New detecting method?

[g-sani]

http://iospress.metapress.com/content/q767074h6n070577/

I found this page accidently and I thought lets have a look because it is something coming from a University and I tried to read the concept but I couldn't.
Do you have to pay for it? This is what I understood.
May be I am wrong.

[Seden]

By typing in the title on Google, I found enough of the article here via Google Books that explains the tests with a schematic and graphs of the results. Wow, very interesting and nice to have a new idea for our hobby.

SWR take this very seriously.

Randy

[epitopios]

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

[J_Player]

Originally Posted by epitopios

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

Hi epitopios.

There is no circuit shematic showing components or values.
The designers from the Okayama University gave this vital information that explains the technique to discriminate metals:

[g-sani]

Originally Posted by epitopios

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

Well epitopios something like gold gun comes up to my mind.
I don't know, people involved in electronics can tell us more.
In Greece they say that 20Khz is allright for a receiver to be used for treasure hunting since there is transmition over here in this frequency.
The thing is you have to know what the meter is reading plus learning to read the audio signal is important as well.
VLF transmitters are not an easy subject when to be used for treasure hunting.
Many years back I used a AL718 and I was suprised to see that it was
responding in a known target(50kilos) of copper wire from 50mts away.
Then it was many VLF stations in use for Navy but now there are not.
I have it always in my mind as a problem to be solved in order to use my AL707 properly but I always hold back until I can see something serious as a solution.Okm sells 10Watts VLF Txs for big money.
I believe that 50W is a must for long range detection when using a receiver.
Any possible help in that is welcome.

[WM6]

Originally Posted by g-sani

I believe that 50W is a must for long range detection when using a receiver.


.

50W? Do you intend to sense gold from home on other hemisphere?

0.3W can be here far enough to reach way deeper than signals from former navy stations.

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

[Fred]

Originally Posted by WM6

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

Maybe this is why you need more power with inefficient antennas (ferrite), or gigantic military stations far away

[Seden]

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

[J_Player]

Originally Posted by Seden

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

Hi Randy,
What kind of ferrite, and what size do you recommend?
what size wire, and how many turns?

I am sure the oscillator can be adjusted to whatever inductance and response the coil assembly would produce.

Best wishes,
J_P

[mikebg]

Low power transmitter in catalog of Geonics Ltd.
The TX27 is a portable VLF transmitter supplying a VLF field for surveying with either the EM16
or the EM16/16R if remote broadcasts are weak, intermittent or poorly coupled with the target.
For EM16 surveys, the TX27 antenna consists of a long (typically 1 km) grounded wire.
PRIMARY FIELD SOURCE: Grounded wire or 500 x 500 m loop, current adjustable, 0 to 2 A
OPERATING FREQUENCY: 18.6 kHz
POWER SUPPLY: 120/220 V, 350 W motor generator
DIMENSIONS: Transmitter and loop; Shipping: 89 x 29 x 39 cm
Generator; Shipping: 50 x 27 x 36 cm
WEIGHTS: Transmitter and loop; Shipping: 32.5 kg
Generator; Shipping: 17 kg

[epitopios]

Originally Posted by Seden

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

οκ , but we will have a signal distortion or not ??

[J_Player]

Originally Posted by mikebg

Low power transmitter in catalog of Geonics Ltd.
The TX27 is a portable VLF transmitter supplying a VLF field for surveying with either the EM16
or the EM16/16R if remote broadcasts are weak, intermittent or poorly coupled with the target.
For EM16 surveys, the TX27 antenna consists of a long (typically 1 km) grounded wire.
PRIMARY FIELD SOURCE: Grounded wire or 500 x 500 m loop, current adjustable, 0 to 2 A
OPERATING FREQUENCY: 18.6 kHz
POWER SUPPLY: 120/220 V, 350 W motor generator
DIMENSIONS: Transmitter and loop; Shipping: 89 x 29 x 39 cm
Generator; Shipping: 50 x 27 x 36 cm
WEIGHTS: Transmitter and loop; Shipping: 32.5 kg
Generator; Shipping: 17 kg

Hi mikebg,
Geonics Ltd. has some very nice geophysical testing instruments in their catalog along with their logging systems. These could be very useful for mapping both shallow data and data from much deeper in the ground. I like the products they show. They have a particularly interesting arrangement of their PI metal detectors that use a focusing coil and digital data loggers that log multiple sample readings taken at various delays along the decay curve. These look like good tools to use for geological surveys.

