’s audio target ID system.

Operation of the CZ-21 couldn’t be simpler. It is controlled through four knobs and a push-button located on the face of the control housing. The VOLUME control also turns the unit on, and, if turned past “5”, activates the Faint Target Audio Boost which amplifies weaker signals from smaller or deeper targets while holding the response to larger targets constant. Many beach hunters have found deep, valuable targets using this feature.

The DISC control has seven distinct settings which allow the user to select both the level of discrimination to be used as well as the operating mode to search in. Selecting a setting of "0" thru "6" activates the silent search motion discriminate mode with the amount of discrimination determined by the value selected. Placing the knob in the position labeled AUTOTUNE will activate a VLF motion all-metal mode. While this mode does not provide any discrimination, it does give a wide-scan search field with a slight increase in detection depth over the motion-discriminate mode. In areas which do not contain a great deal of trash, this mode would be the preferred search mode.

The SENSITIVITY control also serves two functions. Turning it fully counterclockwise, battery strength can be checked by listening to the resulting audio signal. When searching with the CZ-21, the higher the SENSITIVITY setting the more sensitive the detector becomes. Remember however, that if it starts to operate erratically, drop the control until the chatter is eliminated. Additionally, when in the AUTOTUNE position, the SENSITIVITY control also adjusts the audio threshold.

The final knob labeled GROUND is used to precisely compensate for the mineralization present in the search area in conjunction with the PINPOINT pushbutton. Ground balancing, even in areas containing black sand or salt water, is a quick and simple process even underwater and is well explained in the manual.

As with many of the Fisher detectors, there are preset marks on all of the controls making it easy to start hunting immediately after unpacking the detector.

The CZ-21 has been designed as an all-purpose detector for uses ranging from land hunting (especially in adverse weather conditions) to beach & shallow water hunting to scuba diving. Unlike other detectors that require portions of the shaft to be added / removed depending on they type of hunting one plans to do, the CZ-21 can be easily adjusted from 30” to 50” thru the use of the unique 2-piece fiberglass shaft.

It can be purchased with your choice of either an 8” or 10” search coil. There are advantages and disadvantages to each size; however, in general, the smaller the coil the more sensitive it will be to small targets and the more effective it will be in separating good targets from trash buried nearby. The larger coil is more suited for wreck divers or hunters that desire a slight edge in detection depth over their competition. Consideration should be given as to which coil size is desired as they are not interchangeable and the larger coil does produce more drag when swinging it in shallow water.

If weight is a concern (as waterproof detectors tend to be heavier than land-only detectors), the control housing slides easily off the shaft and can be hip mounted in a matter of seconds with the belt clip that comes with the unit. When hipmounted, the handle & search coil weighs around 2.5 pounds which allows the CZ-21 to be used for hours without fatigue.

The CZ-21 is powered by four 9V batteries and a quality set of alkalines can operate the detector for upwards of 50 hours. Rechargeable batteries can be used; however, the battery life will be noticeably reduced. NOTE: When re-installing the battery compartment cover, ensure the O-ring is oriented correctly and that the seating surfaces are clean and undamaged to prevent leakage.


As with any new detector, the first thing I did was conduct some air testing to see where specific targets registered and the audio response each produced. My results confirmed what was shown in the manual and what my past experience with CZ’s had been. The next stop was the test garden. I’ve found that in most cases, the easiest way to ground balance a CZ is raise the coil off the ground, set the GROUND BALANCE control to “10”, tap the PINPOINT button and lower the coil to the ground. Slowly turn the GROUND BALANCE control clockwise until you start to hear a slight tone. Simply back off until the tone just disappears and the detector is perfectly balanced. All of the targets in my test area produced clear, repeatable signals and were accurately identified via the audio ID system. Unlike some detectors where optimal performance is closely tied to sweep speed, even the deepest targets were detected at sweep speeds that ranged from very slow to quite fast making the CZ-21 well suited for applications ranging from slowly scanning a sunken wreck to whipping the detector across the beach in a seeded hunt.

My family has come to realize that when it comes to metal detecting I’m a bit fanatical so when I announced I was going up in a steady rain to test the CZ-21, I got little more than a questioning glance and the comment “Dinner would be ready in a few hours.” With a steady rain for the past few days, I figured the conditions would be a good test of how the detector performed at a land site.

