Frequency and Depth ??

[kando]

Now i hear that the higher frequency like 15 , 17 kHz ect will not go as deep as the lower ones like 3 or 7 kHz........... but Garrett and fisher and other ones with the higher frequency say they get as much depth as the lower ones average 8 inches could be 10 or 11 inches is that really possiable

 

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[Smudge]

To further add to the confusion, I have been told (and I'm no electrical engineer) that finding gold has less to do with the frequency and more to do with how the circuitry in the detector processes that frequency.

So in theory, you could have a 4 kHz machine that hits great on gold.

I'll leave it to someone smarter than me to explain that one.

 

[Keppy]

To further add to the confusion, I have been told (and I'm no electrical engineer) that finding gold has less to do with the frequency and more to do with how the circuitry in the detector processes that frequency.

So in theory, you could have a 4 kHz machine that hits great on gold.

I'll leave it to someone smarter than me to explain that one.

Could that be the detector makers are not giveing us the truth . Just so they can sell more & different models of detectors........... I would like to see some answers on this Question myself...................

 

[Smudge]

Keppy,

Whatever you do, don't change that avatar.

 

[Keppy]

Keppy,

Whatever you do, don't change that avatar.

Smudge.......... ****** I will keep it up for a while .....It is easy to look at...*********** SHE IS A PIRATE YOU KNOW..

 

[Smudge]

Shiver me timbers...

 

[earthmansurfer]

In general it was always pretty true that the lower frequency machines hit the higher conductors better (copper, silver) and the higher frequency machines hit the lower conductors better. Likewise, the lower frequencies seemed to go deeper than the higher frequencies.

Well, over the last few years machines are coming out that show this not to be as true, and for a variety of reasons. Machines like the T2 and F75 seem to load up on the power and somehow penetrate ground deeply, even with higher frequencies. (That said, I find deeper coins with my Omega than I ever did with my T2 and I had that machine for 3 years.) I am pretty sure that designers like Dave Johnson of the before mentioned machines are pulling out all the tricks in the book, such as playing with the timing in iron (recovery), up averaging around certain targets, etc.

Basically what is happening, from the engineers mouths, is that todays machines rely less on frequency and more on circuitry and processing. (I think as another poster said). Look at the AT Pro, 14kHz but hits deep and on all conductors. I am shocked at how deep my Omega gets copper and silver coins, easily within an inch of what an E-Trac normally gets, seen a few videos as well as read two many posts from people who compared or had both detectors.

 

[deepskyal]

Before multifrequency became a thing, my old White's used an average of 6. something to hit high and low conductors evenly. I dug a barber dime at almost 10" with it and iron down to 16". Now my Vision uses 3 frequency's that I can run simultaneously or just one.

I agree it's on the circuitry and processing, not frequency, that determines depth.

Al

 

[Ism]

I think the higher frequency units hit on smaller targets much better than low frequency.

 

[U.K. Brian]

The problem is that there's so many people knocking out books or posting on the forums either "borrowing" information from others and often not repeating it correctly, or in the right context, or just make assumptions.

I carried out lots of tests with large and small coins, even silver and gold bars.
Detectors used were a low frequency XP (4.6 kHz)
High frequency XP Goldmaxx (18 kHz)
Whites XLT (6.592 kHz)
and Minelab Sovereign (multifrequency, supposedly from 1.5 kHz up)

Now what they don't want you to know is that the amplitude of the same frequency between different detectors can be very different. So two detectors running the same frequency can give very different results.

Also the surface area of an object parallel to the bottom of the detectors coil is the predominate factor at any frequency.

Lower frequencies in effect add to the surface area of a target (giving more depth) as there is more penetration of the metal (possibly as much as 1/4" but little or no more). So to get extra depth from a low frequency the target has to be thick enough to allow a permeability depth gain.

Higher frequencies don't penetrate the metal to the same extent but this is counterbalanced by the ability to generate a greater signal on small/thin items because higher frequencies need less surface area to create a large signal.

My friend Sean summed things up well in saying that lower frequencies will give best depth but only on larger/thicker targets and will lose sensitivity on smaller targets, and that higher frequencies will perform deeper than lower frequencies for any target at any depth where there is little or no ground mineralisation.

So we should all buy BBS or FBS type detectors ? Unfortunately not. With a twelve and forteen inch coils a stack of silver bars (3 lb each) or a double stack with bars side by side gave a worse signal than the high frequency XP. Even worse if the stack of bars is added to by building upwards there's no depth increase and the signal in fact becomes worse.

All good fun !

 

[Keppy]

UK Brian.......... Are you saying that your test show that high freq. detectors will hit better & deeper .................Then the BBS & FBS multi freq. even with large coils on them ??....... I always said that the multi freq.detectors was not any deeper than the one freq.one's........ Could i be right.I always knew i was no matter what they put up on the forums.......

 

[U.K. Brian]

George Payne who invented S.P.D. ( motion ) detectors once published a list of the specific frequency at which an aspect of the discrimination calculation will peak. Silver at 0.8 kHz, copper at 2.7 khz, nickel at 17 kHz etc. This is ignoring ground effect which you haven't got much chance of doing in real life !

