Graphite or not graphite around the coils?

[Freddy67]

Hello to all

A question that may seem elementary.
Should - be put graphite or aluminum foil around the coils and why or why not?
I think it is not necessary that the loop is closed if you put a shield.

Greetings

[jap]

Hi Freddy67
-In PI not necessary to use a shield.
-In VLF must & necessary to use a shield graphite or aluminum or two,the loop shield is not closed ,it 1~2cm gap.
best time
j.

[Davor]

My coil is gone FKK, but it is centre tapped.

[Freddy67]

Thanks Jap for the quick response.
Is it necessary to shield the two coils or only RX?

Best time

[jap]

Hi Freddy67
I saw a little VLF DD COIL work and only one D is a shield,,its work!!!!,This suggestion from the person who has worked this - I did not try it.
best time
j.

[jap]

My coil is gone FKK, but it is centre tapped.

Hi Davor
Are you changed in the pcb components of RX,TX insert.? Or placed inside in coil.
best time
j.

[Freddy67]

Logic would dictate that it is the Rx that is shielded coil Tx receiving no parasites.

Regards

[jap]

Hi Freddy67
Yes it is the Rx that is shielded coil - but I could not identify because it Video.
best time
j.

[Freddy67]

Thank you for the pdf file. Very informative.
Hoping this post serves to others.

Best time

[satdaveuk]

Depends what format detector your talking about and where and which country your going to use it, Induction balance at the very minium needs RX coil shielding but over here both RX and TX is required, , Pulse induction over here needs shielding , its all about mineral and iron content me old mate.

Regards

Dave

[Davor]

Hi Davor
Are you changed in the pcb components of RX,TX insert.? Or placed inside in coil.
best time
j.

My both Tx and Rx coils are FKK. No graphite, no zinc paste, and God forbid no foil. But my Rx coil is with a centre tap going directly to a signal ground, so it takes care of a common mode just as shield would, but without masking problems of a foil. It works because IGSL has a differential frontend option, otherwise it would not work without some kind of transformer, inductive or electronic.
When I think about it, I wish I wound a Tx coil with a centre tap as well, because I could have some 12dB more on a Tx side. Too late now. Will be more clever next time though.

In case you are bound to some commercial rig, most probably you are not able to employ a naked coil because your rig's frontend is not ready for such coil acrobatics.

...its all about mineral and iron content me old mate.

I wouldn't say so. I searched salt soaked beaches brim full of iron and foil junk (exposed directly to Bora), and did not experience anything beyond expectations from a good detector with a good coil. Centre tap works.

[Freddy67]

Thank you Satdaveuk.
In the case where the two coils are shielded, is that the shields of two coils can touch or should isolate where they touch? I do not know if this is understandable, it is the Google translation

[Davor]

They will "touch" this way or another when you connect them to a signal ground, which is common for both coils. In theory you can touch two foil shields in a single point, but not two points because you'll be forming a shorted loop, and that's bad. When low conductance materials are used you can spray them everywhere - such loops will be far from shorted.

[Freddy67]

Thanks to you Davor

>> They will "touch" this way or another When You connect a signal ground, Which is common for Both coils. <<
That is logical. Am I stupid!

[satdaveuk]

Hi Davor
Your concept is new to me the only centre tap ive had experience with is transformers which had nothing to do with metal detectors.
Your design oviously works in your country wether it would be a sucess over here remains to be seen. When time permits may build the IGSL,with your mods and coil advise, got a board and all the parts just never had the urge to build it, made two Ivonics TGSLS there ok and 10-15 years ago they would have been classed as brilliant but now there nothing to right home about compared to some of my comercial detectors that I own.
Far as the shielding the chap asked about on here, I was commenting on experience of the coils and projects over the years that ive personaly built and field tested here in the uk, not any other country because ive never detected overseas if I did then it would be meaningless and misguiding to him, but of course if he has your centre tap format which I very much doubt then your the man to talk to .

Regards
Dave