A
Anonymous
Guest
Can some one tell me what Litz wire is.Thanks
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A
Anonymous
Guest
Radio frequency (RF) signals tend to move through the outside surface of a wire, thus having less surface area and a higher resistance to the RF signal than the total wire diameter would seem to dictate. One way around this is to use multiple insulated strands of thin magnet wire wrapped in a bundle to each carry and share the RF signal. Thus the total resistance for the RF signal is much lower than either a single strand or a single wire equal to the combined diameter of the stranded bundle.
Do a web search on the words "Litz wire" and see the various strand configurations that wire vendors normally stock.
Litz wire is popular among ham radio enthusiasts and those who make crystal radio sets. Their coils are wound with Litz wire to obtain a higher "Q" factor (quality) than would be possible using plain magnet wire with a single core.
One of the Minelab patents on the patents section of the following web site: "http://www.thunting.com/cgi-bin/geotech/pages/common/index.pl?page=metdet&file=patents.dat" references Minelab Coils using Litz wire. Look it up to see what is claimed about the benefits. Some people say there is little benefit in using Litz wire compared to a single strand magnet wire or stranded hook up wire in a PI mono coil.
bbsailor
Do a web search on the words "Litz wire" and see the various strand configurations that wire vendors normally stock.
Litz wire is popular among ham radio enthusiasts and those who make crystal radio sets. Their coils are wound with Litz wire to obtain a higher "Q" factor (quality) than would be possible using plain magnet wire with a single core.
One of the Minelab patents on the patents section of the following web site: "http://www.thunting.com/cgi-bin/geotech/pages/common/index.pl?page=metdet&file=patents.dat" references Minelab Coils using Litz wire. Look it up to see what is claimed about the benefits. Some people say there is little benefit in using Litz wire compared to a single strand magnet wire or stranded hook up wire in a PI mono coil.
bbsailor
A
Anonymous
Guest
Thanks,I not school trained,low teck.some of my questions might sound dum.
I have made a fue coils, transformers, pp-motion induction moters,capacitors,etc.
I dont see any advantage in takeing multiple insulated magnet wire,to lower resistance in a coil.
When a pulseing current is present in Litz wire,it seems to me that each wire will act like a high speed capacitor and build up a small charge in each strand.unless minelab has a way of countering this.
I am low teck,I could be wrong. Thanks.
Frank.
I have made a fue coils, transformers, pp-motion induction moters,capacitors,etc.
I dont see any advantage in takeing multiple insulated magnet wire,to lower resistance in a coil.
When a pulseing current is present in Litz wire,it seems to me that each wire will act like a high speed capacitor and build up a small charge in each strand.unless minelab has a way of countering this.
I am low teck,I could be wrong. Thanks.
Frank.
A
Anonymous
Guest
Some forum PI experts, like Reg (search on his name for his work on coils using Litz wire), have reported a minimal benefit in using Litz wire.
If you wanted to build a high current coil that is also very fast, meaning less than 10uS from the tramsmit pulse turn off, then you might gain some small benefit by using Litz wire, since eddy currents can't flow between the individually insulated strands.
Also, the RF resistance of the coil will look a little lower to the magnetic pulse frequency since each conductor carrys a part of the signal on its surface. For a given cross section of wire, an equivalent Litz wire diameter (with multiple strands) will handle the pulses a little more efficiently.
Check some of Eric Foster's discussions about coils. He seems to cover this issue pretty well and also mentions Litz wire.
bbsailor
If you wanted to build a high current coil that is also very fast, meaning less than 10uS from the tramsmit pulse turn off, then you might gain some small benefit by using Litz wire, since eddy currents can't flow between the individually insulated strands.
Also, the RF resistance of the coil will look a little lower to the magnetic pulse frequency since each conductor carrys a part of the signal on its surface. For a given cross section of wire, an equivalent Litz wire diameter (with multiple strands) will handle the pulses a little more efficiently.
Check some of Eric Foster's discussions about coils. He seems to cover this issue pretty well and also mentions Litz wire.
bbsailor
A
Anonymous
Guest
Thanks, what you said sounds better than 1 stran of magnet wire.
Let me ask another low teck question on coil capacitance. it might help some-one else.
What is symptoms of two much capacitance in a coil.
GA- coil, is air gap.how much gap is to much,to relieve cap in coil.dont get to teck-enal.would the thick-ness of 2 peace of paper be about right.
Frank,
Let me ask another low teck question on coil capacitance. it might help some-one else.
What is symptoms of two much capacitance in a coil.
GA- coil, is air gap.how much gap is to much,to relieve cap in coil.dont get to teck-enal.would the thick-ness of 2 peace of paper be about right.
Frank,
A
Anonymous
Guest
Frank,
Given two coils with the same number of turns, the coil with the wire spaced farther apart will have lower capacitance and also have a higher self resonant frequency. All coils will resonate at some self resonance based on the inductance of the coil and the capacitance of the turns. One coil that I made used Kynar wire wrap, 30 gauge, 50 ft long, 18 turns at 10.5" diameter, had about 250uH inductance and self resonated at about 500kHZ.
The folks who make coils for crystal radios use a basket weave technique so that the turns do not run next to each other, thus reducing coil capacitance.