I had permission to hunt a wooded area that had a few old foundations scattered about and this was where I headed. Opting for the target-ID search mode, I set the DISCRIMINATE control to “0”, SENSITIVITY to “9” and quickly ground balanced the CZ-21. Signals were plentiful; however, most were iron and were easily identifiable by their audio response. A mid-tone signal surrounded by low-tone iron signals near a large tree sounded promising. Clicking the DISCRIMINATE knob to “1”, the iron signals were rejected yet the mid-tone signal still came through. This was a good sign that when using iron-elimination, very few good signals would be missed due to masking. The signal turned out to be a flat button from the early 1800’s. The pinpoint mode worked extremely well and the VCO audio allowed me to zero in on signals with a high degree of precision. Two hours in the pouring rain produced several “keepers” including 2 more buttons, a copper disc which may have been a coin, a few round balls and a silver plated spoon from depths up to 10 inches.

The next site I visited was actually a water site . . . an informal swimming area on a lake about 35 miles away. Unlike many of these type of beaches, this one was not littered with trash which made hunting enjoyable rather than a chore. The sand / mud allowed targets to sink quickly so I was hoping the CZ-21 could pull more targets from areas my partner and I had already searched. Wanting maximum detection depth, I opted to search in AutoTune. Setting the SENSITIVITY at “10” and ground balancing, I waded in to water. Based on the chatter, it was clear that “10” was too high and dropping it to “8” produce stable operation. Signals were fairly plentiful and coins at had clearly been there for years turned up on a consistent basis. A useful trick when hunting in AutoTune is to click the DISCRIMINATE knob into the “0” position when a target is detected to take advantage of the audio target ID system. Many of the targets I recovered were in the 8” to 10” range and produced solid, repeatable signals.

The day before this report was due I was able to return to the beach and strap on my SCUBA gear to see what was out past where the bottom dropped off. Collapsing the shaft made it the ideal length for diving without the need to remove portions of the shaft as many other dive detectors require. Dropping to the bottom, I checked my depth gauge and saw 25’. Volume was more than adequate to be heard over the bubbles from the regulator and I picked up a nice pile of targets during my dive including a 14KT gold mans ring with 13 diamonds (OK, real small diamonds).

The on-line version of this report contains additional field test data as well as more technical information on the detector itself.


There’s an old adage that says “If it ain’t broke, don’t fix it” and in the case of the CZ-21, the engineers at First Texas kept that in mind as they brought out this latest addition to the Quicksilver line. The redesigned face plate with the new pinpoint button, a new gasket system, and improved circuit board protection built on a proven design that works better than its predecessor. To repeat what I said about the CZ-20 in my original field test, the CZ-21 is truly a detector that performs just as well submerged in salt-water as it will in a fresh water lake, a schoolyard, park, battlefield or mineralized ghost town. If you are looking for a single detector that will provide above-average performance in a wide variety of applications regardless of the weather conditions, the Fisher CZ-21 definitely fits the bill.

When the CZ-21 was first introduced, there was a manufacturing “glitch” that resulted in a number of units being released that would not ground balance properly and these units were recalled and repaired. Thanks to the Internet, word quickly spread about the “problem” with the new CZ-21 and some would-be buyers shied away. In talking to First Texas, this issue was corrected many months ago and all of the CZ-21’s being shipped are functionally tested and checked by a QC group before they leave the factory. The build quality of my CZ-21 was 1st rate and with a bit of care, will easily be in use a decade from now.

The CZ-21 metal detector comes with a limited 2-year warranty, which is on-par or better than other underwater detectors on the market showing that the factory is confident that it will hold up under virtually any condition one might use it in. A padded, lockable hard-sided carrying case is available as an option for added protection.

For more information on the new CZ-21 metal detector or any of the other models in the Fisher line as well as the name of your nearest authorized dealer, contact the factory at 1465-H Henry Brennan Drive; El Paso, TX 79936, call them at (915) 225-0333, or visit their website at Be sure to mention you read about the CZ-21 in Lost Treasure Magazine.

Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector
Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector
Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector
Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector
Fisher Research Laboratorys Cz-21 Quicksilver Metal Detector

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