Myers Depot Metal Detectors

Are all detectors generally the same

S

savage_sultin

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Hey all,
Thanks for the advice so far. I was wondering if all detectors pick up the same metals or are some specific to certain types?
 
They all perform the same basic task and I don't know of any metals they won't detect. (Unless you buy a piece of junk detector from China. (Don't buy a detector from Aldi's Food Store.))

There are machines designed for gold prospecting. Some are designed for beach hunting. But most detectors are designed for general purpose metal detecting; relics, coins, jewerly. These machines will also allow you to ignore certain items (like nails and pull-tabs). They will all beep when a good target is found. Some have visual displays. No detector correctly identifies what's in the ground every time.

The more bells and whistles a detector has determines its' price. Lower-priced machines are simple to use, some of these can see as deep into the ground as their more expensive brothers. They will come with a few basic 'programs'. These are modes of operation like 'coin mode', 'relic mode', 'beach mode', and 'all metal mode'. You can make minor adjustments to these modes. More expensive detectors give you more flexability, so you can do everything from finding big hunks of deep iron to finding tiny specs of gold.

If you go back and read past threads in the 'detectors and gear' forums, you'll learn a lot. Keep asking questions, but many of those questions have been answered in those old posts. You can also call any of the sponsors (their ads appear at the top of the page).

The hardest part of metal detecting is knowing where to swing the machine.

HH

Rich
 
The way I understand it the operating frequency of a detector plays the biggest role in its ability to detect different metals. The higher the frequency the more sensitive it is to small gold items but less able to handle mineralization. Or less penetration in the ground. The lower the frequency the better it can penetrate the ground and more sensitive to metals such as silver and copper. The down side being its less sensitive to small gold metals.

Most all purpose detectors use a frequency around 6khz. Detectors best suited for prospecting generally operate from 12khz-50khz. Some high-end detectors such as the DFX and Explorer series attempt to give you the best of both worlds by operating with 2 or more frequencies simultaneously.

In general I think the basic function of detectors is pretty much the same. The FCC regulates the output(RF) so the big difference would be the frequency they use and features.
 
Detector said:
Most all purpose detectors use a frequency around 6khz. Detectors best suited for prospecting generally operate from 12khz-50khz. Some high-end detectors such as the DFX and Explorer series attempt to give you the best of both worlds by operating with 2 or more frequencies simultaneously.

In general I think the basic function of detectors is pretty much the same. The FCC regulates the output(RF) so the big difference would be the frequency they use and features.
Click to expand...

Hi,

Had to chime in. I don't agree, I do not think that the FCC is involved in metal detectors. 6 kHz, 12 kHz, up to 20 kHZ is within the range of human hearing. They radiate electromagnetic energy within a specific range, but not nearly extending into what is considered "RF". 50 kHz would be considered "ultrasonic".

After all, if you calculate the length of a 50 kHz half-wave dipole antenna, it comes out to some 9300 feet long. I don't think there is that much wire in a search coil. (Luckily!)

Dave
 
laserfocusguy,

I hate to disagree with your disagreement :p , but...

laserfocusguy said:
6 kHz, 12 kHz, up to 20 kHZ is within the range of human hearing. They radiate electromagnetic energy within a specific range, but not nearly extending into what is considered "RF". 50 kHz would be considered "ultrasonic".
Click to expand...

Those frequencies are within the VLF range (3 kHz to 30 kHz). The FCC has assigned frequencies as low as 9 kHz within the VLF range. Part 15 of Title 47 of the Code of Federal Regulations regulates unlicensed devices that may cause interference. This would include metal detectors, so the FCC does have a say in it.

laserfocusguy said:
After all, if you calculate the length of a 50 kHz half-wave dipole antenna, it comes out to some 9300 feet long. I don't think there is that much wire in a search coil. (Luckily!)
Click to expand...

It doesn't matter how much wire is in the search coil. RF is still emitted from the device.
 
Hobbes,

A couple of comments...

hobbes_lives said:
Those frequencies are within the VLF range (3 kHz to 30 kHz). The FCC has assigned frequencies as low as 9 kHz within the VLF range. Part 15 of Title 47 of the Code of Federal Regulations regulates unlicensed devices that may cause interference. This would include metal detectors, so the FCC does have a say in it.
Click to expand...

