Question for anyone that knows their coils "inside & out" :smile:

[D&P-OR]

This is one that I (and I'm sure others) have been curious about so bear with me a bit while I ask it.-----The coils (11" DD, 5" DD & 10" concentric) for the F-75/70 and the Omega are the same physical size (coil mold).--The coil cable connector (to the control box) is the same (will "hook up" to either detector).---We all know that the F-75/70 operates at 13 khz & the Omega at 7.8 khz.------HOWEVER, the coils on the 75/70 CANNOT be inter-changed with the Omega (at least for optimum performance).-----WHY IS THIS??----Is it because of the diameter of the inner coil windings--the positioning of the inner coil windings--the size (diameter) of the wires in the coil cable itself (to the control box) or a COMBINATION of these things? (to make these coils compatible or non-compatible with these detectors)------Haveing said all this--the bottom line & to simplify the question.----What makes these same (physical) same (connector) coils different??-----Can someone explain this to some of us "electronic challenged" folks out here?-----NO GUESSES PLEASE!! ------------Del

 

[zeekeys]

Del it is the length of the wire, how long the wire is. ....Z

 

[D&P-OR]

Thanks Z-----So it's the length of the coil inner winding (wire) that determines the Khz of that individual coil (that it will produce).---I think I said that right?-----Is the diameter of the coil inner winding (wire) a factor?-----Who says you can't teach an ole dog new tricks--I'm learnin something!! ----------Del

 

[zeekeys]

Del I do wish someone who really had the detailed answer for you. Here is my take on it. Basically we have an antenna (coil). It transmits and it receives on a certain frequency.
I use to make my own antennas when I was a kid. Get a length of wire put it on the ground and measure it off and cut it and make the antenna. One was 137' another 76" and so on. I did that with a yard stick on my knees measuring.
I notice that almost every manufacturer makes same size coils. So there must be a standard size to receive the signal some where in the middle of the field on the coil. I think that for every frequency there is so many turns on the coil. This comes form, I wound coils for transformers. I wound different sized wires at different lengths on different coils depending on the juuce that was going to go through the coil to produce the desired result.
Of course all of this comes from my memory of 50 years ago. So it could be a little distorted.
Del I could be way off base. It wouldn't be the first time. But you have a very good question and it should be answered.
This is just my 2 zinc pennies worth. Not worth much if you think about it....
Thanks for reading ... Happy Trails....Z

 

[D&P-OR]

Thanks again zeekeys.----I really appreciate you takeing the time to explain that to me, I understand it a lot better now.---It's nice that you got a memory to draw back 50 years on.---I try to draw back 50 years on my memory & I STILL come up with a "blank" (I'm 71 now)------Seriously though, it's nice to know a little more about the "make-up" of before mentioned coils.-----Take care my friend, Del

 

[zeekeys]

Well Del the memory for me gets twisted. I some times put 2 or more incidents together to come out with one story and I really don't realize it until much later that I had done that.
I will be 69 next month. Love metal detecting. My wife loves it too because I am gone for a few hours.
Some times I only detect and hour in a 3 hour hunt because people come and ask me about md'ing. So I have been known to carry on a little. But it is all right because it is my time and I am doing what I want to do... Thanks for reading and Happy Trails....Z

 

[Goldbug Ron]

Del,
A brief technical explanation of a coil. The coil is wound using a mathematical electronic formula. It is wound to a certain impedance. Impedance is a mathematical combination of resistance, inductance, and capacitance. The length of wire, type of wire, diameter of wire, number of turns, spacing between turns, all combine to produce a specific impedance. The output circuitry of the detector is designed for a certain impedance. These impedances must match to work correctly.

Different coils have different impedances. Even though the coils look the same, and have the same connectors, they would not work correctly if the impedance doesn't match.

Technical, yes, but I hope that helps a bit.
Goldbug Ron

 

[Alimo88]

R = resistance in ohms
C = capacitance in Farads
L = something in Henery's. this is to do with the coil winding. this is the length and diameter of wire and diameter of actual coil
Z = impedance in ohms as well I think. But impedance is AC and resistance is DC
F = frequency in Hertz ie 10 kHz
Its a very complex relationship between all of these when it comes to detectors. And who knows if a coil has a capacitor or extra resistor somewhere in the circuit??????

If we knew the design factors we would all be able to make out own "perfect size coils"

 

[D&P-OR]

Thanks guys----There sure is much (complexity) in the make up of different coils isn't there!!---I don't claim to understand all that has been said here (not smart enough) --but at least I know more about coils now than when I asked the question.----I'm sure there has been others that have read this post with interest also.----Thanks again, much appreciated.---------Del

 

[gazn357]

Without dusting off engineering books...

You have better power transfer with impedance (Z) matching. Capacitance(C) and Inductance(L) both have frequency components. Length of coil wire is probably calculated to match frequency wave length (1/4 wave, 1/2 wave, full wave ). Would expect most coils are designed/tuned for particular frequency. When impedance is properly tuned for a particular load, you will have a pure resistive load ( Reactive components of C and L cancel out).

Google impedance matching.

Danny