Some advice on coil selection/design, creating, and measuring needed!

[Tinkerer]

So using this calculator, what are the parameters you inputting and what type of coil are you using if you say intend to make an 8" mono.
It was choking on my inputs. Also it keeps saying the program is too old and to contact the author for a new version.

The program ask from time to time for an update. (free)
Below is the screen for an 8" coil, 300uH
The second picture is of the coil current at 101us TX

[bklein]

How do you enter a wire diameter less than 1mm? That's what was stopping me. It wouldn't take ".511" for 24AWG for example.
Also I note that it says the coil resistance is 370 mohms and in the upper section you used 1 ohm. Will it take less than 1 ohm?

[mikejr0046]

heavy wire

How do you enter a wire diameter less than 1mm? That's what was stopping me. It wouldn't take ".511" for 24AWG for example.
Also I note that it says the coil resistance is 370 mohms and in the upper section you used 1 ohm. Will it take less than 1 ohm?

.511 is just over 1/2 inch,maybe you want .051

[bklein]

The default measurement is in mm. - but looks like 1mm is smallest you can enter(?)

[Tinkerer]

The default measurement is in mm. - but looks like 1mm is smallest you can enter(?)

Try 0.511 for the wire thickness/

The resistance shown is 370mili Ohm. for 0,511mm wire the resistance will be 1.4 Ohm.

For the coil current I used 1 Ohm total resistance, like Mosfet 450mOhm, wire 370mOhm, cable etc. 180mOhm= 1 Ohm total resistance.

When you use plastic insulated wire, rated 600 V the bundle thickness will increase. Note that the inductance decreases as the bundle diameter increases with the same wire.

When you wind a bundle coil, the inductance changes also depending how tight you tie the bundle.

[Pete the Builder]

MiscEl is a windows-only application. I've asked about the possibility of a Mac port, but I doubt that will happen.

FWIW, MiscEl seems to run OK under Parallels 7 windows emulator.

Now to start learning!
-PtB

[Pete the Builder]

Thank you all for the great explanations of the differences to expect. This is all being taken on board, I assure you...

I have so many more questions, but I've worked through Carl's wonderful articles, and I'm sifting the silt from the nuggets in the patents.

Interestingly, many of the "top of the head" ideas I had early on were patented by someone years ago! So that's nice to know - I'm thinking more or less the right way. It's the application of the knowledge that's important...

So. Next ridiculous question. Why not use a long, vertical, ferrite-cored inductor to induce the EMF into the ground, instead of the big, wide air-cored inductors we're currently using? We could still use an air-cored RX coil(s), to ensure we have a wide pickup area beneath the coil. A vertical cored inductor would induce an intense and penetrating vertical field, with a far less intense horizontal component, wouldn't it?

My next thought would be to use a U-shaped core, like a C or E transformer core, to do the same thing - the field wouldn't be "wasted" in the air, it would primarily be focused into the earth. Bung a lot of current through an appropriate winding every 100mS or so, and I'd imagine the induced eddy currents would be an order of magnitude larger, all else being equal. Obviously, there's this big lump of ferrite or iron that you have to manage physically, which would be a problem, but not insurmountable, with the appropriate counter-weights and fulcrum points.

Using a metal core like that would also mean less TX field would be induced in the RX coil, wouldn't it? It's a win-win! Which means, since no-one is using it, there must be a huge problem I'm not understanding... What am I missing?

Thanks for all explanations. I realise my poor grasp of winding fundamentals is an issue - such as why a shorted turn is so bad, why an open loop can't work, etc... Sigh.
-PtB

[ODM]

Ferrite cores are in use with some pinpointers and handheld frisking detectors, for pinpointing nearby objects.

I believe the answer for why smaller cores aren't in use is in the sparsity of the field. If you draw a 45deg cone from a coil of a particular size, you can estimate where most of the induced field from a target falling inside and outside of that cone would be going. This would also relate detection depth vs. coil size which is apparent.

The same goes for ferrites - the friskers usually use long rod cores, and are more sensitive to distant targets from their side compared to their tip, when the target is parallel with the rod core. Try it out with a rod antenna connected to a scope, and another loop to inject a signal from different directions and orientations.

[Davor]

Ferrite saturates. And iron is noisy (Barkhausen effect).

[Tinkerer]

CALCULATING COILS

http://hyperphysics.phy-astr.gsu.edu...ic/curloo.html

Mathematics make a knot in my stomach. Fortunately with the Internet, one can find a calculator for everything. I use the above one to calculate the field strength.

Play with the diameter and look how the field strength diminishes at the distance.