TESORO GOLDEN SABRE

[Ropcsika]

Please help me! I build TGS. If you connect the tx coil it beeps continuously. What is the problem?

[Davor]

Actually shields are blocking E field pickup only (say, arcing, static etc.) and could be omitted entirely if symmetric (fully differential) operation is practical. There are "frame" ham radio antennas that also use shielding, and mostly because most of the noise is coupled from near environment via E field. These antennas have maximum in radial direction - remember, radio waves are formed orthogonal to each field. There is not much risk of picking up VLF transmissions with MD coils in the air either, because E field component that it would pick must be horizontal, and all such transmitters emit vertical E. The only way you could pick some transmission is by coupling with something in the ground, and there is no way shielding will help at all.

In short, MD's do their best in pouring as much energy in axial direction to metallic objects underground by magnetic coupling. Not waves. Waves form much, much ( ... much ... much...) farther.

[simonbaker]

Hi Andy,

schade, ich würde ja gerne mal in Deutsch antworten but many of the peoples wouldn't understand me.

We are detecting only the magnetic property and not EM waves. EM waves can propagate (travel) far, very far. Our coils are shielded and hence we aren't sensing electric fields (shielding blocks EM waves). We are sensing the magnetic field (changes). And we are emitting magnetic fields. We cannot emit EM waves (totally inefficient antenna and due to shielding).

Well, we have talked the 64 fold myth to death in the past. There must be some comments here at geotech.

Cheers,
Aziz

PS: Impoliteness not intended.

Doesn't Maxwell's equations say anytime you have a changing magnetic field you also must have an electric field associated with it? Can't block one only.

However, shields are probably effective at blocking slowly changing electric fields more effectively than slowly changing magnetic fields. Now, if your shield was a super-conductor, it would probably block the magnetic fields effectively also.

Oh well...

[der_fisherman]

To DSP or not to DSP

Hi Andy,
schade, ich würde ja gerne mal in Deutsch antworten but many of the peoples wouldn't understand me.
We are detecting only the magnetic property and not EM waves. EM waves can propagate (travel) far, very far. Our coils are shielded and hence we aren't sensing electric fields (shielding blocks EM waves). We are sensing the magnetic field (changes). And we are emitting magnetic fields. We cannot emit EM waves (totally inefficient antenna and due to shielding).
Well, we have talked the 64 fold myth to death in the past. There must be some comments here at geotech.
Cheers,
Aziz
PS: Impoliteness not intended.

I thank you for your answer and apology.

I do understand the 64 analogy with regards to a set Rx electronic and Rx coil.....I am sure its true, or better said, I accept it as being true.

But surely a better receiver electronic and/or Rx Coil (no matter what types of waves or energy we are receiving, though I must say that I would love to understand this technology better if possible), must give a better reception.

I know from personal experience that having a bad Rx system/setup reduces the distance at which I can detect metal. Simple fact!!

So the converse must also be true.....(I know that I am not alone here with such experiences either, c'mon Guys, put your hands up!!!)

Whether or not DSP is the way to go I cannot say, its well outside of my knowledge area, but I very happy to learn more from the experts here. Anything and everything is still VERY interesting....

I am also sure that if spacecraft signals from millions of miles away can be recovered from the very noisy deep space using DSP techniques, I am sure that we can do something to improve a metal detector working only over 40 cms or so!!! Hopefully with "lighter" bits and pieces than NASA needs!!!

regards
Andy

[simonbaker]

There may be some milage in doing some traditionally analogue stuff in dsp.

At the output of the detector, there could be a benefit in having quite a narow filter here.

If an analogue narrow band analogue filter was implemented its phase response or time to respond and pass signals thru could make them impractical. A FIR or IIR dsp filter would be a good bet here, as the bandwidth, roll off, phase response or time to respond (group delay) would be superb.

It would more likely mean a a new top down design, not something I am good at (dsp)

Steve

Good point, digital processing can be used to make some idealized filters that can be useful. I assume DSPs are handy for that, although we can do it also in a fast uProcessor. One type of useful filter is a bandpass with linear phase/frequency characteristic, giving a pure time delay with no wave shape distortion; could help keep the target pulse "fat" in the amplification section.

-SB

[Aziz]

I think those thoughts are valid for when the Rx is in a final form. To double the detection range you need a 64 fold increase in power.
But if you have a BETTER Rx, assuming the same Tx, you could effectively increase range over a simpler Rx.
If we assume for a moment (maybe incorrectly) that it is a "radio" type of signal, then we all know that a better receiver can receive weaker stations and improve the sound quality as well.
Is that not basically what is being proposed?
I am interested in learning more....its certainly very interesting and maybe we can achieve something.
So:-
WATCH THIS SPACE!
Regards
Andy
PS. You post came over as very rude as well......if you don't have any belief or want to know more, there are plenty of other great places to be......even on Geotech!! You may be correct in the end, but I personally (and a few others here) want to learn more, just in case......you certainly won't scare me off and I bet I am not alone either, (assuming that was your intention!! Was it?)

Hi Andy,

schade, ich würde ja gerne mal in Deutsch antworten but many of the peoples wouldn't understand me.

We are detecting only the magnetic property and not EM waves. EM waves can propagate (travel) far, very far. Our coils are shielded and hence we aren't sensing electric fields (shielding blocks EM waves). We are sensing the magnetic field (changes). And we are emitting magnetic fields. We cannot emit EM waves (totally inefficient antenna and due to shielding).

Well, we have talked the 64 fold myth to death in the past. There must be some comments here at geotech.

Cheers,
Aziz

PS: Impoliteness not intended.