I think epitopios is looking for a hand-held transmitter that tells him the direction where a metal object is buried at some distance, rather than a large loop placed on the ground. He is probably interested only in locating shallow metallic items (less than 5 m deep) without performing a survey, by simply holding a detector that will indicate which direction the metal is located.

Best wishes,
J_P

[g-sani]

Originally Posted by WM6

50W? Do you intend to sense gold from home on other hemisphere?

0.3W can be here far enough to reach way deeper than signals from former navy stations.

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

0.3W?
Why nobody did it then?
What I know is high power and very long aerials because of the longer wavelength.
If low power could be used then they would do it.Well as far as I know.
The thing is which one would be best for treasure hunting whith a receiver to go on target?
1. Sending the frequency into the ground using a probe?
2. Air transmision using a special aerial? What type of?

[g-sani]

Hi J_P
Don't you think that 5m depth is enough?
I think it is.
The best for me is a handheld device for a radius of 200 meters.
I know I am asking too much.

[WM6]

Originally Posted by epitopios

οκ , but we will have a signal distortion or not ??

Probably yes, but nothing bad if you use as TX very simple and cheap so called self-modulated transmitter. Find one schematic on web and as previous say you do not need more than 0.3W of power output signal to cover your actually search field and much much more. Simple try and you will see.

Antenna have to be resonate on selected VLF/ULF frequency and adjusted by impedance to transmitter output or on feeding cable (if you use cable to feed antenna it have to be adjusted by impedance on both side - at minimum reflected standing wave).

g-sani mentioned here good enough schematic for receiver, so called "gold gun" and Qiaozhi posted somewhere on forum. Basically it only have to be adapted to our TX frequency or vice versa and maybe need some mods. And again antenna is crucial part here too.

Main thing here, if electronic Tx and Rx stages was correctly build, come antenna. Antenna implementation can be different, regarding one needs and tendency, wound on ferrite rod too - even not so effective. Best solution for sure are wire antenna as pointed mikebg, but we need such gigantic antenna only for communication with other earth hemisphere and not for our limited search field. To cover our limited search field even ferrite antenna can be fully sufficient.

Practically two main type of antennas are applicable. Vertical stacked and circular radiated 1/4 wavelength antenna and directed frame (quad, triangle or circular) antenna. Vertical antenna can be put in the middle of our search field while directive antenna is usually placed on the edge of search field (higher-better, but especially vertical antenna have to be grounded).

Building of directive antenna on quad (circle or triangle) shape (1.5x1.5m) is well known from coil winding. We use coil calculator to determine Nr. of turns and inductance for given frequency and wire diameter. After about 100 windings we tighten coil, remove a bit of isolation from wire, measure inductance and recalculate coil data again. At the end antenna must resonate at Tx frequency. Then we need only to adjust antenna input to Tx output. Check this by put antenna at the virtually same position (nonmetallic carrier, radiating orientation and height) as it will be placed latter in search field.

Vertical stacked antenna can be build in such way: We use about 1.5m length rigid plastic tube with outer diameter of about 10cm and about 1.5m Alu tube OD 1cm. Then we use coil calculator and calculate coil for 4th upper harmonic of our Tx frequency (with coil inner diameter of 10 cm an length of 15cm). Mean if our Tx is working on 10kHz we calculate coil for 40kHz. Calculated Nr. of turns we divide per 15 which give our data of turns for each of 15 section windings. Then we wind 15 section of turns on plastic tube of about 9cm apart each other. One end of windings we connect to Alu tube which is stacked as extension of plastic tube other end to hot wire of Tx output. First (mean lower) of 15 winding sections have to be wounded with about 15 inter-windings connections for latter antenna tuning. This antenna is needed to be re-tuned on every search field cause of different grounding soil characteristic. Although once fitted on location comfortable for hunting, this antenna not suit best for less experienced.

[WM6]

Originally Posted by g-sani

0.3W?
Why nobody did it then?

Who is nobody, OKM?
Yes 0.3W is far enough.

