Regarding Frequencies

[TC]

I can't seem to find much discussion on the frequencies the different detectors use and the advantages/disadvantages of multiple/single freq detectors. Maybe a chart on conductivity versus frequency if anyone has one. Most lower priced machines work in only frequency while others have 7, 18 on up to 28 freq's.

 

[Cherry Picker]

Good question. I've often wondered why you never hear much about one detector being more sensitive to items than another. For example the Explorer II has 28 frequencies and the DFX only has 2. Now you would think you would hear a lot about the EXP II being far more sensitive than the DFX, but you never do.

The way I understand it is the lower the frequency the deeper, and the higher the frequency the more sensitive to small targets. DFX only has 2 because they found the 2 most usable frequencies(3khz and 15khz) are sufficient.

It still is a bit confusing because you'd think 28 would be better than 2 but you just never hear much about it.

 

[TC]

And the ACE-250 splits the difference at 7.2khz. I just believe that the freq of a detector plays a larger role when choosing the right detector, factoring in soil and surrounding conditons. The X-Terra 50 offers only a single freq but varies it with the coil for the depth and size range.

I've been looking at both the explorer and the X-Terra (amongst a couple others), and without the 'swing time' find that I think the freq range could make a huge difference. Or am I making too big a fuss about it?

 

[~Alan~]

I believe that even the multi-frequency detectors, only use one frequency at a time ?
Much is made of machines with multi-frequency capability, I'm not convinced that this is the be all, and end all, of detector technology.

 

[Schrecky]

The DFX runs @ 3khz and 15khz. You can run them both at the same time in Best Data mode or Correlate Mode. You can also select either of them individually to hunt with. You are right, the conditions; mineralization reading, mineralization strength, EMI, desired target, trash factors all enter into the decision on which frequency setup to run with. 3khz is more sensitive to high VDI targets (pennies, dimes, quarters, halves, etc) and 15khz is more sensitive to lower VDI targets (nickles, jewelry, etc). Using just one frequency offers the ability to notch out trash with more percision than using both at the same time. Running them both at the same time has many advantages but can loose a little bit of depth. Whites selected these two frequencies because they are the most sensitive frequencies for the range of targets above. If you had more frequencies available would that mean that your detectore would be more senstive in areas outside of the targets ranges above? I'm not sure I'd want it to be more sensitive in other areas, trash for the most part.

I've only been MD'ing for 6 months and the DFX is the only detector I have owned so I can't comment on the other detector.

 

[Cherry Picker]

Maybe someone can answer these questions I've had about these two titans.

[28 vs 2] Why does Minelab not say the Exp II uses 28 frequencies SIMULTANEOUSLY? All I've seen advertised is "2 dimensional discrimination." This can be read to mean, like the DFX, it only uses 2 frequencies.

An interesting bit of information about metal detector frequencies is that, from what I've read, any frequency above 20khz is a waste except for air tests. While the higher the frequency the more sensitive to say gold, above 20khz the minerals in the ground react the same as gold making it useless.

[Depth] From users of both the DFX and Exp II the Exp II clearly seems to have more depth, but if I'm reading the, as factory ship, info correctly the Exp II has a 10.5" coil and the DFX a 9" coil. It used to be suggested that the general depth a detector can go is roughly the size of its coil all conditions considered.

My questions is, is the depth advantage of the Exp II from a larger factory coil, the 1.5khz vs 3khz or better electronics? This is important because if its simply due to a larger coil then simply buying a larger coil puts the DFX as the superior machine. If the depth advantage is the 1.5khz vs 3khz, then this advantage would be limited buy target type.

Also, I don't seem to be able to find any info on the processor of detectors. For me this would be the most important bit of information. How fast is the processor. Response time can make a detector. 100 frequencies is irrelevant if the processor is slow at processing the incoming information.

 

[WThesing]

Let me try to give an explanation on the Explorer II, the way I understand it. ( I could be wrong on some of the details)

The machine does not use all 28 frequencies at a time. They are pulsed by the onboard computer at a very high speed. I'm not sure whether it is done one at a time or some multiple, but they are all used over and over by switching on and off at mindboggling speed. This is part of the reason that the machine has a slower recovery speed than most. Using all of the data from all of the frequncies, the chip must also keep the information stream clear, temporarily restrict channels producing excess noise if present, then process the info for identification. I believe that when a target is present, the computer modifies the transmission through each frequency in order to get the best I.D. profile. I am by no mens a rocket scientist, but have an above average understanding as to how things like this work. There are discussion threads on the Findmall forum, which quite honestly bore the hell outta me........I'd rather be finding stuff than talking about the nuances that allowed it. That's why I bought a good machine, so that I would have the right tools when needed. So far I have NO COMPLAINTS!!!!!

Bill

 

[WThesing]

I seemed to have missed something.

When the target is deeper, the processor modifies which frequencies become more "primary" according to the info in the data stream. This info is updated to again provide the clearest profile.

I have personally recovered BB size targets in a cornfield at over 15" depths. I have also recovered coins on a beach at 20" plus. The damn thing just works, and works great. I understand that there are aftermarket coils that will boost performance, but right now, I can't see a need for them considering all the different types of hunting I do.

Lastly, given the size of the circutry today, what would be the possibility of a machine using more than one processor, each assigned to different areas of function, then all of the gleaned data compiled by a master processor???? This could be with any mid to high level machine.

 

[Cherry Picker]

Multi-processor is probably in the future if not on the bench.

One concept I've always had is an all-metal-mode detector that discriminates by notching/filtering a response on its frequency sorta like tone ID.

