field test unit no 001 "model T"

[Aziz]

Aziz, can we transpond those strong signal by some sort of modulation (e.g. phase modulation) from high coil resonance band to low sound card band?

You can move a bandwidth (frequency region) to any frequency region you want to have using a modulator. But if your measured bandwidth is limitted, you can't detect the higher bandwidth responses. TV, SAT and radio systems using this principle by translating the high frequency region into a low frequency region (or vice versa depending on the signal direction). This doesn't make sense in the MD technology. Forget this modulation type.

The other concept is using an integrator, which is integrating a "spectral response" depending on the time position and time duration and the frequency response of the integrator (note, it's a low-pass filter). You get a phase dependent DC voltage, which can be modulated into any frequency. The semi analog-digital system just maps some integrated DC voltages (samples) into the 48 kHz region (or even into the 20 kHz region if you want), which can easily be decoded by a slow ADC system.
Aziz

[WM6]

Now consider the TEM transmitter and a sound card processing at 48 kHz bandwidth. It works even, when the transmit energy is limitted to the 48 kHz bandwidth. And I have more bang to the targets instead of wasting a lot of TX energy.

Aziz

Aziz, can we transpond those strong signal by some sort of modulation (e.g. phase modulation) from high coil resonance band to low sound card band?

[Aziz]

Once again:

If you want to investigate the EM physics, the sound card based system is sufficient enough to make it. It doesn't matter, if you have low bandwidth. The physical effects occur in the low frequency region as well. And the principle remains the same and you can apply it for a wide band version.

You can use a semi analog-digital system with the sound card as well. The analog section in the front-end is sampling the high frequency response using S/H or integrator (most welcome) and converts it (the spectral energy) into a low frequency modulated signal (using a modulator), which can be decoded by the sound card by the software using the Tablet PC as a processing back-end platform.
You can imagine, that such a system can easily knock out an over-priced top detector. And the ground balance can be implemented in a very sophisticated algorithm/method.

You guys don't take me serious. I'm almost tired to tell you the same stuff over and over again.

Aziz

[Aziz]

Bandwidth limitting makes sense.

Consider, you have a TX transmitting a wide band pulse, let's say 10 Mhz bandwidth (ultra fast coil).
And you can detect only a bandwidth let's say 1 Mhz bandwidth.
Does it makes sense to transmit the other 9 Mhz bandwidth too?

No, not at all. You could move the "wasted" transmitted energy into the frequency region you take the measurements. And you have more bang to the targets.

Fortunately, the coil with it's parasitic capacitances and damping resistor forms a low-pass filter, which is limitting the reasonable frequency response into the 500kHz to approx. 1 MHz region. If you are not using (sampling) this frequency region, you are just wasting TX energy.

Now consider the TEM transmitter and a sound card processing at 48 kHz bandwidth. It works even, when the transmit energy is limitted to the 48 kHz bandwidth. And I have more bang to the targets instead of wasting a lot of TX energy.

Aziz

[Aziz]

Hi all,

may I add my comments?

Hey, don't forget, that the target response is also a wideband frequency response. The infamous target time constant TC is just saying, that in 1 TC time, the target signal response is decaying into the 1/e level (100% - 63.2% = 36.8%) related to the initial/reference response.

Even a short time constant targets produce a low frequency response but at low signal energy levels. Short TC targets have significant more response energy at high frequency region (just after the flyback period for a short duration of time: 0 < t < 1-2 TC).

The fact, that VLF detectors can also detect small targets is, that they accumulate the low signal response at much higher pulse frequency rates. Compare a PI at 1kHz and a VLF at 30 kHz. The VLF detector is accumulating the small signal response 30 times more.

That's the reason, why a low bandwidth will also work. But it might not be sensitive enough to small targets due to low spectral energy acquired (leaving the high frequency response). For chasing the fly****e targets, 1 MHz bandwidth is by far enough (not to say, it's an overkill).

Cheers,
Aziz

[Davor]

...The problem is WHAT IS NEEDED? Aziz says that audio frequencies are good enough (< 24KHz) Moodz is up in the MHz region ...

If you put underengineering aside, a whole point IS squeezing as much juice from as little lemon. The way I see it, moodz made a platform that will enable him to squeeze all the juice there is, and hopefully he'll find a more economic way of doing it in a process. Now, why would that matter? Say GPS! You may have mm precision location using nowadays GNSS technology using signals at 1575.42 MHz (L1) and at 1227.60 MHz (L2) with bandwidth of only (!) 10.23 MHz. So instead of going THz we have a perfectly good navigation system with much less that can fit into a wrist watch, and be purchased by ... just about anyone.
Carl mentioned target variation in 10Hz range, and moodz mentioned digital CRO as revealing tool for PI secrets. Well, cheap digital CRO's mostly do not employ as sexy ADC as 24bit@2MSPS, instead they use SAH and relay on periodicity of the signal at hand - which we have. 10Hz is very slow by any account.

So, how GPS using only 10.23 MHz bandwidth achieves spatial precision is a key as why <24kHz can be just enough. Exactly as VLF utilises phase granularity, every other system can use it as a compression tool for fine time granularity. If it takes a super sexy ADC and FPGA to reach there - fine.

[chudster]

yep I have seen the kickstarter.com site ...very interesting concept ...who is up for it ?

Well me for one. I think its an idea well worth exploring.

[chudster]

Carl,

Thanks for your recent multiple posts and input on sampling rate which makes sense.

I had a look at the topics and nothing leapt out as being appropriate. Where should such a discussion topic best be posted?

Chudster

[moodz]

I think you are 100% on target. If you look at past posts I put a stake in the ground that 1MSPS was likely to be a practical limit to the start of sampling. It makes sense when experimenting, as you are, to go higher than that.



