28ga teflon wire

[RobN]

Green, what is the resistance on that coil? I don't have 29 wraps on mine yet only 27 or 28 and the inductance is low but my resistance is already up to 3.3 I think it was.

[green]

For a coil with a 190MM or 7.5 inch inside dia, I've gone with 45.

45 is what I had with the above flat basket coil, 193mm I.D.

[6666]

Odd number, 1/2inch or 15mm spacing seems to work. 20mm might.


Poke 3 or 5 toothpicks, wind some wire around them back and forth. Try some different spacings and see what you think.

For a coil with a 190MM or 7.5 inch inside dia, I've gone with 45.

[green]

Made a spiral coil with AWG28 magnet wire to match RobN's coil specs. reply #1 to compare with Teflon coated wire. I'll shield it later.

[6666]

Odd number, 1/2inch or 15mm spacing seems to work. 20mm might.


Poke 3 or 5 toothpicks, wind some wire around them back and forth. Try some different spacings and see what you think.

Thanks will try it.

[green]

I have not finished the spiral coil with Teflon wire yet. My wire came up about 4 or 5 wraps to short and I have to solder another length of wire to it. Right now I am at 28 turns it's 250uH and at 3.3 ohms. Resistance is getting a little high ben better with larger dia. wire. Try to get back to it in a day or two.

crystalradio.net/professorcoyle/professorcoylespiderweb.shtml
Coil calculator I've been using. I got 330uH instead of 300uH the calculator calculates for the coils reply #43 if I'm measuring inductance right.

[green]

How many toothpicks do you use in your basket coil , thanks.

Odd number, 1/2inch or 15mm spacing seems to work. 20mm might.


Poke 3 or 5 toothpicks, wind some wire around them back and forth. Try some different spacings and see what you think.

[RobN]

I have not finished the spiral coil with Teflon wire yet. My wire came up about 4 or 5 wraps to short and I have to solder another length of wire to it. Right now I am at 28 turns it's 250uH and at 3.3 ohms. Resistance is getting a little high ben better with larger dia. wire. Try to get back to it in a day or two.

[6666]

Reason shielding didn't make it slower. I check resonance by exciting an operating PI with the test coil(hold it near operating PI coil)with scope connected to operating PI amplifier out. I connected the shield to circuit common instead of one of the test coil leads like I should have(test coil isn't connected to circuit common when checking for coil resonance, wasn't thinking). Including scope pictures of some repeat tests I did today. Wondering if I'm doing something else wrong. Picture flat radial_2 is where shield was connected to circuit common instead of one of the test coil leads. Added some scope pictures with test coils connected to Tx driver with and without a series diode(scope probe clipped to coil lead insulation to minimize added capacitance to the circuit). I calculate coil inductance by adding a capacitor across the test coil when checking for coil resonance. The 100nf capacitor measures 100.0nf on my better meter and 97.5nf on the other meter. The 10nf capacitor measures 10.4nf on both meters.

How many toothpicks do you use in your basket coil , thanks.

[green]

I'm just trying to learn. Have read spiral coil is fast but adding shield makes it slower than other winding methods, not what I've found. Most of the time I have more questions than answers. I don't know why the overshoot, looking like the coil is underdamped or why the overshoot is different between the two coils. The flat spiral has a lower circuit resonance maybe some of the reason.

Added lead length and Tx circuit capacitance are higher than coil capacitance.

Reason shielding didn't make it slower. I check resonance by exciting an operating PI with the test coil(hold it near operating PI coil)with scope connected to operating PI amplifier out. I connected the shield to circuit common instead of one of the test coil leads like I should have(test coil isn't connected to circuit common when checking for coil resonance, wasn't thinking). Including scope pictures of some repeat tests I did today. Wondering if I'm doing something else wrong. Picture flat radial_2 is where shield was connected to circuit common instead of one of the test coil leads. Added some scope pictures with test coils connected to Tx driver with and without a series diode(scope probe clipped to coil lead insulation to minimize added capacitance to the circuit). I calculate coil inductance by adding a capacitor across the test coil when checking for coil resonance. The 100nf capacitor measures 100.0nf on my better meter and 97.5nf on the other meter. The 10nf capacitor measures 10.4nf on both meters.

[Qiaozhi]

The only downside to this printed coil design is going to be the cost. In most cases It will be more expensive than the detector itself. For home builders of surf, bara minipulse etc. It will be very expensive. A less expensive option would be to just go with single layer spiral.

If you have access to a CNC machine, you could engrave an SRBP copper clad board as a much cheaper alternative.

[green]

Hi all, I am planning on building a flat spiral coil from 28ga. Silver plated stranded teflon coated wire. The wire specs are .0275 inch with insulation and all. Wire dia. Without insulation is .0145in which would leave a total thickness of .013 for the insulation. This is all measured with digital calipers and not by the data sheet of the wire.
i am going with a ID of 6.75” (just a piece of round plastic I had on hand to use as a die) and according to the flat spiral calculator I am using- 6.75”ID & 29 turns & wire dia of .0145 with spacing of .013 between each wire would be—
Inductance of 351.965uH
OD of coil 8.345”
total wire length of 687.623” (doesn’t show ohms) I will try other coil calculators to see what they say later. For now I just want some of your all opinions if this is even doable.
would this be usable for a Surf PI 1.2 (from what i have read on this forum for a surf PI the inductance should be between 300 to 350) please correct me if i’m Wrong.
Should I have bigger spacing between the wires?
Is the wire just to small to be useful.
I can add some small string between the wires to space them out more if needed.
Please any advise will be very, very helpful.

Have you finished the coil? Interested in how Teflon coated wire compares with magnet wire.

[dbanner]

Was checking avaiability of the PCB boards - most of them come rectangular. Very few suppliers offer 30x30cm which i gues will be the best size to start from. Also very few offer double sided boards sqare type.

The only downside to this printed coil design is going to be the cost. In most cases It will be more expensive than the detector itself. For home builders of surf, bara minipulse etc. It will be very expensive. A less expensive option would be to just go with single layer spiral.

[nonkapo]

Was checking avaiability of the PCB boards - most of them come rectangular. Very few suppliers offer 30x30cm which i gues will be the best size to start from. Also very few offer double sided boards sqare type.

[dbanner]

I think maybe the thickness of PCB board may slightly reduce inductance of overall dual printed coil, may need to add a couple of turns to compensate.
Curious to know what the measured inductance and SRF turn out to be.
It deserves its own thread.