One way easy to reduce capacitance is to use regular hook-up wire with a plastic insulation. This insulation is much thicker than the insulation on magnet wire.
In addition to the capacitance of the coil; the capacitance of the shielded connecting wire; the MOSFET coil driver and the other internal circuit connections and the coil shield also add capacitance to the coil circuit, and tend to reduce the response speed of the coil.
Five feet of coil connecting wire has close to 100pf of capacitance. The MOSFET will 28 to 250 pf depending on the MOSFET device used. So as you can see, getting a fast PI response is not just in the coil. However, the coil is the easiest place to start to make changes and compare results.
bbsailor
Given two coils with the same number of turns, the coil with the wire spaced farther apart will have lower capacitance and also have a higher self resonant frequency. All coils will resonate at some self resonance based on the inductance of the coil and the capacitance of the turns. One coil that I made used Kynar wire wrap, 30 gauge, 50 ft long, 18 turns at 10.5" diameter, had about 250uH inductance and self resonated at about 500kHZ.
The folks who make coils for crystal radios use a basket weave technique so that the turns do not run next to each other, thus reducing coil capacitance.
One way easy to reduce capacitance is to use regular hook-up wire with a plastic insulation. This insulation is much thicker than the insulation on magnet wire.
In addition to the capacitance of the coil; the capacitance of the shielded connecting wire; the MOSFET coil driver and the other internal circuit connections and the coil shield also add capacitance to the coil circuit, and tend to reduce the response speed of the coil.
Five feet of coil connecting wire has close to 100pf of capacitance. The MOSFET will 28 to 250 pf depending on the MOSFET device used. So as you can see, getting a fast PI response is not just in the coil. However, the coil is the easiest place to start to make changes and compare results.
bbsailor
A
Anonymous
Guest
bbsailor,
Thanks, next coil I make,I try regular insulated wire and compair differance.
You were right about caps changeing speed of internal circuit.I am expermenting with each part in one of my PI to see what it Does.its a form of self school-ing.
I been raseing and lowering values and compairing differance. other day I change one,PI dept jumped from 12" to 16"+. right now its not use able.PI became loud unstable and sensitive.
Do you know how threshold works.What makes accural sound.
Where does sound come from.From audio IC, or last 2 op-circuits in PI.
This PI has no tune-able threshoid sound.it does have threshold gain.
To tune this PI,I turn threshold pot to where stacic noise is heard then go back to top of null.
Frank
Thanks, next coil I make,I try regular insulated wire and compair differance.
You were right about caps changeing speed of internal circuit.I am expermenting with each part in one of my PI to see what it Does.its a form of self school-ing.
I been raseing and lowering values and compairing differance. other day I change one,PI dept jumped from 12" to 16"+. right now its not use able.PI became loud unstable and sensitive.
Do you know how threshold works.What makes accural sound.
Where does sound come from.From audio IC, or last 2 op-circuits in PI.
This PI has no tune-able threshoid sound.it does have threshold gain.
To tune this PI,I turn threshold pot to where stacic noise is heard then go back to top of null.
Frank
A
Anonymous
Guest
Hi All,
I tried the equivalent Litz wire to the single strand 0.25mm Kynar insulated wire that I use in the Goldquest 11in coil. There was no measurable difference in performance, or in the receive waveform as viewed on a scope. It was only when I did some tests on "invisible nuggets" and shortened the delay to 5uS did Litz wire make any difference. A coil wound with the standard wire still worked at 5uS OK, but I was able to get down to 3.5uS, using the equivalent Litz.
Eric.
I tried the equivalent Litz wire to the single strand 0.25mm Kynar insulated wire that I use in the Goldquest 11in coil. There was no measurable difference in performance, or in the receive waveform as viewed on a scope. It was only when I did some tests on "invisible nuggets" and shortened the delay to 5uS did Litz wire make any difference. A coil wound with the standard wire still worked at 5uS OK, but I was able to get down to 3.5uS, using the equivalent Litz.
Eric.
A
Anonymous
Guest
the lowest pulse delay for a specific coil? What are the indicators to look for so you will know you are approaching that point?
Thanks
HH
Beachcomber
Thanks
HH
Beachcomber
A
Anonymous
Guest
I have noticed is it just stops detecting. The detector sounds OK in the headphones, but it just won't detect anything. Well almost anything. It still may pick up some real close items, but there's no doubt in your mind when adjusting to that point, it has been reached.
Mr. Bill <center><a href="http://www.surfscanner.com"><img src="/metal/html/s-s.jpg"></center>
Mr. Bill <center><a href="http://www.surfscanner.com"><img src="/metal/html/s-s.jpg"></center>
A
Anonymous
Guest
May-be you can tell me what happened here.
Last month I wound a 11" mono coil, no shield,useing magnet wire.while experminting with different damping resistors and checking dept with a US nickel.From 0 to about 10" air test,nickel was detected sharp and clear,10" up air test.there was a time delay.target was detected,you could count 1-2-3 before sound would stop.
Frank.
Last month I wound a 11" mono coil, no shield,useing magnet wire.while experminting with different damping resistors and checking dept with a US nickel.From 0 to about 10" air test,nickel was detected sharp and clear,10" up air test.there was a time delay.target was detected,you could count 1-2-3 before sound would stop.
Frank.
A
Anonymous
Guest
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