field test unit no 001 "model T"

[Aziz]

In PI, it does make sense. The BW of the TX pulse determines how hard the target gets kicked. The harder you kick it, the stronger the response. Once the target has been kicked, it is true that you don't need to maintain all that BW through the receiver. In fact, you can direct sample with only 100Hz of BW.

Hard kick (high dI/dt) = high frequency response = energy efficient kick
Yes, that's pretty fine.

Remember, the whole TX spectral energy is spread over from the TX pulse frequency up to the upper limit. That's a large bandwidth.
Now imagine, when someone is using due to limitations only 100 kHz BW of the let's say 800 kHz BW. 700 kHz BW TX spectral energy is wasted in this case. The energy could be used elsewhere.
Aziz

[Tinkerer]

Not true. The preamp can provide a better SNR than you can get with an ADC alone, unless the ADC has a built-in LNA. In direct sampled radios there is always a LNA in front of the ADC. Also, a lot of these high-res ADCs are rather picky about how they are driven, and often need a preamp with a particular matching network to minimize sampling kickback. You sure don't want the sampling kickback to see a coil.

Also, an integrator establishes a "channel" that limits your processing, i.e., you need a separate integrator for every unique portion of the response you want to process, but a preamp alone does not limit processing.

I agree. I as trying to get a definition of "direct sampling"

In my experiments with traditional PI, I observed that the capture of very short TC targets can be enhanced by integrating on the pramp level. Although the peak amplitude gets diluted by the integration, the signal TC gets extended. The key word that needs to be added to integration is the integration time.

Tinkerer

[Tinkerer]

Don't talk about GB with me then, Aziz. Talk to the members of this forum and explain where, with a PI, the X component is coming from for Ground Balance.

Just in case this was a genuine question, I will give a genuine answer.

With traditional PI, you can find the X response at any time that you have current flowing in the TX coil. This may be during the TX ON time as well as during the Flyback decay time.

Tinkerer

[Davor]

Hard kick (high dI/dt) = high frequency response = energy efficient kick

I think this is just partially true - the frequency part will remain the same in a given system, regardless of the peak voltage you obtain with the kick.
The way I see PI systems is a bit of a contradiction. In one hand it is proclaimed to be resilient against the fast ground and reactive responses, sea water and whatnot (near 90° responses in VLF) by virtue of delayed sampling, but in the other hand as the same principle also hurts detection of small gold a "somewhat" faster response is chased after. Being good and having fun at the same time in a way. Kinky and saintly. A contradiction.

Obtaining the faster sampling is actually brain-dead simple: just reduce the kick. Nothing is going to happen with the frequency response, exponential fall is going to be the very same.

[Davor]

The key word that needs to be added to integration is the integration time.

Too bad input signal is not a linear decay so that this makes complete sense. It could be with a log amp though

[Tinkerer]

Too bad input signal is not a linear decay so that this makes complete sense. It could be with a log amp though

Right, with even a crude log function in the preamp, I could read a 10usTC target still after 100us.

Tinkerer

[Davor]

I so love when you speak dirty

[Carl-NC]

I agree. I as trying to get a definition of "direct sampling"

"Direct sampling" traditionally means directly sampling the carrier signal, with no prior demodulation. Amplification & filtering are fine, and normally done. There is also IF sampling and baseband sampling. Most detectors use baseband sampling. Minelab X-Terras and White's Prizm 6T use direct sampling. One of the projects in my book is a direct sampling PI.

In my experiments with traditional PI, I observed that the capture of very short TC targets can be enhanced by integrating on the pramp level. Although the peak amplitude gets diluted by the integration, the signal TC gets extended. The key word that needs to be added to integration is the integration time.

Interesting isn't it? Putting a ~5us pole on the preamp pushes fast target responses out in time so you can see them. I used this trick in my security walk-through PI design. It does, however, weaken responses, which is to be expected.

- Carl

[UrbanFox]

as if you have any idea
Why does every troll have to pose as a stuffy professor, or as a nagging woman :duh:

Hi Davor, could you please explain for me where the X component is coming from to do PI Ground Balance??
What is trolling about the question?? Aziz made a statement about X and R components being used for GB, and as the thread is focused around PI then I feel the question is appropriate.

[chudster]

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

Note that the thread has been opened at:

http://www.geotech1.com/forums/showt...roject-Charter

Chudster

[UrbanFox]

Just in case this was a genuine question, I will give a genuine answer.

With traditional PI, you can find the X response at any time that you have current flowing in the TX coil. This may be during the TX ON time as well as during the Flyback decay time.

Tinkerer

Thanks Tinkerer. I am looking at a previous post...

http://www.geotech1.com/forums/showt...003#post158003

Where it was stated...

"But the ground balance can be implemented (by separating X and R) and the relation of X/R (or vice versa) gives a good indication to discriminate iron/non-iron targets. It might work for most conditions. But can fool you too"

My understanding is that the statement can be applied to VLF, but GB with PI will not directly use X component. Am I incorrect?

[moodz]

Thanks Tinkerer. I am looking at a previous post...

http://www.geotech1.com/forums/showt...003#post158003

Where it was stated...

"But the ground balance can be implemented (by separating X and R) and the relation of X/R (or vice versa) gives a good indication to discriminate iron/non-iron targets. It might work for most conditions. But can fool you too"

My understanding is that the statement can be applied to VLF, but GB with PI will not directly use X component. Am I incorrect?

You are incorrect.

[UrbanFox]

You are incorrect.

Thanks for that detailed explanation, Moodz. Is that the answer you give when you haven't got an answer??

[moodz]

Thanks for that detailed explanation, Moodz. Is that the answer you give when you haven't got an answer??

I was not answering the question ... I was stating that "you" are incorrect. This is the standard answer for people who ask incessant questions whilst never contributing to the conversation.

[UrbanFox]

I was not answering the question ... I was stating that "you" are incorrect. This is the standard answer for people who ask incessant questions whilst never contributing to the conversation.

You would like me to contribute to the conversation....OK, could I ask you to throw a couple of handfuls of dirt in front of your test coil and then wave your targets around again and post a couple of the resulting waveforms from your oscilloscope...if you understand what I am getting at? Give me something constructive to converse about!