Fisher Gold & Treasure Detectors | Dave Johnson's Essays



Question and Answer Session with FT-Fisher Engineers David Johnson and John Gardiner

From left to right:
Mark Krieger, New Product Development Engineer
John Gardiner, Electronics Engineer
David Johnson (kneeling), Chief Engineer
Jorge Anton Saad, Electronics Engineer




First of all, I want to thank Tom Walsh, Mike Scott, Tricia Richardson, Dave Johnson and John Gardiner for their help in arranging this interview. I think it’s a fair statement that First Texas – Fisher is one of the most exciting metal detector companies on the planet right now, and as such, has piqued the interest of the hobby detecting world in a way that hasn’t been seen for quite a while.

I had the idea for this interview months ago, before I had started this web site. There was quite a buzz in the forums when rumors started of a new Dave Johnson design coming from First Texas under the Teknetics moniker. After the subsequent release and success of the T-2, the hobby community was set on fire with excitement over the prospects of “things to come”. Another wave of excitement hit when it was learned First Texas had acquired Fisher, and that wave turned into a tsunami with the release of the F-75. Mr. Johnson was quick to point out that the T-2 and F-75 were team efforts, not solo projects, and that Engineer John Gardiner was key to the success of both machines.

The purpose of this interview is to give the fans of metal detecting a “behind the scenes” glimpse of the engineers who designed the T-2, F-75 and F-4. There is an unusual “connection” people in this hobby have with their metal detectors. Over time, they seem to take on a personality of their own, becoming an extension of the owner/user. Because of this “personal” connection, most view the responsible engineers with a sense of awe and mystery. I feel that “getting to know” the Engineers will help people appreciate and applaud the outstanding efforts of these geniuses behind the scenes.

All questions below are for both Mr. Johnson and Mr. Gardiner, unless otherwise designated.


Question 1:

DS: What got you interested in engineering metal detectors?

Dave: "In the early 1970’s I was working for CALTRANS doing traffic census. Some of that work involved inductive loop vehicle detectors. I got tired of hauling a 150-pound box of lead-acid batteries around to power them, and prototyped a vehicle detector that ran off a single 9-volt “transistor battery”. It was too unstable to be useful, but to my surprise it discriminated between cars and trucks. Then I got transferred to another department and abandoned work on the vehicle detector.

In 1981 I was hired by Fisher Research Lab, which at that time was in Los Banos, California. I’ve been working in the metal detector industry ever since."

John: "After I graduated from UTEP I landed a job with First Texas Manufacturing. I started working on the different model for Bounty Hunter line. "


Question 2:

DS: How do you feel about the excitement amongst metal detecting hobbyists generated by the T-2 and the F-75?

Dave: "We intended for the T2 and F75 to be exciting products. We’re pleased that our effort was a success.

Not all metal detectors are supposed to be “exciting”. Many are revisions of established familiar products, and customers buy them because there’s a good track record behind them. Some products are new and different enough to generate a lot of interest, like our new F4. It’s getting a lot of attention because it’s a new combination of stuff that offers uncommonly good performance and features for the price. But it doesn’t generate the kind of excitement that major technological advances do."

John: "I was very pleasantly surprised at how fast the T2 popularity has grown."


Question 3:

DS: How difficult was it walking the line between superb ergonomics and weight vs. structural durability (on the T-2 and F-75)?

Dave: "It took a lot of attention to detail. I was originally shooting for even lower weight. I’ve been studying the physiology of metal detector ergonomics for my whole career and on this product I had a blank check to get it right. There were things we had to do to get the ergonomics right that added weight. We were all betting that good ergonomics was more important than shaving every ounce, and the T2 and F75 proved us right. Nobody is saying we should have made it lighter."

John: "I really did not get to involved with this issue."


Question 4:

DS: Do you guys metal detect as a hobby? If so, what’s your favorite “find” to date?

Also, what are your other hobbies?

Dave: "I don’t detect as a hobby, but enjoy field testing units with people who really know their stuff. I especially enjoy field testing gold machines because both my grandfathers were gold prospectors and I inherited from them some of that love for geology and the desert.

My main hobby if you can call it that, is being successful at treating the supposedly “untreatable” Lou Gehrig’s Disease (ALS), and helping other ALS patients do the same. If anyone reading this has ALS or knows someone who does, I invite them to contact me at and mention “ALS” in the subject line so I’ll know it isn’t spam."

John: "I don’t detect as a hobby, but do have a unit that I use at home.

My other hobbies are bike riding and reading."



Question 5:

DS: Would you mind giving us a list of detectors you’ve had a hand in developing?

