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Time Domain Signal analysis
- Thread starter dirtdog
- Start date
I think design engineers recognize two types of detector for our hobby. Pulse induction (Time Domain) and continuous wave or sine wave (Frequency Domain) If the coil is drive by a square wave then upstream it can be TD or FD. As an example the Explorer is Pulse Induction and uses TD art upstream. The DFX is Pulse Induction but uses FD art upstream. There is a major difference up stream and they do use both. Glenn, has pointed out several times that TD is looking at the temporal evolution of signals while FD is looking at phase angles.
Not abstract this further,but why can't you use some sort of quantum modeling to proses the incoming signal? My self personally. I think microwave Down and up with high level digitalization would be the ticket if it was not so power hungry! Really there in lies the problem one can design something to blast ten feet down But you need an extension cord to power it
Detectors are in a class of electronic equipment that is not limited, I think, in power since the electromagnetic field does not actually get transmitted. The fields are like the ones around the electrical wires in our homes. So, why not just really blow the signal down? Here are a couple of reason from what I have read. The field can be driven so hard that it will cause magnetic soil to retain the magnetism and that would be a major problem. Also, test have shown that the drive that is currently being used is all that is needed. There would be some real power supply problems in supplying the needed power. Depth is not the major issue, although that seems to be with users, it is discrimination and separating the tiny signals from good targets from noise and trash.
A
Anonymous
Guest
n/t
Check out the PI technology forum. I posted there specifically on the question of whether the ML/ whites/ Fisher multifrequecy detectors are pulse or not and the difference between time & frequency domain. People that actually build and sell PI detectors gave the straight poop on the whole subject. The conclusion is.. PURE BS! ...Willy.
I think what is happening is as follows (and I hope my explanation is not too confusing):
Lets say that two frequencies are to be analized by the receiver and are arranged such that the lower frequency is the same as the pulse repetition rate of the transmit pulse and the higher frequency is a harmonic.
If the higher frequency is not a small multiple of the fundamental pulse repetition rate, the energy content being radiated at this higher frequency is just too small (a consequence of the Fourier series expansion of a contant repetition rate pulse train) to be of practical use in detecting a signal back from the target. In other words, there is just to little oomph being transmitted at that frequency (compared to the fundamental) to obtain a response back from the target with a good signal to noise ratio.
To get around this problem, the DFX (and I think the Ex does the same), the transmitter is designed so that instead of generating a constant repetition rate pulse stream, it varies the repetition rate periodically. This has a profound effect in the Fourier spectrum being generated. By choosing the change in repetition rate correctly, one can dramatically increase the energy content of the desired higher frequency. The problem is that this "energy peaking" is not constant, but it occurs at specific repeating times, which is of course related to when the transmitter changes repetition rate.
Thus, in order to anlyze the signal at this higher frequency, one needs to look at it at the correct time. We need to take a sample of this higher frequency signal coming back from the target, in a manner that is time correlated to when the trasmitter circuit is generating the maximum amount of energy at this higher frequency . Note that the analysis is still one that we think of as frequency domain (that is we want to generate the ratio of the X and R components of the signal), except it has to be done at the right time relative to the transmitter.
I think this is what causes the confusion about time domain versus frequency domain. Hope the above was understandable.
Lets say that two frequencies are to be analized by the receiver and are arranged such that the lower frequency is the same as the pulse repetition rate of the transmit pulse and the higher frequency is a harmonic.
If the higher frequency is not a small multiple of the fundamental pulse repetition rate, the energy content being radiated at this higher frequency is just too small (a consequence of the Fourier series expansion of a contant repetition rate pulse train) to be of practical use in detecting a signal back from the target. In other words, there is just to little oomph being transmitted at that frequency (compared to the fundamental) to obtain a response back from the target with a good signal to noise ratio.
To get around this problem, the DFX (and I think the Ex does the same), the transmitter is designed so that instead of generating a constant repetition rate pulse stream, it varies the repetition rate periodically. This has a profound effect in the Fourier spectrum being generated. By choosing the change in repetition rate correctly, one can dramatically increase the energy content of the desired higher frequency. The problem is that this "energy peaking" is not constant, but it occurs at specific repeating times, which is of course related to when the transmitter changes repetition rate.
Thus, in order to anlyze the signal at this higher frequency, one needs to look at it at the correct time. We need to take a sample of this higher frequency signal coming back from the target, in a manner that is time correlated to when the trasmitter circuit is generating the maximum amount of energy at this higher frequency . Note that the analysis is still one that we think of as frequency domain (that is we want to generate the ratio of the X and R components of the signal), except it has to be done at the right time relative to the transmitter.
I think this is what causes the confusion about time domain versus frequency domain. Hope the above was understandable.