We all know all metal mode is the deepest and being a ultra-slow/non-motion mode it makes response time less of a factor, already in pinpoint mode and saves the arm wear and tear from constant whipping the coil. If they could use the idea of only sending the accepted frequencies to the speaker/head phones it should make for a great all purpose machine.

Or sound technology. I played guitar for years in many different bands and also took care of the sound system. I used a pinknoise generator to adjust the system according to each rooms acoustics. Why can't the same technology be used in a metal detector? transmit sound waves in the ground and process the reflected signal.

A feature I'd like to see, once the military opens it up, is the use of GPS on metal detectors. Imagine pinpointing a signal within centimeters for reference. Being able to return and resume at the exact spot you left off. Knowing precise depths.

 

[~Alan~]

A feature I'd like to see, once the military opens it up, is the use of GPS on metal detectors. Imagine pinpointing a signal within centimeters for reference. Being able to return and resume at the exact spot you left off. Knowing precise depths.

Yes that would be a good feature. I also wonder why no manufacturer has yet managed to put a clock on a display ?
I've stuck a watch on my Hawkeye using a piece of velcro.

.

 

[WThesing]

I used to train SAR crews for the Coast Guard. I am very familiar with the function of GPS in both civilian and military format. The accuracy within centimeters does not yet exist at least with the satellites of today. With weapon guidance we are looking at 4 - 6ft. The weapon destruct radius far exceeds that. Accuracy with civilian equipment WAAS enabled is 3 - 5 meters at best.

I think the ultimate will be an MD with integrated cell phone, DVD player, cupholder, wet nap dispenser, and onboard computer to ID the finds by internet access as well as access this forum!!!!

 

[nfunk]

I believe GPS systems using post processing and real time Kinematic GPS is capable of sub centimeter accuracy.

 

[bdoubled]

Multifrequency may not be the future of metal detecting, but it is definitely the PATENT of Minelab. White's licensed it from them to make their DFX. I'm no expert, but from what I've read and experienced, machines that operate at lower frequencies (about 4 kHz) may go deeper, but may not see small objects and may have a slower recovery time. Higher frequency machines (about 18 kHz) may not go quite as deep, but they see smaller targets and have a faster recovery time. Perhaps that's why many detector manufacturers design machines that operate between 8 and 15 kHz -- to strike a happy medium.

 

[TC]

Makes much more sense to me now why the so scattered sets of frequencies amongst the different manufactures. I figured as much but do enjoy the input of others. Helps in choosing another detector too. Thanks all.

 

[Brian]

Multi frequency metal detection was used by Westinghouse first so give the credit to the U.S.
Minelab applied multifrequency to a hand held hobby machine.
You don't really have the claimed frequencies. Harmonics are used, apply that to a P.I. and they have around 99 frequencies. Whites have two frequencies, Minelab three. What can be transmitted is not what is received. But credit where credit is due it does work.
I don't feel the Explorer processor is up to the job just yet. Perhaps with the Mk 3 version.
If the Explorer and the DFX had the same size coils then the Minelab still has a slight edge. I also find that the DFX (land) performance is better when a single frequency is used. Which one depends on the size of the item and the amount of ground mineralisation.
Re modern advances such as the X-Terra where a change of coil gives a different frequency I don't see what was was wrong with the later Compass Challengers where you kept the same coil and just flicked a switch on the control box. It gave the opportunity to see what effect a different frequency had on a target instantly.

 

[bdoubled]

Quite right on the patent, Brian. Here's it is: US 3,686,564. I think some people get too hung up on the specs and neglect the user technique. No matter what the detector itself can do, it won't get the finds if its user doesn't fully understand it. Like any specialized tool, there are different tools for different uses.

 

[Willy]

Actually, I wonder who was first with the multifrequecy bit 'cause Fisher has had the CZ's out for a coon's age. When it comes to frequencies and such there almost seems to be more BS out ther than actual facts. I've had a number of multifrequecy detectors and lods of single frequecy ones and, except for special situations (alkali), have found no depth advantage to be found with M.Freq. machines. I've also found that the actual frequecy of a detector, while possibly conferring greater sensitivity with higher frequency, has to be matched to preamp gain and stable operation. A lower frequency detector can quite possibly have greater sensitivity to small/low conductors if it has a great amount of gain and great groungd handling. That's why the MXT at abt 14 Khz can rival the higher freq. gold detectors. A lot of coin machines seem to be detuned in order to make them run smoother. They often have extra filtering in the disc. circuits which, while making for a more pleasant detecting experience, tends too knock out some targets. This can be seen with the MXT coin mode vs. relic mode. The relic mode has extra filtering applied and sounds much smoother than the coin mode. Another example is the QXT. This detector allows a person to turn off the noise reduction circuitry in disc. mode, making for a deeper/more sensitive detector which pops and crackles. ..Willy.

 

[Brian]

I had the original Sovereign (where you could turn the iron mask off) a good few years before Fisher came out with the CZ 6. As with the DFX they had to get a licence from Minelab.
C-Scope, the U.K.'s biggest detector manufacture, still advertise that with the exception of a few exceptional areas (and the wet sand) that there is no advantage to twin/multi-frequency over single. Meanwhile Minelab were made to withdraw their adds that showed one frequency going part way down the advert, twin a bit further and multi further again.
Though I have twin and multifrequency detectors its rarely that I can't find a single frequency machine that has the edge inland so I guess I agree with you.

 

[Willy]

I dunno, just checked the Lost Treasure website under field tests and both the original Sov. and the CZ6 came out in the same year (if one goes by the dates on the tests).. 1992. ...Willy.