Why OKM sell more Watts? Maybe for human vanity, you know, - "more power - more money" for OKM. And here ineffective "more power" is cheap for producer. But at the same time more power not mean more findings. Not at least by excessive power you can be quickly not only out of target but out of law too by strong widely disturbing interference. Not negligible too: by 50W of transmit power you need to bring with heavy bus accumulator to assure one day search.

This field is dedicated to art of sensitivity and harmony (resonance) not to question of power.

And probably they build antennas of very low quality - which are easy to produce but low effective antennas and try by excessive power to substitute this drawback, which is wrong approach but very profitable for producer of such things.

[g-sani]

Originally Posted by WM6

Who is nobody, OKM?
Yes 0.3W is far enough.

Why OKM sell more Watts? Maybe for human vanity, you know, - "more power more money" for OKM. And here ineffective "more power" is cheap for producer. But at the same time more power not mean more findings.

And probably they build antenna of very low quality - low effective antenna.

No I am not talking only about OKM WM6.
First I thought the ones they make feed the signal straight into the ground.Somebody else told me that you just put the aerial on the ground.This is how it looks in the photo anyway.Check the last line of the characteristics.Only 10 meters? Is it "maximal sphere of action" the effective range or something else?

Features of the Control Unit

Operating Temperature: 0 °C – 50 °C
Storage Temperature -20 °C – 60 °C
Air Humidity: 5 % – 75 %
Waterproof: No
Dimensions: 25H x 22W x 17D cm
Weight: about 7.4 kg
Frequency Range: 7 kHz - 60 kHz
Amplified Output Power: 10 W
Internal Battery: 24 V
Operating Time: (full charged battery) about 3 h
Charging Time: about 10 h
Maximal Sphere of Action: about 10 m

[WM6]

Originally Posted by g-sani

Check the last line of the characteristics.Only 10 meters? Is it "maximal sphere of action" the effective range or something else?

Frequency Range: 7 kHz - 60 kHz

Maximal Sphere of Action: about 10 m

Yes, low effective antenna, nothing else. Maybe without such antenna only by resistive end you can reach the same "Sphere of action". Those antenna act only as TX output load to prevent Tx damage not as real and effective VLF/ULF antenna..

It is understandable that no one can build effective resonate antenna for wide Tx range of 7Khz to 60kHz. Practically impossible.

And why one need such wide frequency range? This is not working on VLF/IB or BFO principle where are some differences in detecting between frequencies. Here not, except partially in the immediate vicinity of target, but we are asking for some remote detecting. Here you need only one frequency say between 10-30kHz and resonate Tx and Rx antennas to selected frequency and as good as possible directivity of Rx antenna.

[J_Player]

Originally Posted by g-sani;

Hi J_P
Don't you think that 5m depth is enough?
I think it is.
The best for me is a handheld device for a radius of 200 meters.
I know I am asking too much.

Yes,
I think less than 5 m deep is what most treasure hunters are usually looking for unless they suspect there is a worthwhile treasure deeper. Many treasure hunters would be happy to have a detector that can locate a buried treasure 2 m deep from a radius of 200m.

There are geophysical instruments that can locate metal things at this depth and also over 5 m. But these are not hand-held locators that you can put in your backpack and expect them to point the direction of a buried treasure. They are used to perform surveys of an area that is plotted so the data shown on maps can be analyzed by a geologist to determine what is under the ground. VLF signals that geologists use are transmitted from large VLF beacons all over the world. They receive these beacon signals between 1-30 KHz, and can collect data up to 25 m deep in the ground, and sometimes deeper when holding a loop receiver antenna in their hand to pick up the distant transmitter signal.

But if you are looking for shallow anomalies at less than 5 meters, then you can raise the frequency up to 150KHz for better resolution in your survey. The large military VLF transmitters do not use ground probes for a transmitter antenna. They have a large arrays of antennas in the air. Geologists use ground probes to measure the ground resistivity and induced polarization, which are electrical measurements, not RF. The idea that you can get efficient wave propagation in the ground by using ground probes does not sound correct to me.

In order to use a small portable transmitter, I agree with WM6, that a small air core loop will probably work the best. From what I can see WM6 is very knowledgeable in how to make an efficient VLF transmitter, and probably understands the near field propagation and ground absorption better than someone who tells you it can be done best with putting probes in the ground.