Yeah, I sure do know about Part 15. Have had to deal with it before from the other side of the coin (...must accept all interference it receives, including that which causes undesirable operation...) with my ham radio stuff. Had some problems with nuking my TV, computer speakers, etc. Luckily, my own stuff, not the neighbors :p

I think metal detectors fall under Part 15 from the standpoint of that if they receive stray RF from somewhere, and it causes them to go nuts, that's life.

As for VLF, those frequencies are pretty much experimental, and let's face it, having a long enough antenna that can be placed high enough (at least 1/2 wavelength) is difficult if not impossible. If the antenna is less than 1/2 wavelength high, the signals radiate upwards to some degree instead of outwards like you would want it. As an example, I can communicate with stations worldwide on the 20 meter band (14 MHz), but I can only work stations in the surrounding states on 160 meters (1900 kHz) using the same antenna. It is only about 40 feet off the ground. Works OK on 20, but not so good on 160.

It seems to me that if the search coil is radiating "RF", you would be losing all the signal in ground reflection, and it wouldn't penetrate the ground very well, since you are swinging it less than 1/2 wavelength high for the frequencies used.

Plus, sound travels better through water (or "wet" ground) better than it does in air. RF is just the opposite of that. I also think that it is easier to get more energy into the ground at frequencies in the low kHz range, to induce those wonderful eddy currents into the targets we are after (usually :lol: )

It doesn't matter how much wire is in the search coil. RF is still emitted from the device.
Click to expand...

Maybe true, but having a antenna "matched" to the transmitter makes it radiate much more efficiently. You would think that the manufacturers of detectors would have optimized this relationship. It would relate to penetration and sensitivity.

Thanks. Enjoying the discussion.
Dave
 
Well everything's been said - almost. Remember that the guy behind the machine is just as important as the machine. Learning it, researching spots to hunt, etc. Good luck, Steve in so az
 
The Most important FREQENCY

...Is how "frequent" you get out there and swing your detector. Unfortunately there are some regulatory bodies that can severely limit your detectoring Frequency. The majority of these are Spousal in nature. The good news is some of them can be influenced by the "First Pick" rule.
 
steve in so az said:
Well everything's been said - almost. Remember that the guy behind the machine is just as important as the machine. Learning it, researching spots to hunt, etc. Good luck, Steve in so az
Click to expand...

Good evening Steve,

For sure true that is. In hunting today I found my first necklace. An interesting hit on the detector....it kept hunting around between high range, mid, and a few lows as I crossed over the target. Pinpointing showed a narrow but long target..but, since I was on top of sand on a volleyball court, I thought that it could be something interesting...not only the signal...but also the place..

Its funny how you can keep learning what the machine is telling you.

D
 
No all detectors are not the same.

If your only going to own one machine you need to match the detector to the area you will hunt most frequently. This is why so many own more than one detector.
 
There are many factors that go into a detectors ability to find metal targets. ALL detectors will find metal. As previously stated, some find gold better at higher frequencies and some find smaller targets or larger targets better. Frequancy is only one factor. Ground mineralization is the biggest enemy and some detectors do a better job at processing the information it recieves. To simply answer your question: All detectors will find all metals but some will find certain metals better.
FYI : The FCC regulates the OUTPUT of detectors to a max of 100 milliamps.
 
Laserfocusguy - Good going ! Even after 15 years with my detector I still learn things about it. steve in so az
 
FYI : The FCC regulates the OUTPUT of detectors to a max of 100 milliamps.[/QUOTE said:
I have to disagree Tony,

Here's what an engineer stated on the subject:

"The FCC does NOT impose a 100mW limit on detector "power". CFR 47 Part 15.209 specifies the transmit limits in terms of the electric field strength in microvolts per meter. Ferinstance, at 10kHz the limit is 240uV/m at a distance of 300 meters away.... metal detectors are not even close, by a long shot...
The reason that you can't just crank the power knob is (a) ground signal will getcha and (b) coil imbalances will getcha"

Tom
Click to expand...
 
My point was more that most detectors are probably very close as far as output power goes. That is to say, since I have never seen any detector claim to have more power rating than another, I think its safe to assume thats not a selling factor. The big difference seems to be in design. Features and the likes.
 
They are the same in purpose, but differ somewhat in ability.

savage_sultin said:
Hey all,
Thanks for the advice so far. I was wondering if all detectors pick up the same metals or are some specific to certain types?
Click to expand...
Without too much of the technical jargon, all hobby-based metal detectors re designed to find metal, plain and simple.

Some might appear to find only specific metals, such as a reference to a "gold nugget detector", but that actually describes a particular model's intended purpose based upon the operating frequency, and usually the fact that that model lacks any discrimination capability, and that it operates in an "all metal' detection mode.