Dave: "Old Fisher: 1260, 1220, 1210, 1225, 1235, 1265, 1266, 1280, Impulse, CZ6, CZ5, CZ20, Gold Bug, Gold Bug II, TW6/Gemini, FX-3, and several industrial products.

Tesoro: Diablo MicroMax, Lobo Supertraq.

White’s: DFX, Beachhunter ID, GMT, MXT

Troy: Shadow X5

Bounty Hunter & related products: nearly everything we manufacture. Many of these products are adapted from the original Teknetics which was designed by George Payne. The Teknetics T2 however was an entirely new design.

New Fisher: F75, F4, and everything else since then.

On most of the above I was the lead engineer. On the White’s DFX and Beachhunter ID I developed the multiple frequency circuitry, and other engineers designed products around that circuitry. In addition to the above there are many products on the market which are adaptations by other engineers of products I designed."

John: "Bounty Hunter : I have had a hand in most of our current line up from the bottom to the top, from Guardian to the Time Ranger.

Teknetics : T2 I was main programmer

The Fisher’s : The F4 and F75"

Question 6:

DS: Are we about “maxed out” as far as how deep VLF units will go? In your opinion, what’s the biggest obstacle for current technology in achieving increased useable detection depth?

Dave: "Getting extra depth out of a VLF, multifrequency, or PI machine is very difficult, because these machines follow an inverse 6th power law relationship between signal voltage and depth. If everything else is maintained equal, doubling the depth requires 64 times as much signal. If this is done by increasing transmitter power, doubling depth requires 4,096 times as much battery drain. That’s the basic reason why depth increases come so slowly in this industry.

The biggest impediment to getting usable depth in the ground, is interference from magnetic and electrically conductive minerals in the ground, which can produce signals hundreds of times as strong as that of the metal target you’re trying to detect and hopefully identify. There are several approaches to extracting the metal signal from the ground mineral signal, but they all have their limitations. That’s why you see several different technologies coexisting in the market."

John: "Dave points out biggest obstacle which is seeing target through the Ground and Air interference."


Question 7:

DS: If you had to pick one existing feature on the F-75 that you’re the proudest of, what would it be?

Dave: "If we can include the T2, it’s a tossup between the ergonomics and the target separation. Both aspects of the design were huge leaps forward.

If you mean just the F75: the fact that on the F75 we pushed sensitivity even further than on the T2. As I said a few questions back, more sensitivity is very difficult to get in this industry."

John: "One of things I like best about the F75 is it has the ability to give I.D. values while in static mode."


Question 8:

DS: Are TID pulse units the hobby future? Or, what do you think will be the next great advancement in metal detector technology?

Dave: "About 1985 I built a real sweetheart of a discriminating PI unit, not very hot in air test, but it was simple, lightweight, powered by one 9 volt “transistor battery”, ran quiet in bad ground, had no bad habits, and you didn’t have to dig any trash. It morphed into a fully static TID machine which Fisher came close to releasing about 1989, but its reliance on fully static operation which was supposed to be an advantage, was in fact a fatal flaw for a TID machine. Stripped back down, it became the Impulse which was strictly all-metals.

Industry insiders know about a PI TID machine which a fairly sharp freelancer has had under development for about 5 years and which is said to be nearing production. Whether or not that one makes it, I expect there will eventually be others.

The next great advancement in metal detector technology will be….. ahem… we’ll all know when whatever it is actually hits the market and customers say it’s a great advancement. I hope that when that event happens, it’s got our trademark on it. If it’s got someone else’s trademark, I guess we’ll just have to play leapfrog."

John: "At this point I will reserve comment."


Question 9:

DS: "Crystal ball" time… if you had to take an educated guess, what do you think hobby detecting hardware will be looking like 10 years from now? (Operational and physical)

Dave: "Everything will look like a T2/F75 clone.

Just kidding! Actually, I do expect machines to show up on the market looking a lot like the T2/F75. But, there will always be a lot of variety in what machines look like and how they’re designed to be used. Some machines 10 years from now will probably look about the same as they do today. The Tesoro Micromax is such a good basic mechanical design that it or something similar will still be around 10 years from now.

Operation? The basic 2 or 3 knob VLF motion discriminator has been around for almost 25 years and does very well what it’s supposed to do. It’ll probably still be around 10 years from now. Predicting what the leading edge high end machines will be like 10 years from now is a lot more difficult because the path as yet untrod offers so many surprises.

To put this in perspective, 25 years ago I was predicting the impending demise of single-frequency metal detectors. 16 years ago Fisher introduced the CZ and Minelab introduced the Sovereign, both of ‘em multiple frequency machines. But single-frequency metal detectors kept getting better, and in 2007 the happiest F75 owners are the ones who already have a multiple frequency Minelab Explorer."

