RX coil and sensibility

[Tony60]

Hi Dbanner,
I have tested graphite paint with not good result. Now I,ve find a TV cable with mylar shield inside; I remove graphite paint and use this shield.
Good by and good week.
Tony60

[dbanner]

I can suggest that you read through the various threads on coil shielding , it will give more insight into various experiences by other members. Some even make there own soup concoction containing graphite powder.
I used the shielding from the cable company wire coming from the road to my house, and it worked for me, so I looked no further!!
I'll post a photo of the cable stripped to reveal the shield.

[dbanner]

I noticed that there is a green coating on the inside of the outer tubing. I wonder now if this is the actual mylar coating and the other is aluminum. Yikes!
Anyway, the big boys use graphite for shielding coil housing, so in the end, this is the best way for shield. Remember, it is for shielding the coil from the ELECTROSTATIC EFFECTS of proximity of coils to the ground.

[waltr]

Hi Dbanner,
I have tested graphite paint with not good result. Now I,ve find a TV cable with mylar shield inside; I remove graphite paint and use this shield.
Good by and good week.
Tony60

Can you please describe what you mean by "not good results"?????

Remember, it is for shielding the coil from the ELECTROSTATIC EFFECTS of proximity of coils to the ground.

Exactly.

Ideally the coil/detector will have the same target response with or without a shield.
Also, the shield will NOT Stop EMI (like electrical noise inside your house).

What it should do is prevent false beeps when moving the coil across grass and the ground or when touching the coil housing.

[Tony60]

Hi Waltr and Dbanner,
then with graphite, after having balanced the coil, the sensitivity decreased and the MD made sounds, and I had difficulty balancing the ground with ferrite. The TV cable I found in the warehouse is like the one in the posted thread. I haven't had time to try the new screen yet but I'm confident.
All the best and bye bye.
Tony.

[didier]

Hello Tony,
can you please give your feedback with the coax foil you were trying for the shielding as a subtitute for the graphite shield? is the Al shield it better than the graphite shield?

how did you assemble the graphite shield to the coil? could you please describe it step by step?

did you apply a tape first around the copper windings of the coil, then You sprayed the Shield? is the Graphite 33 like a paint and is it mechanically stable? did You also use a thin wire over the graphite Shield to lower the resistance? and did You leave a gap in the Shield for Rx and Tx coil?

I am very interested to have some more Information about the Graphite Shield because I also want to use it for my next coil but when I read through the forum it is very confusing. there is no clear answer if a aluminium shield or a Graphite shield is better. some claim that a graphite shield gives a better sensititity. so I am astonished that you were not satisfied...

[waltr]

Not tony but have built TGSL and DD coils.

I first ensure the coil bundles are secure. I used Dbowers method (see his TGSL 101) using polyurethane.
Next is wrap with electrical tape.
Then a very thin wire (BARE #32) wrapped with wide spacing (about 1.5cm) on the coil. Leave a length to solder to cable shield/ground but leave gap (no shorted turn). This is the "drain wire"
Next is a coating of Graphite. 33 I hear works well. I make a paint with fine graphite powder and polyurethane.
Allow to dry and test with Ohmmeter from drain wire to spots with graphite. If resistance is too high put on another coat of graphite and repeat drying and measuring.
.
Once this is good then cover coil with another wrap of electrical tape.
Fit coils into shell connect leads to TGSL TX-RX and adjust for Null and correct TX to RX Phase.

The shields of the two DD coils should Not touch. the last layer of tape ensures this.

As to Aluminum verse Graphite shield---there is no clear answer.