Best wishes,
J_P

[J_Player]

Originally Posted by g-sani;

Hi J_P
Don't you think that 5m depth is enough?
I think it is.
The best for me is a handheld device for a radius of 200 meters.
I know I am asking too much.

Yes,
I think less than 5 m deep is what most treasure hunters are usually looking for unless they suspect there is a worthwhile treasure deeper. Many treasure hunters would be happy to have a detector that can locate a buried treasure 2 m deep from a radius of 200m.

There are geophysical instruments that can locate metal things at this depth and also over 5 m. But these are not hand-held locators that you can put in your backpack and expect them to point the direction of a buried treasure. They are used to perform surveys of an area that is plotted so the data shown on maps can be analyzed by a geologist to determine what is under the ground. VLF signals that geologists use are transmitted from large VLF beacons all over the world. They receive these beacon signals between 1-30 KHz, and can collect data up to 25 m deep in the ground, and sometimes deeper.

But if you are looking for shallow anomalies at less than 5 meters, then you can raise the frequency up to 150KHz for better resolution in your survey.
The large VLF transmitters do not use ground probes for a transmitter antenna. They have a large arrays of antennas in the air. Geologists use ground probes to measure the ground resistivity and induced polarization, which are electrical measurements, not RF. The idea that you can get efficient wave propagation in the ground by using ground probes does not sound correct to me. When geologists do want to transmit their own VLF signal, they lay a cable down on the ground in the form of a large loop maybe 1km diameter, then use their hand-held receivers to survey the area around the loop.

In order to use a small portable transmitter, I agree with WM6, that a small air core loop will probably work the best. From what I can see WM6 is very knowledgeable in how to make an efficient VLF transmitter, and probably understands the near field propagation and ground absorption better than someone who tells you it can be done best with putting probes in the ground.

Best wishes,
J_P

[g-sani]

Thank you J_P, I can undrestand that WM6 knows better the subject.
So what do you think it is best to use whith my gold gun?
Is it a necessity to transmit in exactly the same frequency as we receive?
Do you know if there is anything ready to be used in the market?

[g-sani]

Originally Posted by WM6

Yes, low effective antenna, nothing else. Maybe without such antenna only by resistive end you can reach the same "Sphere of action". Those antenna act only as TX output load to prevent Tx damage not as real and effective VLF/ULF antenna..

It is understandable that no one can build effective resonate antenna for wide Tx range of 7Khz to 60kHz. Practically impossible.

And why one need such wide frequency range? This is not working on VLF/IB or BFO principle where are some differences in detecting between frequencies. Here not, except partially in the immediate vicinity of target, but we are asking for some remote detecting. Here you need only one frequency say between 10-30kHz and resonate Tx and Rx antennas to selected frequency and as good as possible directivity of Rx antenna.

I know that my gold gun AL707 receives in 19.6khz and also in another two lower freqs but how can I accurately measure the frequency myself WM6?
I think I have to verify the receiving frequencies myself first before I will see about the transmiter.
Thanks for helping.

[J_Player]

Originally Posted by g-sani

Thank you J_P, I can undrestand that WM6 knows better the subject.
So what do you think it is best to use whith my gold gun?
Is it a necessity to transmit in exactly the same frequency as we receive?
Do you know if there is anything ready to be used in the market?

Hi g-sani,
I have never used any hand-held detector on the market that was able to locate buried metals for me at a long range more than about 1/2 meter, or maybe up to 2 meters for very large metal things when using a VLF loop. I only hear stories that other people say there are locators that can find buried metals at long range.

I have no way to know if a Gold Gun is best for you to use. If you can find a gold gun, then you could check to see if it is locating buried metals for you. If you find it helps you to find buried treasure, then you will know whether you should use it or not.

From what I understand, the gold gun is a receiver without a transmitter. I have no idea of what RF or electronic principle it uses to locate buried metal. But if it is only receiving RF, then it could be looking for the strongest signal strength, or it could be looking for some specific kind of modulation or interference at the frequency it is tuned to. I have no way of knowing because I don't know what the circuit electronics are designed to detect.