John: "With advances in display technology and RF technologies. They should be lighter and even more ergonomic than the T2."


Question 10:

DS: The “halo effect”… fact or fiction?

Dave: "Mostly fiction. A lot of what people attribute to “halo” actually has to do with what happens to the natural magnetic and conductive structure of the soil matrix when you disturb it.

The rust that remains from a rusting iron object is definitely a “halo” which can have a definite effect on detectability and on target ID.

Corrosion from nonferrous metals is essentially neutral to metal detectors and is present in too small an amount to affect detection. It is plausible that the electrochemical corrosion process of nonferrous metals influences the geochemistry of the iron minerals in the immediate vicinity of the target; however I doubt that such an effect would be sufficiently prominent as to influence detectability.

Nonetheless, there are a lot of beeperists whose actual field experience leads them to believe that the halo effect is real, independently of the question of whether the conventional explanation (“conductive corrosion products”) is right or wrong. I’ve been around the block enough times to have encountered things which seemed impossible and yet there they were. One of these days I may have to eat my words about “halo effect”."


Question 11:

DS: “Detectable depth of a target cannot exceed the diameter of the coil” ie: 8” coil goes 8” deep. Agree or disagree?

Dave: "Not true. Most metal detectors will detect a manhole cover at least 2 feet deep, and most won’t detect a 1-grain gold nugget 1 inch deep. Small coils usually detect deeper than people expect them to, and large coils usually buy you sweep width rather than additional depth."

John: "Disagree. We already have a unit that with a 4” coil can detect coin size objective at 6”."


Question 12:

DS: What new, top-secret detectors are you currently working on? (HA! Just kiddin’)

Dave: "The Eta-Kappa. No kidding. So what’s an “Eta-Kappa”? Sorry, can’t tell you."

John: "Ha Ha!"


Question 13:

DS: What’s the working environment like at First Texas?

Dave: "Love it. Flat organizational structure, there’s no engineering dept. manager, we all work for Tom. Tom is a very smart fellow, eager to innovate, very much in charge and yet doesn’t micromanage, flexible enough to change course when it’s necessary, listens better than just about any other boss on the planet, and doesn’t sweat the small stuff as long as things are getting done that need to be done.

Oh yeah, also the air conditioning in engineering dept. works real good during hot weather.

You didn’t ask how I like El Paso. Love it. Decent climate, desert mountains to hike in, friendly people, low crime rate, low cost of living, and great Mexican food.

We also have the nation’s stupidest ex-mayor. Joe tried to get through airport security packing a loaded pistol…….. His excuse? “But I have a concealed weapon permit.” Yeah, right, here’s your piece back, proceed to your boarding gate? I don’t think so!"

John: "It’s a good environment, we are always looking forward while learning from our past."


Question 14:

DS: (For Dave Johnson) Can you tell us about how FRL came up with the innovative 1200 series design, which really set the bar for “balance” over the heavier “lunchboxes” of the 80’s?

"When I came to work for Fisher in February of ’81, Fisher was just about dead. They knew they needed new product. They didn’t have anyone in house who could design the guts, so they got to work on the mechanicals and hoped to hire someone who could design the guts. That someone turned out to be me. We introduced the 1260 in late spring of ’82, and it was a revolutionary machine for its time. Credit for the mechanicals goes to Dick Williams, Marvin Jones, Jim Lewellen, and Carol Chandler. They got a heckuvalotta stuff right."


Question 15:

DS: Do you have a collection of different coins and trash items in your engineering department that you test target ID with? How about test beds/gardens with different soil types? Do you rely heavily on field testers for soil type handling information?

"The old Fisher site in California had a carefully designed and constructed test bed with several different sections where we imported different soil minerals so we could emulate almost any mineral condition besides alkali or salt water. It was an expensive undertaking which we haven’t replicated here in El Paso because we don’t own the premises.

In design, I rely heavily on my knowledge of soil mineral conditions around the country and how they affect metal detectors. We do limited field testing locally, but El Paso doesn’t have a wide variety of soil conditions. For design verification we rely on field testing by people in other regions who have in-depth experience with a number of metal detectors and who are articulate in explaining what happens during field testing."


Question 16:

DS: Do you follow the online detecting forums and do you feel these help to promote your product and the hobby?

"There are several detecting forums that I take a look at almost every day. They’re good for the hobby, and they’re also a valuable source of information for us. I don’t post on the forums, because I don’t have time to get into nonsense arguments with people. Once in a while when we feel it would be beneficial for information to be posted on a forum, for instance to get a stupid rumor straightened out, we leak the information semi-officially to people who are already active on the forums and give them permission to post it if they feel like it."