Don't let names catch you up because a "relic hunting" detector does more than just find relics, a "coin hunting" detector finds more than just coins, and a "beach hunting" detector does NOT find a beach. :lol:

Operating frequency can play a small role in a detector's overall performance ability, but the search coil size and type must be factored in, as well as the control settings used, and certainly the ability of the circuitry to do its job.

Regardless of the operating frequency, some makes/models handle ground signal better than others. Some process out the target signal from the composite target/ground signal faster or slower than other models, and most hobby-use detectors are used in a motion-based Discriminate search mode, not All Metal.

Experienced operators often search in an All Metal mode and then use the Discriminate mode to help analyze a target, but most hobbyists search in a Disc. mode. Because of that, most folks have their detectors set to NOT respond to iron targets and some low-conductive targets like foil. Some adjust them higher so as to reject pull tabs.

So, while virtually all metal detectors (at least most detectors) have an operating mod that would permit them to find ALL metal targets, both ferrous and non-ferrous, they are usually operated in such a way that the operator has set them up to not signal a response to particular unwanted targets.

On the semi-technical side, as I understand it the FCC does regulate the amount of transmit power, but they are not able to operate at such limits due to the ground signal strength and other factors.

Operating frequency of most modern metal detectors is in the Very Low Frequency or Low Frequency range. The bulk operate in the VLF range from about 2 kHz to 30 kHz, with most designed to operate from about 5 kHz to 20 kHz.

THEORY suggests that there might be some advantages to designs in the lower or higher ends of that range, but there's more to it than just the operating frequency. As an example, I enjoy using my modified White's IDX Pro and it is my personal all-purpose detector. The more expensive and much more featured White's XLT operates at the same frequency (6.59 kHz) and uses the same search coils. While I like the XLT, over the years I have found deeper targets with an IDX Pro, had more accurate Target ID at depth with the IDX Pro, and definitely found more US 5? and low-conductive gold jewelry with the IDX Pro (or the non-metered model with the same circuitry).

The operating frequency and search coils were the same, same manufacturer, but a difference in how the circuitry is designed to work. In the end, they are both designed to find all metals, ferrous and non-ferrous, but the operator can control, to a degree, which metals they are able to have respond. ALL metals, in a true All Metal mode, or some metal targets based upon the discrimination used.

Monte
 
Good information! Other than I don't totally agree that frequency is a small factor.

Help me out here. If you have 2 frequencies say 1 at 3khz and one at say 50khz, would the 3khz have better ground penetration? All ground conditions being equal, since the 3khz has more a wider band than the 50khz, at the same amplitude wouldn't the the lower frequency travel farther?
 
Detector said:
Good information! Other than I don't totally agree that frequency is a small factor.

Help me out here. If you have 2 frequencies say 1 at 3khz and one at say 50khz, would the 3khz have better ground penetration? All ground conditions being equal, since the 3khz has more a wider band than the 50khz, at the same amplitude wouldn't the the lower frequency travel farther?
Click to expand...

This is an interesting question. I, too, would have thought that a lower frequency would penetrate the ground better, they're used for submarine communications after all, but the Rycom underground cable locator that I use at work seems to indicate otherwise. It will locate cables through two different means, one is a direct connection to the cable with a set of leads, and the locator set to 815HZ; this setting gives the most accurate locate, following bends and turns in the cable and going for a distance of around three miles. The other method involves setting the transmitter as close as possible over the buried cable and setting the unit to 82KHZ. In this mode, the locator will inject the 82KHZ signal onto the cable, and follow along the cable for approximately twenty-five feet. I've used the injection method to locate waterlines that were five to six feet deep, so it would appear that a higher frequency penetrates the ground better than a lower one, but this is just speculation on my part, since it could be that the lower frequency penetrates just as well, but won't follow along the cable. I don't know, but it's interresting.
 
Detector said:
Help me out here. If you have 2 frequencies say 1 at 3khz and one at say 50khz, would the 3khz have better ground penetration? All ground conditions being equal, since the 3khz has more a wider band than the 50khz, at the same amplitude wouldn't the the lower frequency travel farther?
Click to expand...

Not sure what you mean by a wider band. Do you mean bandwidth? Bandwidth generally describes the width of a signal when modulated. As an example (I am referring to analog signals here), your AM broadcast radio has less bandwidth than your FM higher-fidelity and stereo sound. Since the FM stereo hi-fi signal contains more information that needs to be decoded, it takes up more space in the spectrum to contain all that information. A television signal takes up even more space...it is 6 MHz wide (including the audio).

