Litz wire size for coils

[green]

Try a 100 ohm resistor in series with a 1N4148 diode in stead of the 1M resistor and excite the coil with a 1khz square wave. Wasn't thinking about sapping the signal generator. Maybe start with a 1k resistor in series and turn the amplitude up slowly.

Tried the circuit in spice. The square wave should go +-, zero mean. With the 1p capacitor I would try 10mv/div on the scope. Think it should work. You have a few things to try.

[godigit1]

Thanks for your help everyone.
Ill be home next week and really cant wait to experiment. Learning the workings of the detector is just as addictive as using them. The natural progression of the hobby for me at least.
I will post my results when I get back in again.

Thanks again!
jim

[green]

Some preliminary testing of the coils I have wound. Need to wind the other coils. Coil resonance with no lead wire. Was surprised the vertical coil(single layer solenoid) looks better than the vertical basket. Inductance lower than I had planed but should allow earlier sampling to see coil wire eddy currents. All coils 23 turns.

[6666]

Some preliminary testing of the coils I have wound. Need to wind the other coils. Coil resonance with no lead wire. Was surprised the vertical coil(single layer solenoid) looks better than the vertical basket. Inductance lower than I had planed but should allow earlier sampling to see coil wire eddy currents. All coils 23 turns.

Thanks,
very interesting
its a pity Aziz is no longer on the forum , he could give some visualisations of field strength etc.

[6666]

~~~~~~~~~~~~~~~~~~~

I use an LC200A purchased on Ebay for about $35, made in China of course. It seems to be pretty good in accuracy when compared to some old Dale Electronics (Now Vishay) coils I have.

Dan

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.

[baum7154]

I'm glad it is working for you and the price is pretty good too.

Dan

[green]

Added the Litz coil to the chart. Need to do some recording to see if I can see the wire eddy currents before I add any more coils. I like to guess what the test will show before I do it. I had recorded the TC of AWG12,19,24 solid wire. They plot close to a straight line on a log-lin chart. AWG28 charts a TC between .2 and .3usec. Depending on Rd that might be close to L/Rd TC. Maybe the AWG28 will show in the no target decay. Maybe the chart doesn't mean anything but gives me something to make a guess.

[Chet]

Hi Green


Litz wire is most effective below 1.4 MHz. When the coils have damping resistors connected the frequency will drop below 1.4 MHz. it will be interesting to see how Litz compares with solid wire coils with proper damping resistors connected. It will also be interesting to see how different AWG sizes and time constants effects early sampling. Thank you again for your great work.


Have a good day,
Chet

[Chet]

Hi Green
After second thoughts; the damping resistor is not the reason for the frequency drop. I should have said that the frequency will drop below 1.4MHz after the coil shield and three feet of coax or twisted pair capacitance is added to the circuit.
Have a good day,
Chet

[green]

Added the Litz coil to the chart. Need to do some recording to see if I can see the wire eddy currents before I add any more coils. I like to guess what the test will show before I do it. I had recorded the TC of AWG12,19,24 solid wire. They plot close to a straight line on a log-lin chart. AWG28 charts a TC between .2 and .3usec. Depending on Rd that might be close to L/Rd TC. Maybe the AWG28 will show in the no target decay. Maybe the chart doesn't mean anything but gives me something to make a guess.

Charted coil A(AWG28, coil D(AWG24) and coil E(175/46 Litz). Looks like AWG28 and AWG24 are acting as a target for a short time. Charted target recording minus no target recording. Mosfet gate driver triggers zero time.

[Chet]

Hi Green
Looks like the Litz coil is capable of sampling 1 to 2 microseconds earlier. It will be interesting to see how the coils compare on very small targets.
Thank you for the great work,
Chet

[6666]

Charted coil A(AWG28, coil D(AWG24) and coil E(175/46 Litz). Looks like AWG28 and AWG24 are acting as a target for a short time. Charted target recording minus no target recording. Mosfet gate driver triggers zero time.

Thanks what wind are you calling spider web ?

[green]

Thanks what wind are you calling spider web ?

picture

[green]

Hi Green
Looks like the Litz coil is capable of sampling 1 to 2 microseconds earlier. It will be interesting to see how the coils compare on very small targets.
Thank you for the great work,
Chet

All could be sampled with a 5 usec delay. If they were shielded and had a longer cable the minimum delay might be greater than 5 usec for all. Would there be a difference then?

[6666]

picture

Thanks its good to be clear on these things, sometimes the wind in your picture is called flat basket wind, interesting that the PVC wire has the highest SRF.