28ga teflon wire

[RobN]

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.

[Qiaozhi]

28 gauge wire has a thickness of 0.32mm (you measured as 0.368mm), which is a little thin for a PI.
I presume your trying to make a fast coil using this method, and the spiral construction will help to lower the inter-winding capacitance. 29 turns sounds about right, so I would just wind it and see what happens, and (of course) report back here with the results.

[RobN]

Thanks, I sure will let you all know how it turns out.

[dbanner]

In looking at photo of the original surf pi coil, I took note of the spacing between the windings(pitch?). It looked to be roughly half the diameter of the winding itself(maybe more). This give me suspicion of some relevance to the optimal space between windings as half the diameter of wire. But who knows, very little information exists about spiral coil construction.
Do you have Coil32 calculator software? It is yet another coil calculator you can download for free. It has a spiral coil calculator which is very good and gives many parameters.
The White's coil has 42 turns. Which is of no relevance to your coil, just interesting to know.
Another observation is that the White's coil( I am assuming it's whites), the inner diameter looks to be half the outer diameter. This must have some significance, as the ratio is same as a standard concentric coplanar arrangement.

[dbanner]

Edited

[qute1]

hi robn you could use 2 or three strands (ends soldered together) of the thinner wire to improve the resistance (high on thin wires and thin litz) i use three strands on some coils just because of this added benefit have also found twisted pairs from cat 6 cable to work well too.

[green]

I used AWG28 solid magnet wire to wind a flat spiral coil, no added spacing. Fast coil but flat basket looked better at amplifier out, don't know why. Interested in how yours works.

[dbanner]

Green, I totally misread you table, the flat basket shows better performance.

[dbanner]

The difference in specs between the two coils( inductances, capacitance) seems quite small, only the SRF has a small spread, so have you drawn any conclusions as to why the flat basket perform a little better? Just a few puffs can make measured difference? I wouldn't have thought so.

[green]

The difference in specs between the two coils( inductances, capacitance) seems quite small, only the SRF has a small spread, so have you drawn any conclusions as to why the flat basket perform a little better? Just a few puffs can make measured difference? I wouldn't have thought so.

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.

[kt315]

In looking at photo of the original surf pi coil, I took note of the spacing between the windings(pitch?). It looked to be roughly half the diameter of the winding itself(maybe more). This give me suspicion of some relevance to the optimal space between windings as half the diameter of wire. But who knows, very little information exists about spiral coil construction.
Do you have Coil32 calculator software? It is yet another coil calculator you can download for free. It has a spiral coil calculator which is very good and gives many parameters.
The White's coil has 42 turns. Which is of no relevance to your coil, just interesting to know.
Another observation is that the White's coil( I am assuming it's whites), the inner diameter looks to be half the outer diameter. This must have some significance, as the ratio is same as a standard concentric coplanar arrangement.

absolutely bad and poor coil. not fastest. only trash.

[dbanner]

KT, it may not be the best, but it's far from the worst. There are few clues here to implement if I am making flat coil. The first is the pitch, the second is the inner diameter/outer diameter ratio( important for average depth and sensitivity to both large and small targets). I think with multiple strand Teflon, in a flat spiral coil with these ingredients would be superlative.
Only one way to find out.
Now can anyone say where Teflon multi-strand wire is best salvaged from? Is there a commonly known use for such wire? The local store doesn't have any. Seems a rare item in third world country.

[green]

absolutely bad and poor coil. not fastest. only trash.

What is the fastest coil?

[kt315]

FASTEST.

http://www.geotech1.com/forums/showt...l-for-baracuda

[Carl-NC]

Another observation is that the White's coil( I am assuming it's whites)...

Not White's, Tesoro Sandshark. Printed spiral has the drawback of higher resistance, which may not matter in some designs. Assuming 1oz copper, a 1mm trace width is roughly equivalent to 31.5 AWG. One improvement that Tesoro could make is to double-side the spiral. A double-sided printed spiral using 2-3 oz copper could make a dandy fast coil. Easy & exactly repeatable.