Theories about coil-shielding

[golfnut]

Yes it is insulator, not carbon black. I have graphite, but wanted carbon black and graphite mix trial.

Toner will be going back on the bay.



I would like to know what the mechanism is for the falsing, with inadequate screen.

It may be that leaked E Field from Tx coil is coupled to the Rx coil using the dielectric properties of the soil

it may be

Tx signal phase shifts with proximity to gnd
OR
Rx signal initial phase may skew in sympathy with proximity

[golfnut]

If one had a metallic sheild and new what the air distances were. The user could add a resistor across the end / gap -- when the R value got too low the distance to detect would suffer.

This isnt quite the same as discussed but may give first order pointers. S

[Kev]

Howdy,
On my PIs I've had very good results with the conductive paint from Stewmac, I think it's actually Aquadag, it's almost identical to what Nugget Finder and Coiltek use. I actually water it down a bit, it goes a very long way, and easily produces the 70 to 50 Ohm per inch my Minelab requires.

On my VLF coils I'm getting good results using mylar from inside large capacitors. I'm not sure if they are Polycarbonate, or Polyester. I'm using some from work that were being tossed out. They are X2 caps, so they are designed for mains voltage which is 230V where I reside, and thus have high insulation resistance. Which seems to mean that the mylar is a reasonable thickness, in fact it is almost see through, but much thicker compared to low voltage types.
In these caps the layers are twinned up so I first separate them and then wind one layer on the coil conductive side up, and then do a second layer conductive side down which overlaps the join of the lower one. This gives around 50 Ohms per inch, which is way below George Payne's recommendations, but since the current has to wend its way around a maze of curls and turns it seems to not generate much of any extra noise in the machine.



Worth an experiment anyway, it may just give you a real hot loop. One things for sure, it makes for a very fine screen, much better than cooking foil, which I believe along with others here, causes way too much signal attenuation.

It will work on PIs as well but it requires a bit more work for the GPXs.

Old computer PSUs maybe a good source.

Cheers
Kev.

[Henrikras]

Graphite test

Made a small test... See pictures.
I a CD plastic cover, clean first with acetone, then one lay with the mixture. And wait 5 hours to it dryed up.
I made 3 drainwires at the left and the right at each CD cover.. (Same type I'm using in the coil work)
This alcohol I got is buyed in a drugstore, ist used to clean Medical tools, but I Allways used it to clean good old VHS videos videohead. It seem to make the mixture nice and smooth.
They could Be some other types of alcohol getting the same good results. !!
Its a good idea to use a brush with many hairs... To stiff brush will not Be good.
Henrik.

[golfnut]

Really good science there Henrick.


I made some using low viscosity epoxy and did 40% graphite 60% epoxy by mass and got 8kohms/sq - not great.


I think the particle dont touch each other very well - like a pile of bricks..


My theory is a smaller particle - filler is required to bridge the graphite 'Chunks'


If I get say 30um carbon black I will try with my 120um graphite and binder like thinned cellulose car paint, or maybe acetone. Steve

[golfnut]

This looks promising but hard to obtain

http://www.lion.co.jp/en/chem/produc...n/carbon01.htm

[Henrikras]

Maybee you can ask them one small test packets ... 4 kg If it wouldn't work in coil work.
Did you find out the cost of this ?

[golfnut]

No I just surfed and found the site and the product.

I will ask them for a sample - Or we both could and compare results?

Steve

[Henrikras]

I'm in If you can get something Gulfnut - Of course some cost is okay.
Just made the shielding at a 15" coil inside with my own mixture - graphite powder and propanol alcohol. - Looks nice.
Not proper dryed up yet to measure. Looks like low resistance, I like that.
Henrik.

[golfnut]

Yes looks good.

I asked them about price and delivery and if I can get a sample.. It is Japan, so may be slow..

[Henrikras]

Okay Steve.. We can hope that they are what Japan i know for.. Nice People and Very helpful.

[golfnut]

This is reply

Thank you for contacting us and asking sample of Ketjenblack.
Unfortunately, we can not sell Ketjenblack in UK because Akzo Nobel has a right to use trademark "Ketjenblack"　in UK.
If you need "Ketjenblack" , I have to ask you to get in touch with Akzo Nobel.
But we can sell powder type of "Ketjenblack" , it's brand name is "Carbon".
Please reffer to the information of "Carbon" as bellow.

Product name : Carbon EC-P → Powder type of Ketjenblack EC-300 (FOB Tokyo USD35/kg)
Carbon ECP-600JD → Powder type of Ketjenblack EC-600JD(FOB Tokyo USD60/kg)

And we have just developed new grade of conductive carbonblack named "Lionite EC-200L" .
"Lionite CB" is developed for customers who faces the difficulty of dispersing.
If you need the carbon which is easily despersed, we recommend you "Lionite EC-200L".
"Lionite EC-200L" is produced in same production line as "Ketjenblack" and with same ingredients.
The price of "Lionite EC-200L" is USD23/kg in FOB term.

If you need more infmormation , please feel free to ask me anytime.

[Henrikras]

what to do Steve... More powder experiments ???

[kt315]

the frik tells you about electrostatic charge you are protecting your coils from https://www.liveleak.com/view?t=uh6d7_1532111278

[Andi68]

A Clown.....