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My Home Built PI Detector

Hi Smitty,
You are correct in that your shield is a Faraday shield and also prevents ground capacitance effects. You will find that it does reduce EMI but only for frequencies higher than about 5MHz. With the coil vertical, where you get maximum rf pickup, disconnecting or removing the screen will have a noticeable effect if you look at the high frequency noise on a scope and a wide band preamp. A detector coil works on the magnetic component of an rf field rather than the electric component as a normal wire or rod antenna does. In fact I use a 14in Coiltek mono coil as an aerial for my workshop medium and long wave AM radio as it cuts out a huge amount of interference. The best type of coil for reducing interference within the pass band of the detector is a figure of 8 winding.

Eric.
 
Eric

Thanks for your input on the coil shielding. I am in 100% agreement. The swamping out of the ground capacity and the effects of vegetation is the primary effect of the shield. Without the shield the coil is almost impossible to use.

My PI does really well on small gold targets since I designed a dual gain receiver amp to reduce the gain as the amp approaches saturation. Preventing saturation eliminates the saturation delay and allows me to sample in the. 5 to 6us range to improve tiny gold target detection.

Thanks again Eric!

Smitty II
 
Hello Smitty II,

I am new to Find's forums, and have a little background in digital electronics.
You seem to have quite a bit of E engineering experience.
I am trying to learn more about Op amp circuits and play with oooold detectors of the transmit/receive low frequency types.
I have purchased a few 'Vintage' era detectors to take apart and examine - draw up the schematics and try to understand.
Would like to work on some 'surface mounted component units', but find multilayered boards hard to trace.
It appears that much of the Tech Forum section here is heavily involved in PI type units.
Does anyone still dabble with transmit/receive units?
I have millions of questions.
Is your 'Home Built PI Detector' your own design?
Thanks.
Mike D.
 
Your detector looks great!
May I ask how or where did you acquire the circuit board - fabrication?
I am looking on the internet for detector kits and have found thousands of videos on various stages of construction, but no mention of where to purchase them.
Any ideas?
Thanks.
 
Greetings

I laid out the PC board and had some made. I have some extras!

Smitty II
 
Mike

Yes! It is basically my design, but like most of the home built detectors out there, it has distant roots in other designs. About 50% of the circuit will not be found in any other detector.

My circuit boards are single layer through hole boards. I do not have any SMT boards.

Smitty II
 
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