My Results

[nncunew]

I am making a PI detector, but i am not obtein goods results, one problem is the output of LM709 i see that the signal is very much fast crecient and in the top make a small oscilation.

I am using a 8.2-10 inch coil 20awg 28 turns , a IRF 640 and 100 ohms damper resistor. In the input of LM 709 i am using 1k resistor and 1M for gain.

I think that the small oscilation is not correct, somebody can say me what i can do to eliminate this problem.

Here i make a picture with the aproximate wave form in scope

[bbsailor]

What is the inductance of your search coil?
What PI design are you making?

Off the top of my head, it looks like your damping resistor is a little low. The resistor value of the Hammerhead PI is about 680 ohms and uses a coil very close to your coil. The damping resistance value has wide variance depending on the capacitance stored in the coil, shield, coax cable and MOSFET. Carl notes in his Hammerhead document that it can be between 200 and 800 ohms.

bbsailor

[nncunew]

Ok

I don´t know what´s de inductance of the coils, but I think that a greater damping resitance send very much bad results.

Example, i used a 150 ohms and the oscilation is increasing.

I and making the power pulse same as hammer heat but i using LM 709 like sandbank to front end amplifier.

Thank, i hope the answer

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