Let's backtrack a bit. What does a metal detector do, and how would we want to optimize it (in a basic technical sense...not lots of fancy indications and bar graphs and the like)..

The search coil basically radiates an electromagnetic field that rapidly switches polarity at some frequency. The coil is being fed with an AC voltage. The magnetic field then radiates in a conical shape below the coil. When it strikes a metal object, it induces currents in the metal, which create a magnetic field of their own. This is the field that is detected and processed by the processors in the detector.

In my mind, this means two things need to be optimal.
1) The frequency of the AC feeding the coil needs to be such that the ground looks "transparent" to both the transmitted and received signal. The ground absorbtion or reflection is the lowest possible. After all, we aren't detecting the ground, but objects in it.
2) The frequency used may have to be different for different types of ground conditions, due to their different absorbtion (and reflection) characteristics. (Mineralization)

I think that there is probably an "average for most soils and ground conditions" that has been experimented with trial-and-error over the years.
And with the automatic ground balancing that is on the detectors now, the frequency could be changed for best results on the fly.

This is an interesting question. I, too, would have thought that a lower frequency would penetrate the ground better, they're used for submarine communications after all,
Click to expand...

That is true, but you are talking about transmitters with a hundred kilowatts of output power feeding antennas that cover entire states. Not really comparable to metal detectors and their weak signal strengths. Plus, maybe those frequencies are best for communicating through the entire planet. (Low absorbtion & reflection)

I will close by describing an example of different frequencies behaving differently with some equipment I have worked with before. I work with industrial lasers, and in a past job the company used a type of laser called an excimer laser. It produced a beam of ultraviolet light (electromagnetic radiation) at a wavelength of 248 nanometers. The mirrors used with this laser were made of magnesium flouride. The mirror was fully reflective to the UV laser; yet you could see through it like it was a piece of glass. An example of how a material can be reflective at one wavelength (frequency), and transmissive at another.

I think in general the ground is similar in it's behaviour to the best frequency to use for metal detecting. It varies.
 
My understanding, from what I've read, is that lower frequencies in the VLF range provide for better ground penetration, whereas higher frequencies in the VLF range provide for better detection of small gold nuggets, but do not penetrate the ground as well as the lower frequencies. I've also read that ground mineralization is more of an issue with the higher frequencies.

I don't have any documented test results to cite, so please take this info for what it's worth. (Just my 2?.)
 
Detector said:
Good information! Other than I don't totally agree that frequency is a small factor.

Help me out here. If you have 2 frequencies say 1 at 3khz and one at say 50khz, would the 3khz have better ground penetration? All ground conditions being equal, since the 3khz has more a wider band than the 50khz, at the same amplitude wouldn't the the lower frequency travel farther?
Click to expand...
Frequency might play a larger or smaller factor, but it really depends on several other variables, such as ground mineralization, target metal type, coil used, and of course, how the electronics were designed to work.

"Book Theory" suggests a lower frequency might handle bad ground better and be a little hotter on higher-conductive targets, and that a higher frequency might be better on lower-conductive targets while not handling 'bad ground' quite as well.

I know that the DFX offers a two frequency selection, but I still get better all around performance from an XLT. The XLT operates at the same frequency as the XL Pro, yet the XL Pro will easily hunt deeper than the XLT. Both the XLT and XL Pro operate at the same frequency as the Classic III SL or IDX Pro, yet the latter two, lower-cost models generally get depth on par with or better than the XLT, often better than the dual frequency DFX, and they can hunt in trashier locations better due to their 2-filter, quick response circuitry.

Most of the hobbyists and dealers I know, in several states, who used an XLT and went to the DFX returned to their XLT within 1 to 5 months. Some went back to the XL Pro (6000 Pro XL) due to better depth, better Target ID and better overall performance.

Remember, we're not talking about high power, open-air transmission but hand-held devices that have to handle a ground signal as well as a target signal and reach several inches into the ground.

If comparing 3 kHz and 50 kHz, there is enough difference that, generally you would see a slight advantage in depth in favor of the 3 kHz model in bad ground .... IF the 3kHz model had circuitry that allowed the operator to ground balance (cancel or ignore) the ground better than the unit at 50 kHz.

But for the vast majority of models operating in the 7 kHz to 15 kHz range where most hobby detectors operate, frequency is a little less concern than all the rest of the electronic design.

Monte
 
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