So multifrequency should be better but its suggested that MF units may not be able to linger on any one frequency long enough to take advantage of that frequency.
Once you have located a target you can then "linger" over it and improve I.D. but the initial depth of location will not be better than a one frequency machine especially if its been designed for a specific purpose.

Minelab were reported to the Advertising Standards agency in the U.K. and had to remove their advert that displayed single frequency machines with an arrow going a fraction of an inch down the page, twin frequency with their arrows going a bit deeper and then BBS/FBS going deeper again as it was misleading. Wet salt beaches are a different matter as the salt does require either extra frequencies or a pulse design to cope well.

 

[sniffer]

lower frequencies will travel farther through the air. if you have 2 frequencies, 1 low, 1 high, at the same amplitude or power, the lower frequency will travel farther and deeper

 

[earthmansurfer]

UK Brian

I never heard about varying amplitude, never crossed my mind but now that you mention it, it seems so obvious. I wonder if this would ever be an adjustable thing (on a machine like the V3i.) Probably too many variables to trust a user with.

There are two perspectives that I'm aware of regarding depth and multi frequencies. Detectors that transmit one at a time (Minelabs) and those that do multiple simultaneous (e.g. V3i). They say the V3i will go slightly less deep when using 3 frequencies compared to one as the transmit power (or something akin to that) is shared amongst the frequencies. A detector like a Minelab might go really deep, if it's trying different frequencies on the ground as a part of its processing and settling on the optimal one. Don't know if it is always trying different frequencies or if it checks every so often and settles on a another. I am not sure if anyone knows how the Minelabs really work, but they seem to hit silver deep (is what you mostly hear.)

It does seem as these machines get more and more complicated there is something to be said for simplicity as a machine like the V3i, in the wrong hands, will not get good depth at all as it's settings can hurt more than help when misadjusted. That is true to an extent on a simple detector too (e.g. - setting the sensitivity too high in mineralized or trashy ground.) What is interesting is a machine like the XP Deus over here in Europe (which is very adjustable, but not as much as the V3i) is still pretty much turn and go. They built a few safety features into the adjustments. Like when you touch one control it checks and adjusts depending on the other control. (I think it checks reactivity with another setting.)

 

[U.K. Brian]

I agree with you and think things started to go wrong with the DFX when the adjustments got just a little to dependant on a range of factors for many to get the best from the machine.

I liked the V3 (and love to fiddle/optimise) detectors but with both the DFX and V3 I could get really good performance after a degree of adjustment but living in a hilly area that is like a layer cake after moving 30 feet I would be on a different type of ground and need to re-adjust again.
Sweep speed of the coil is often not adjusted to suit the settings that are being used. Great that a Sovereign owner for several years can slow the speed down or the old time Spectrum user can speed things up to suit the habit they have got into but in general a setting option that would allow a degree of reactivity between the different settings would be a real improvement.

 

[Frankn]

Here it is pure and simple!
The power output determines the dept, period!!
The frequency effects which size target is detected best. ie,higher freq. smaller pickup target best.
The size of the coil only affects the pick up area. Note: some high end detectors will adjest power output for different coils.
Here's an interesting closing note. Subs. communicate with base using a frequency of 2Hz. Hope you enjoyed this electronic tour. Frank

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[U.K. Brian]

Pure and simple but out of date and all wrong (apart from submarines). You might be right on the submarine front for the U.S. but the biggest submarine fleets in the world operate on different frequencies.

 

[Frankn]

Brian, I was trying to get the basic electronic theories across without throwing in a lot of electronic hocus pocus. Most people that read the posts don't go into the advanced settings. Which statement don't you think is true?
The statement about the US sub frequency was meant to show an area on the frequency band not an exact frequency. It was meant to show that a low frequency can go around the world,underground. The antenna is so long it is buried in two states in the N.E. US. It can reach fully submerged subs anywhere in the world.

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[U.K. Brian]

In the U.K. when they changed the frequency for submarine comunication everyone had to send their Sovereigns back to Minelab for a re chip so they worked properly again. Luckily Minelab subsidised the cost. I don't remember hearing of U.S. machines having to be modified.

On the frequency front there's a couple of the U.S. and Bulgarian detector designers who say the old rules no longer apply. With careful coil and circuit design they can get high frequency machine sensitivity to small items from low frequency machines. The Golden Mask thats really hot on small hammered coins runs around the 8 kHz mark for instance.

While I agree that power output affects depth why do most detectors only put 6 or 8 volts through the coil ? My Nautilus can put 44 volts through and there's a beach machine that can run to 60+ volts. Can't think of anymore.

 

[Frankn]

Brian ,we both know that the voltage of the coil doesn't matter , it's the wattage output of the coil that counts.
I agree that signal processing is the thing now. It is getting so complicated that a company in the US is working on exact identification of the element detected. It works on the theory of frequency shift caused by molecular resonance which is unique to each element. The US gov. has already built and tested such a unit, but it uses nuclear material and is very big. I can't say any more about it.

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