One thing I can tell you that if it is an RF receiver with added signal processing circuitry and no transmitter, then it is designed to receive RF signals from a distance, not from a transmitter at close distance from the receiver. If you were use a small transmitter at your hunting site, then the signal coming from this transmitter will be broadcasting RF in the near field, whose propagation properties are not the same as transmitters far in the distance. You will find that the field strength and radiated power pattern does not follow the math formulas that are used to determine what that signal will be if it came from a distant transmitter. But at least any modulation you send from a nearby transmitter will be preserved in the near field area.

If you want to know more about how to actually build a transmitter and receiver, I would recommend that WM6 is very knowledgeable about this, and probably has more experience and knowledge than most people in this forum.

Best wishes,
J_P

[g-sani]

Hi J_P
Once many years back a friend of mine gave me a gold gun al718 for a month to see if it can detect anything or not.
There was a single page inside its box roughly explaining its operation.
All I paid attention then it was a part saying that if the pistol like detector was pointed to a precious burried target goes silent.
I discovered some guns from the 2nd world war once from about 50 meters and some other time it was 5 or 6 bullets spread close to each other but only 15cm deep.I was surprised to see that it was easy to go on target.
The gold gun has a digital voltmeter giving different readings as you sweep it from side to side apart from the amplified audio signal in the speaker.
I didn't use it many times to say the truth but I could tell whith the experience I had those days that this pistol could detect something.
This is how and why I got my goldgun later on from a shop that was closing down in States.I bought it for much less money than what Accurate Locators used to sell it.
I discovered later on that probably this type of lrl doesn't work any more since most of the VLF stations arround Greece closed down.
Some other users here in Greece say that there are some emmisions in certain days but thats not a solution for me.
Even accurate locators made a Tx later and started selling it again until it was for some reason discontinued.
So I am in position now looking for a Tx to duplicate the emf fields of the old days that don't exist now.
But the truth is I always leave it behind J_P because I can not reach to a right conclusion of what is best to do.

I can put photos down of the cct or the pistol itself but I think somebody put some already in the forum under some other thread.

[WM6]

Originally Posted by g-sani

I know that my gold gun AL707 receives in 19.6khz and also in another two lower freqs but how can I accurately measure the frequency myself WM6?
I think I have to verify the receiving frequencies myself first before I will see about the transmiter.

I don't know what of instruments do you have in your lab.

If you start from "Gold gun" which is real for you, you need first to measure all of (as you say) three frequencies of your AL707. Do not believe to producers data it may vary, but because of ferrite antenna ("widest" Q) real data can be inside of acceptable tolerances.

There are some way to measure antenna resonance but first rule have to be that we may not to over-burden input LC circuit by direct measure instrument connection in a way to change his resonate frequency.

So we will try to measure without to over-lasting antenna circuit. Maybe you have or can lent some sort of reliable audio signal generator or signal generator for general use. If so, you first wind your testing transmit antenna from about 10 turns (1mm Cul) 10cm in diameter (or 10 turns on ferrite rods) and connect such testing antenna together with serial connected 1k pot (trim to middle position) to generator output. Put generator output on unloaded (max peak to peak output) square signal (typically 15vpp). Now you have your testing measurement transmitter ready.

Put your AL707 "ON" and approximate it to test antenna at about 20cm. Now you start to gradually change generator frequency from 0Hz to about 35kHz and watch for react from AL707 speaker or led. If you catch signal, try to establish his maximum. Frequency at which signal reach his peak is resonate frequency of selected frequency position of your AL707. Try the same way to establish other two frequency. In case of strongest signal from receivers speaker you can use attenuator on signal generator to get weak signal or put AL707 so apart from TX antenna to get weak signal from speaker. By weak signal we can more accurate establish peak and by this more accurate resonate frequency too.

In case of no signal from AL707 you can first regulate serial pot to lower resistivity of about 100E, more approximate test antenna to AL707 and at the end try to open it and measure signal at amplification stage by mV-meter or scope. To prevent possible damage hope that this would not be needed.

After you establish all three of antenna circuit resonate frequencies your next step is transmitter adopted to middle of three frequencies (or on one of his lower harmonics).

Here may you suggest to buy very usable testing instrument Portable frequency counter with possible use as field strength meter. You can search for it on eBay under name "GE FC-1 Portable Frequency Counter 10Hz - 2.6GHz". Usable to detect in-depended of transmitter and receiver resonate frequency of TX antenna and cheap.