[der_fisherman]

Hi all,

I thought, we know it better now!!!
WTF, ........
....... <cencored by ACTA> ........
<to open and read the message, STOP ACTA!>


We know, that the 64 fold power factor for doubling the detection distance applies in the far field distance region (distance >> coil radius R).
For distance regions around R and below, the required power factor for doubling the detection distance is less than the 64 fold.

When I want to double the detection distance from distance R to 2R (note R=coil radius), I only need 15.6 fold more transmit power.
For 2R -> 4R = 39 fold more transmit power.
For 0.5R -> R = 4.1 fold more transmit power.
For R/4 -> R/2 only 1.6 fold more transmit power.

You are encouraged to increase the coil size and push the transmit power to the ultimate levels.

Beam me up Scotty!

Aziz

I think those thoughts are valid for when the Rx is in a final form. To double the detection range you need a 64 fold increase in power.
But if you have a BETTER Rx, assuming the same Tx, you could effectively increase range over a simpler Rx.
If we assume for a moment (maybe incorrectly) that it is a "radio" type of signal, then we all know that a better receiver can receive weaker stations and improve the sound quality as well.
Is that not basically what is being proposed?
I am interested in learning more....its certainly very interesting and maybe we can achieve something.
So:-
WATCH THIS SPACE!
Regards
Andy
PS. You post came over as very rude as well......if you don't have any belief or want to know more, there are plenty of other great places to be......even on Geotech!! You may be correct in the end, but I personally (and a few others here) want to learn more, just in case......you certainly won't scare me off and I bet I am not alone either, (assuming that was your intention!! Was it?)

[golfnut]

There may be some milage in doing some traditionally analogue stuff in dsp.

At the output of the detector, there could be a benefit in having quite a narow filter here.

If an analogue narrow band analogue filter was implemented its phase response or time to respond and pass signals thru could make them impractical. A FIR or IIR dsp filter would be a good bet here, as the bandwidth, roll off, phase response or time to respond (group delay) would be superb.

It would more likely mean a a new top down design, not something I am good at (dsp)

Steve

[Aziz]

The 64 Fold Power Myth V2.0

Hi all,

I thought, we know it better now!!!
WTF, ........
....... <cencored by ACTA> ........
<to open and read the message, STOP ACTA!>


We know, that the 64 fold power factor for doubling the detection distance applies in the far field distance region (distance >> coil radius R).
For distance regions around R and below, the required power factor for doubling the detection distance is less than the 64 fold.

When I want to double the detection distance from distance R to 2R (note R=coil radius), I only need 15.6 fold more transmit power.
For 2R -> 4R = 39 fold more transmit power.
For 0.5R -> R = 4.1 fold more transmit power.
For R/4 -> R/2 only 1.6 fold more transmit power.

You are encouraged to increase the coil size and push the transmit power to the ultimate levels.

Beam me up Scotty!

Aziz

[simonbaker]

I worked for many years in the DSP arena and Digital Signal Processing can get extremely high return for the money. A matched filter that looks for a specific return signal or at least a signal that has close frequency components to the return signal can pick up weak signals out of noise. Finding signals in a SNR of 1 to 1000 was quite common using matched filters on a return signal. The problems arise in defining the noise spectrum and the signal spectrum. With the fast processor we have these days a DSP metal detector could likely tripple or quadruple depth.
Goldfinder

The Synchronous Detector in the TGSL is really a special case of a FFT at a single frequency -- the only frequency that matters in a VLF detector, the TX frequency. It doesn't need any fancy hardware -- just a switch!

I don't see how a DSP would be the right tool for a single frequency VLF MD. It is great if you are looking for unknown signals in noise, but the beauty of a Synchronous Detector is you know exactly the frequency of the signal you are looking for -- so a full FFT is really a waste.

It may have more use with a PI detector where you have a broad spectrum broadcast and you are looking for unknown responses and want to look at the frequency domain for various reasons. The time domain still may be best for actually detecting the presence of the target though.

Regards,

-SB

[xix]

I worked for many years in the DSP arena and Digital Signal Processing can get extremely high return for the money. A matched filter that looks for a specific return signal or at least a signal that has close frequency components to the return signal can pick up weak signals out of noise. Finding signals in a SNR of 1 to 1000 was quite common using matched filters on a return signal. The problems arise in defining the noise spectrum and the signal spectrum. With the fast processor we have these days a DSP metal detector could likely tripple or quadruple depth.
Goldfinder

Hi Goldfinger,
this sounds marvellous!! how can we start such type of project?
KR,
XiX

[simonbaker]

Dr Vel

these are good op amp reference texts

http://www.ti.com/lit/an/sboa092a/sboa092a.pdf

http://www.ti.com/lit/an/snla140a/snla140a.pdf

steve

Yes, nice, thanks!

[goldfinder]

Regarding DSP

I worked for many years in the DSP arena and Digital Signal Processing can get extremely high return for the money. A matched filter that looks for a specific return signal or at least a signal that has close frequency components to the return signal can pick up weak signals out of noise. Finding signals in a SNR of 1 to 1000 was quite common using matched filters on a return signal. The problems arise in defining the noise spectrum and the signal spectrum. With the fast processor we have these days a DSP metal detector could likely tripple or quadruple depth.
Goldfinder

[Dr Vel]

Thank you Steve those are very useful books.

[golfnut]

op amp cct reference

Dr Vel

these are good op amp reference texts

http://www.ti.com/lit/an/sboa092a/sboa092a.pdf

http://www.ti.com/lit/an/snla140a/snla140a.pdf

steve