directed coil for pi detector

[Orbit]

- directed coil for pi detector ,Is it something like that patented ?
which detects Metals on one side only coil hmm !

[chemelec]

Why? Do you have one?

[Silver Dollar]

You have to do a patent search, it could take a while. There is a collection of patents here on
Geotech that you could start with.

Look here under coils; http://www.geotech1.com/cgi-bin/page...le=patents.dat

I thought the shield with a gap in it makes a direction finding antenna of sorts....

[chemelec]

The Gap in a Shield is Required.
Without the Gap, the Shield will Stop the Coil's ability to detect metal.
It has nothing to do with Directionality

[Davor]

...I thought the shield with a gap in it makes a direction finding antenna of sorts....

It does, or better say - it did. Nowadays the shield is replaced with a balanced preamp which works the same, and makes for much lighter and easier to produce antennas.

[Orbit]

- that I did prototype working !
has nothing to do with the shield It is shape of coil ,I'll show you soon on video clip will see that this is possible !means that detected metal just below coils the target while on the upper side, there is no detection ....

[Tinkerer]

It does, or better say - it did. Nowadays the shield is replaced with a balanced preamp which works the same, and makes for much lighter and easier to produce antennas.

Problem with balanced pre-amp

The balanced coil, twisted pair cable and pre-amp worked just fine.

Then something happened.

What happened might just give us some clues of how the shielding works.

The TX and BU used and the bi-filar wound center tapped RX coil worked just fine. Very good sensitivity to very small targets and no response to the hand on the coil.

Then, suddenly I got extreme sensitivity to my hand and even my body within 1 meter from the coil. Moving my hand 50 cm above the coil I could play the VCO like a musical instrument by just moving the hand in the air.

Since the RX circuit is on a breadboard, I suspected a bad connection that caused a ground loop.

When I went to wiggle some contacts, I got a spark from my fingers to the board. The size of the spark indicated static electricity of several thousand volt. Surprisingly the circuit still worked afterwards, but it is obvious that I need to do something about it.

This is my first experience with static electricity, only knew it from the books, because I always lived in places where the humidity in the air did not let static accumulate.

So? what does this tell us?

What is the best way to make a ground to discharge the static to?

[Davor]

Keep a watch on a common ground. Even a shield does that. Centre tap connected to a common ground should fix everything else.

[Tinkerer]

That is fine for the circuit, but what about myself? When I get statically charged, anything I touch may get zapped. Maybe a earth cable to the water pipe? Or is the mains earth terminal better to connect to?

[Davor]

If you speak of your shack, and you have problems with static, it is a good practice to get a wrist band with 1Mohm in series to connect yourself to some kind of ground. I don't know about your place but here every electric installation must have a proper grounding to the earth, so using a ground wire is OK - provided the installation is 10 years or newer. You can also spray some water as a quick fix, and if you need something more permanent, use air ionisator. You can also light a candle (no kidding) to increase air conductivity - it helps as well.