Find Large Inductance Without Meter

Assumption, the mother of all screwups.

You're assuming that the "20,000KHz" is 20K ohms. I'm not. If you leave the "K" in place, it could also be 20 MegOhms. Toss a coin?

The OP hasn't bothered to supply any clarifications or reply to any specific questions, so we don't know the real resistance. It could be anything. 20K ohms is unlikely. Cut-n-pasted from my rant upthread: If 20K ohms, your coil must have an enormous number of turns, look more like an open circuit, or you blew the measurement. If it was really fine gauge wire such as #40AWG, with a resistance of about 1 ohm per foot, the winding would be 20,000 ft long. Post a photo. I want to see this thing.

In OP's absence, I'll speculate that he's building an induction coil magnetometer. Table 1 on Pg 53 shows some typical coil parameters. Resistance = 48 ohms Inductance = 0.306H Relative permeability = 3500 (probably ferrite, not mu-metal which is about 10,000) Number of turns = 2350 Operating frequency = about 1KHz (my guess from the graphs) That makes such a coil less exotic and rather mundane.

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Jeff Liebermann     jeffl@cruzio.com 
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Correct. But that does not mean that it is useless. Just because it does not resonate at 10Hz, does not mean it will not sense 10Hz. Turn in your degree now.

What is your "assumption"? How about 20k turns of wire? Didn't consider that, did you?

Speculation, the father of all screwups. "Guess" is the offspring of the mother and father.

It's obvious that you can't read. He want's to *resonate* it at 10Hz, dope!

If you want to pick up fluctuations in the earth's field, there are some interesting points.

20K of copper resistance will have around 18 nanovolts/rootHz of Johnson noise. That will dominate signal-to-noise ratio. A decent opamp will contribute essentially no added noise.

At a given radius, more turns increase signal linearly but adds Johnson voltage per the square root of turns. So s/n goes as the square root of the number of turns. Square root is a discouraging function.

A bigger diameter coil adds signal per radius squared, and adds Johnson noise as the square root of radius. That's a pretty good deal... use a big coil made of heavy gage wire. A shielded multiconductor cable might be good, a big loop with the wires wired in series. Total resistance ballpark 100 ohms might work.

Given a big coil, there's no reason to use a ferrous core.

A flux gate would probably be better than an inductive pickup.

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John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

It's obvious that you can't read. How stupid can you be? What's wrong with you? If it won't resonate, it won't resonate. Damn, you're more stupid than stupid! I'll bet your family moved away while you were out and left no forwarding address.

Not as stupid as you, apparently. I said exactly the same thing to you just a few posts up. You really are an Slowman-class idiot.

you just a few posts up. You really are an Slowman-class idiot. "

Hold on here K, we can't really pick on Slowman's technical abilities. He d oesn't post about that, preferring to tell us how to run other countries an d how advanced the outback is. Like how we need to get rid of out guns and sing Kumbaya with the thugs who stole our tires (tyres) last week. (because they were disadvantaged of course)

I am glad the US election is over, now in a month or two we can get back to talking technical shit. Unlike "certain" others I admit I do not know ever ything and I learn something here from time to time.

As an engineer, he's unemployable. He's been "designing" a stupid oscillator for a couple of decades. Technical abilities?

Dream on.