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Re: Lets talk coils
Hi Frank,
I am not sure how to answer your question. On a typical PI, the xmit is also the receive coil. If the xmit decay time is too long, then one can not sample as early. So, it is hard to separate the two.
As for pure signal, I am not sure a larger wire would provide a better signal than a smaller wire, but I have not tried any experiments to verify this.
What I do know, is most VLF's use a very small wire for their receive coils. Part of the reason is to reduce the coil weight, but smaller wire is used simply because it will provide the necessary signal.
As for my PI, I find that separating the signal from the noise is the big problem. So I find shielding very important. The biggest problems I see with PI's are, external noise, power supply noise, and internally generated front end noise. This front end noise can be from the IC used, or may partly come via the xmit FET. It is hard to tell or separate the two.
I have tried wire sizes ranging from 30 awg through 26 awg and have not been able to determine any difference in sensitivity strickly due to wire size. Instead, greater strides have been made by selection of the preamp (I am using the NE 5534A), and the use of a DD coil which, among other things, separates the xmit from the receive.
Also, reducing the delay makes a huge difference. This is obvious when looking at the decay signal from different objects. Being able to sample sooner simply provides a stronger signal to begin with.
When reading this, one should realize that I am also focusing on trying to find the best solution for detecting small gold objects also. I really haven't tried to build the deepest seeking detector for iron objects.
Basically, this shortening of the delay and sampling sooner should also provide an overall sensitivity to all targets, providing the pulse on time is adjusted accordingly.
I am not sure I have answered your question, but it is the best answer I can provide at this time.
Reg
Hi Frank,
I am not sure how to answer your question. On a typical PI, the xmit is also the receive coil. If the xmit decay time is too long, then one can not sample as early. So, it is hard to separate the two.
As for pure signal, I am not sure a larger wire would provide a better signal than a smaller wire, but I have not tried any experiments to verify this.
What I do know, is most VLF's use a very small wire for their receive coils. Part of the reason is to reduce the coil weight, but smaller wire is used simply because it will provide the necessary signal.
As for my PI, I find that separating the signal from the noise is the big problem. So I find shielding very important. The biggest problems I see with PI's are, external noise, power supply noise, and internally generated front end noise. This front end noise can be from the IC used, or may partly come via the xmit FET. It is hard to tell or separate the two.
I have tried wire sizes ranging from 30 awg through 26 awg and have not been able to determine any difference in sensitivity strickly due to wire size. Instead, greater strides have been made by selection of the preamp (I am using the NE 5534A), and the use of a DD coil which, among other things, separates the xmit from the receive.
Also, reducing the delay makes a huge difference. This is obvious when looking at the decay signal from different objects. Being able to sample sooner simply provides a stronger signal to begin with.
When reading this, one should realize that I am also focusing on trying to find the best solution for detecting small gold objects also. I really haven't tried to build the deepest seeking detector for iron objects.
Basically, this shortening of the delay and sampling sooner should also provide an overall sensitivity to all targets, providing the pulse on time is adjusted accordingly.
I am not sure I have answered your question, but it is the best answer I can provide at this time.
Reg
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