New detecting method?

[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?

[J_Player]

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

[J_Player]

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

[WM6]

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.

[g-sani]

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]

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.

[WM6]

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.

[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.

[g-sani]

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?

[J_Player]

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

[epitopios]

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 ??

[mikebg]

TX of Geonics

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

[J_Player]

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

[Seden]

New detecting method?

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

[Fred]

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