Basic concentric design

[dfbowers]

Is there any kind of screen inside the top shell?

[kt315]

The screen at the top helps against electrical interference (high-voltage wires, cell phones, etc.).

no no no. the screen at the top and at bottom too helps from electrostatic fields in wet conditions - to be a wet grass in rainy day, morning dew etc. NOT FROM THE HIGH VOLTAGE LINES, CELL PHONES, RADIO WAVE SOURCES, ETC.

[dfbowers]

I question the necessity of a "screen" at all. The first concentric I built (this one was for the IDX) I hunted all afternoon in the rain with no problems at all..completely stable with just a graphite covered paper shield. The next 3 coils I sprayed the inside of the shells with graphite. I have not noticed any issues with them either.

[kt315]

- a graphite covered paper shield is some kinda 'oldie design'
- 'new modern one' is sprayed inside of the shells by graphite aerosole.
- 'modern progressive' are some Garrett coils, conductive based graphited reels for the coils. conductived itself. this way means the shells are not covered by graphite.

[Davor]

My coils are avant-garde then No shield at all

OK, I use centre tap.

[golfnut]

I guess if you had a top and bottom LIDS - then sure add paint to both halves -why woudlnt you. I get this.


What I dont get is,,

Specifically on a concentric spider, (like tesoro, 9x8 or a whites 9" circular) the shell has carbon paint in it - (ive seen it on tesoro shop video) the coils go in, the operator adjusts it all, then, this is the point it all goes a bit dark.


Does the potting resin have lots of carbon in it to form the other half of the E-screen. ( As this is the side that looks at the ground )

Do you put a graphited paper ring in on top of the coil - touching a ground pad - then Pot with normal potting compound.??


(You could do ally foil or survival blaket and wire but bit of a chore)

Do you not bother with closing the box ? Is the E-screen only on 3 sides??

Last question here honest guv

S

[kt315]

My coils are avant-garde then No shield at all

OK, I use centre tap.

your coils are NOT avantgarde. you are living in dry hot climate and maybe do not need in the shield like me or someone yet living in rainy county.

[dfbowers]

I guess if you had a top and bottom LIDS - then sure add paint to both halves -why woudlnt you. I get this.


What I dont get is,,

Specifically on a concentric spider, (like tesoro, 9x8 or a whites 9" circular) the shell has carbon paint in it - (ive seen it on tesoro shop video) the coils go in, the operator adjusts it all, then, this is the point it all goes a bit dark.


Does the potting resin have lots of carbon in it to form the other half of the E-screen. ( As this is the side that looks at the ground )

Do you put a graphited paper ring in on top of the coil - touching a ground pad - then Pot with normal potting compound.??


(You could do ally foil or survival blaket and wire but bit of a chore)

Do you not bother with closing the box ? Is the E-screen only on 3 sides??

Last question here honest guv

S

Just a suggestion.. Graphite spray is easy. The only issue I could see with this approach is getting the epoxy to stick.
The graphite spray I have been using almost melts itself into the plastic anyway from the liquid carrier in the aerosol.

Don.

[Davor]

your coils are NOT avantgarde. you are living in dry hot climate and maybe do not need in the shield like me or someone yet living in rainy county.

No, looking into ITU's rain maps my country is even rainier than UK, and terrains on Adriatic coast are dominantly terra rossa, so it is surely more difficult than you think.
The whole point is that a centre tap is doing the common mode grounding quite effectively. Truth is that a differential mode preamp is ~3dB noisier than a single ended preamp, but even that can be fixed by using - a better differential preamp.
Practically all of the popular projects are using suboptimal preamps with regard to noise, so the 3dB difference between single ended and a balanced input is purely academic.
Electrostatic pickup comes as a common mode signal and it would normally be suppressed by a good balanced preamp. A centre tap provides additional attenuation of several decades and IMHO this approach is far superior to shielding in amateur builds as it leads to a clean solution without much unnecessary steps. It works for me just fine even with suboptimal preamp.
In a single ended solution you rely to a shield to ground the electrostatic pickup. It is fine, but tedious, and in case of graphite messy.

[kt315]