Litz wire size for coils

[Chet]

Hi Green
Good test and good information. How much space is there between the coil and the painted surface?
Thank you,
Chet

[green]

Hi Green
Good test and good information. How much space is there between the coil and the painted surface?
Thank you,
Chet

The craft foam is about 2mm thick. The painted surface is touching one side of the foam and the coil the other side of the foam so about 2mm.

[Chet]

The craft foam is about 2mm thick. The painted surface is touching one side of the foam and the coil the other side of the foam so about 2mm.

Hi Green
Your results are sure much better than the copper screen that I have used in the past.
Thank you again,
Chet

[green]

Was looking at target decays today with the bench PI . Put one of the coils I used for the Litz wire test over the test coil and saw resonance at amplifier out. All the test coils resonate closer to 4MHz than the 2.5MHz I get with my resonance tester(coil in series with a 1N4148 and a 2N3904 transistor switched on and off). I didn't think the diode would cause resonance to lower that much. Could it or is placing the coil over a operating PI circuit not giving me a true resonance? I don't have a signal generator to excite the coil to try measuring that way.

[Chet]

Was looking at target decays today with the bench PI . Put one of the coils I used for the Litz wire test over the test coil and saw resonance at amplifier out. All the test coils resonate closer to 4MHz than the 2.5MHz I get with my resonance tester(coil in series with a 1N4148 and a 2N3904 transistor switched on and off). I didn't think the diode would cause resonance to lower that much. Could it or is placing the coil over a operating PI circuit not giving me a true resonance? I don't have a signal generator to excite the coil to try measuring that way.

Hi Green
Maybe you are seeing harmonics. Otherwise the coil capacitance would have to be a little less than 5 pf to get as high as 4 mHz.
Have a good day,
Chet

[green]

Hi Green
Maybe you are seeing harmonics. Otherwise the coil capacitance would have to be a little less than 5 pf to get as high as 4 mHz.
Have a good day,
Chet

You might be right. Including scope picture. Coil F connected to PI, coil H open circuit over PI coil. 6.8pf With the capacitance that low, maybe the diode or the capacitor coupling to the scope(twisted wire) might lower the resonance that much with my resonance tester.

[Chet]

Hi Green
It doesn’t look like harmonics. 6.8pf sounds reasonable. Try two diodes in series it may cut the diode capacitance in half.
Have a good day,
Chet

[green]

Hi Green
It doesn’t look like harmonics. 6.8pf sounds reasonable. Try two diodes in series it may cut the diode capacitance in half.
Have a good day,
Chet

Some tries, start resonant frequency(2.6MHz). (#1) Replaced twisted wire coupling capacitor with a 3.3p capacitor, frequency lowered (2.3MHz). (#2) lifted diode and resistor(limits current) from board, twisted wire frequency increased to over 2.9MHz. The two diodes didn't do much. Forgot to mention series resistor in reply #109. Coil in series with a resistor, 1N4148 and 2N3904 switched on and off. Couldn't get the resonance up near the 4MHz I get placing the coil over a operating PI(Reply #109). Would like to know if placing the test coil over a operating PI is a more accurate way to measure true resonance. Probably doesn't matter since the frequency is a lower after shielding and connecting to the Tx circuit.

[ODM]

Is your input amp oscillating? Doesn't have to be sustained oscillation, just resonance. A gimmick cap across the feedback resistor should show a change if this is the case.

[green]

Is your input amp oscillating? Doesn't have to be sustained oscillation, just resonance. A gimmick cap across the feedback resistor should show a change if this is the case.

Two stage amplifier. First stage feedback(20k,3.3p) Second stage feedback(15k,3.3p) Would another 3.3p across first stage work? Including some scope pictures. The resonant frequencies for the coils are close, but they were close with the resonance tester also.

[Chet]

Hi Green
I just ran two tests on a spider wound 295uH coil with no cable attached. Using a signal generator inductively coupled by a small 3 inch 4 turn coil. Then with a PI detector placed under the coil. Both tests resulted in a self-resonant frequency of 1.8 mHz. This works out to be approximately 26pf of coil capacitance. The scope probe was not connected; just laying outside of the winding.
Have a good day,
Chet

[green]

Hi Green
I just ran two tests on a spider wound 295uH coil with no cable attached. Using a signal generator inductively coupled by a small 3 inch 4 turn coil. Then with a PI detector placed under the coil. Both tests resulted in a self-resonant frequency of 1.8 mHz. This works out to be approximately 26pf of coil capacitance. The scope probe was not connected; just laying outside of the winding.
Have a good day,
Chet

Hi Chet
Thanks for the reply. Wasn't thinking about placing the scope probe next to the coil to check resonance, (KISS) The resonance was higher than I was expecting, inductance less than 300uH was some of the reason. Calculates about 7pf. Looks like a good way to measure coil resonance.

[6666]

My LC200A arrived today, seems like a nice meter,
it gives better inductance value readings to more decimal places, my other meters tend to round off the values in units of ten
and the fly leads are handy, no instruction sheet, so no idea what the usb cord is for, runs quite happily on 4 AA's.
thanks Dan for the tip.

Not impressed with the LC200A, it gives inductance readings way above the real value, when measuring my TDI and Minelab PI coils which are supposed to be about 300uH
my other meter reads closer to 300uH, were the LC200A reads about 400uH.

[baum7154]

Are your coils just the wire with no other components in them? Are they specified with or without their feedlines attached? Do you have a coil you made using the coil calculator for a specific value that is not shielded or enclosed to get an idea how close it comes to the calc value?

Just my thoughts

Dan

[green]

[QUOTE=6666;220230]Not impressed with the LC200A, it gives inductance readings way above the real value, when measuring my TDI and Minelab PI coils which are supposed to be about 300uH
my other meter reads closer to 300uH, were the LC200A reads about 400uH.[/QUOTE

Hi 6666

If you have an oscilloscope to measure frequency decay and a multi meter to measure capacitance and would be interested in trying to calculate inductance with frequency decay and capacitance to compare with your meters I would be interested in the result. I have a 10nf cog ceramic cap that measures 10.3nf and a 100nf polypropylene that measures 99.9nf that I use. Inductance calculates very close to the same using either cap. Don't know if decay frequency is enough different from resonant frequency to matter. Place scope probe near test coil, connect a capacitor(10nf to 100nf) to multi meter and record capacitance, connect capacitor across test coil leads, excite coil with an operating PI detector, measure decay frequency with scope. Inductance=.02533/measured capacitance/decay frequency squared. More complicated than connecting to an inductance meter but since I don't have one it's a way to measure inductance. Don't know how accurate it is but it would give you a number to compare your meters against.