Question 17:

DS: (For John Gardiner) Mr. Gardiner, in the 70’s and early 80’s there was a detector company, “Gardiner Metal Detectors”, with huge rods and search coils… any relation?

John: "Not that I know of"


Question 18:

DS: There’s been a lot of emphasis on the DD coil design for the new Teknetics and Fisher machines. What was your main motivation for going DD versus concentric?

Dave: "Better ground penetration. And some other stuff. ‘Nuff said about that."


Question 19:

DS: Iron separation seems vital nowadays & perhaps more important than depth. Can detectors truly “see thru the iron”, or is “unmasking” best achieved at this point with smaller or DD coils?

Dave: "Mostly yes on all counts."

John "Nice one Dave."


Question 20:

DS: Seems specialized detectorists feel frequency/khz is so important now, claiming a 7khz Coin$trike for example is for coins not relics. Is 13khz great for all-around hunting, & why don’t we see say 25khz units for relic hunters?

"In general, higher frequencies are better for smaller and lower conductivity stuff, and lower frequencies are better for larger and higher conductivity stuff. Relic hunters are generally looking for stuff that is smaller or lower conductivity than US clad, copper, and silver coinage. However, frequency is not critical, and a 7 kHz machine can be good on relics and a 13 kHz machine can be good on coins.

Metal detector manufacturers generally avoid the 20-30kHz range because of electrical interference from military communications."


Question 21:

DS: There have already been two new models released for Fisher in the past 5 months, the F-75 and the F-4. Is this a sign of things to come?

Dave/John: "Yep."


Question 22:

DS: Are there any tricks or tips for the F4, T-2 or F-75 you’d like for users to know about?

Dave: "The F4 is pretty straightforward. Only tip is to use autotune all metals if you’re in an area that’s relatively free of trash to locate targets, and then switch to discrimination to ID them. You’ll get more deeper stuff that way.

The T2 and F75 are very sensitive machines, which makes them more vulnerable to electrical interference than a less aggressive machine like the F4. And, the T2 and F75 incorporate a number of improvements in discriminator design, some of which affect sensitivity independently of the sensitivity control setting. This caused more confusion than we expected. Fortunately most owners are getting used to it.

My personal recommendation is to select the discrimination process you want, then dial in the discrimination level you want, then set any notches you want, and then after doing all that set the sensitivity setting just below the edge of noise. Don’t be afraid to crank the sensitivity ‘way down if necessary: the T2 and F75 are still hot machines even at low sensitivity settings."

John: "Slow down and listen to what the machine is telling you."


Question 23:

DS: There are lots of forum rumors floating around in regards to the possible return of a Fisher water detector…. Any comment?

Dave: "Marketing dept. has released information indicating that a water machine called a “CZ-21” is in the works."


Question 24:

DS: What’s the most challenging part of designing metal detectors for the hobby market?

Dave: "Psychology."



DS: Do you have any parting words for all the readers and metal detecting fans at large that are following your work?

"We’re building on a legacy that was created by many people. The progress we make is the work of many people. Of these many people, most never get any credit other than a paycheck and maybe a thank-you.

I would like to name two of those unsung heroes. Javier, who assembles prototype boards faster than anyone else on the planet and somehow does that while making no assembly errors. Aurora, who worked hard to make sure every T2 went out right, even while she was losing her fight with cancer.

First Texas Products is still benefiting from the genius of George Payne, whose basic target ID system has gone into more metal detectors sold, than all other target ID systems put together. Thanks, George.

Finally, I would like to thank my former employers for the privilege of having worked for them."

DS: Thanks again for taking the time to answer these questions! I have no doubt folks will thoroughly enjoy reading your responses. In closing, if there’s a question, that as you read this you thought “Now why didn’t they ask *blank*?” please feel free to add it and I’ll make sure it’s included on the site!

“What are your favorite designs?”

Dave: "This will probably surprise you. My all-time favorite designs are the Tesoro Diablo Micromax, and the little Bounty Hunter two-knobber that goes by several different names and retails in the $55-75 range."

John: "My favorite unit so far is the Land Ranger. The T2 come in at a close second."


We hope our readers have enjoyed this interview as much as we have! I want to personally thank the great folks at First Texas /Fisher for allowing us to interview Dave and John. These two gentlemen are extremely busy, and taking the time out of their hectic schedules for this is hugely appreciated! Special thanks also goes out to Bill Ladd who thought up quite a few of the great questions for the interview.

Thanks again,

Mark Ellington & Bill Ladd


from left to right:
Mark Krieger, New Product Development Engineer
John Gardiner, Electronics Engineer
David Johnson (kneeling), Chief Engineer
Jorge Anton Saad, Electronics Engineer