It will not stop the patent being granted if the examiner is not aware of it- and you are right that they mainly seek prior art from patents. Companies though are happy to sit on their patent as a threat but drop like a hot potato or don't start action if there is a valid threat to that patent's validity from prior public disclosure. There is an old adage that a patent's value is never known until a court tests it. I suggested in a past post that if BW wanted ML to go away, finding prior art would be a great strategy. There is also an obligation on the patent holder to disclose any prior art it knows about and if a company employee read a forum post they are on shaky ground if they don't disclose that to a patent examiner if it was relevant.



But yet linux lives....



I don't doubt it. You would need to get the legals right and perhaps avoid some of the alleged grandstanding of the QED folks. An issue with any hardware though is getting funding to make it as business people want a return and could get scared by past patent action. BTW, have you seen www.kickstarter.com ?

yep I have seen the kickstarter.com site ...very interesting concept ...who is up for it ?

[Carl-NC]

So are you saying that a successful "open" detector project can be done ?

No doubt it can be done!

[Carl-NC]

IANAL but I am looking at putting together a project/ thread charter to mitigate the risk of a MD company doing to others as they have to BW and was discussing that with Philip for his thread. Despite the QED folks behaviour in rattling the bear's cage, some response to the action of ML needs to happen or we all run to our holes and they win by QED collateral damage.

Chudster

Folks are welcomed to open up discussions on this topic under a new thread.

[moodz]

Sorry if it is a tough question but:

What is the bandwidth needed to cover up to the smallest targets of interest (presumably small gold targets)?

Chudster

The bandwidth required is 1000 hurts at 10000 db ( dollar bills ) with at least 2 high power lawyers and a PA ( patent attorney ) section. And the small targets of interest are hobbyists like yourself.

[Carl-NC]

Sorry if it is a tough question but:

What is the bandwidth needed to cover up to the smallest targets of interest (presumably small gold targets)?

Depends on how you approach the design. A simple traditional PI running at a pulse rate of 1kHz only needs a 1kHz ADC sample rate to grab a single flyback sample. This can be used to detect a 500us-tau target, a 50us-tau target, or a 5us-tau target, depending on where the sample is taken. Keep in mind that the sample-to-sample signal variation is very slow, only 10's of Hz in BW.

If you also want to grab a ground sample, then the required sample rate depends on the spacing and ground sample width. This could suddenly jack the rate up to 100-200kHz. Then if you want to grab multiple samples for channelizing the responses you might want to grab data at 1-2us intervals, so now up to 1MHz. But even sampling at 1us, the signal BW is pretty low.

[chudster]

This accords with my experience. By the way I didn't want to cause offence, I meant crap design parameters. There is some good design evident, I just question the design parameters.




No offence taken ... I have already played with the lower speed sampling and for experimental purposes in PI & my advice is that they are too slow ....after all if you have a digital CRO do you run the sample rate at 100K ??? nope ... there is lots of interesting detail that is provided at the higher sample rates. If you think you know the "secrets of PI" then you can use the appropriate sampling rate as in this case it is being applied in context of what is known ... but .... as it has become obvious to me ... not everything is known about PI technology as some would have us believe ... so a little more bandwidth does not hurt for experimental purposes ... in this case it adds about $40 in cost.

I think you are 100% on target. If you look at past posts I put a stake in the ground that 1MSPS was likely to be a practical limit to the start of sampling. It makes sense when experimenting, as you are, to go higher than that.

"Patent examiners only read other patents for prior art ( and sometimes not all that thoroughly ) ..." .. quote from an actual patent examiner .... so dont hold your breath if you think a blog entry is public disclosure ... ( ie a collection of rambling text and diagrams VS a carefully worded and diagrammed technical specification comprising a patent application ). At the bare minimum it would have to be tested / examined and that costs money .... big money ... and for what ? no net gain if you are a hobbyist. If you are litigated against by one of these establishment player ... the real question is ... not if you can win .... but can you afford to lose ?

It will not stop the patent being granted if the examiner is not aware of it- and you are right that they mainly seek prior art from patents. Companies though are happy to sit on their patent as a threat but drop like a hot potato or don't start action if there is a valid threat to that patent's validity from prior public disclosure. There is an old adage that a patent's value is never known until a court tests it. I suggested in a past post that if BW wanted ML to go away, finding prior art would be a great strategy. There is also an obligation on the patent holder to disclose any prior art it knows about and if a company employee read a forum post they are on shaky ground if they don't disclose that to a patent examiner if it was relevant.

The same thing happened in software .. they tried / still are trying to nail Linux for years because it threatened the big monopolies .... so if you come up with an "open source" detector that threatens "the establishment" then dont expect you wont get a knock on the door.

But yet linux lives....

So are you saying that a successful "open" detector project can be done ?

I don't doubt it. You would need to get the legals right and perhaps avoid some of the alleged grandstanding of the QED folks. An issue with any hardware though is getting funding to make it as business people want a return and could get scared by past patent action. BTW, have you seen www.kickstarter.com ?

[moodz]

Hey Tinkerer,

Thanks for your response. Its helpful for the advancement of stuff with some real data to chew on.

In summary with a 2uS signal we need 1MSPS or higher to have a decent chance of detection or smaller targets. Moodz working at 2MSPS is 'overkill' but not unreasonable as its good to oversample (where is that antialiasing filter though Moodz). At 48KSPS, Aziz's soundcard seems OK for cannonballs with very long time constants (160uS) but not a tiny nugget.

Note we are talking about direct sampled solutions here. We can do all sorts of analog processing to have a half analog half digital solution (including integration) to mimic an analog detector with lower sample rates.

Chudster

FYI .. the antialiasing filter response can be seen in the spectral rolloff.