Single Layer Coil Design Chart
March 1955 Popular Electronics

March 1955 Popular Electronics Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged. articles from Popular Electronics.

Single layer coil design charts (aka nomographs) are a dime a dozen on the Internet. This nomograph appeared in a 1955 issue of Popular Electronics magazine. A couple examples of usage are included. The textbook Wheeler's formula for a single-layer coil with closely wrapped turns (wire diameter << coil diameter) is L = μ_r * d² * N² / (18 * d + 40 * l), where l has units of inches and L has units of μH. To verify one of the examples given in the article: L = μ_r * d² * N² / (18 * d + 40 * l),  = 1 * 5² * 19² / (18 * 5 + 40 * 0.52) = 81.45 μH, which is significantly less than the 100 μH given in the article. Another, more extensive Wheeler inductance formula (too long to reproduce here) yields 90.9 μH. Maybe I made a mistake somewhere, but I don't think so. I also downloaded the Coil64 software and plugged numbers into it and go similar results. I'm not saying the chart is wrong, just verify the results before relying on it. These are without regard to frequency.

Single Layer Coil Design Chart

This chart can be used to find inductance of a coil when dimensions and number of turns are known, or to find specifications to give a desired Inductance. Draw a line between either T and L or d and l/d, whichever are both known. Draw a second line between remaining known quantity and point of intersection of first line and unmarked vertical line. Extend second line to scale for unknown quantity and read answer.

EXAMPLE A: We have a coil 5" in diameter, 19 turns, 37 turns per inch, and wish to find the inductance. l = 19/37" = .52"; l/d = .52/5 = .104. Draw a line between d=5 and l/d = .104. Draw a second line from T = 37 through the intersection point to the L scale. Read the answer, 100 microhenries.

EXAMPLE B: We require the number of turns of a coil 5" in diameter, wound 37 turns per inch, to give 100 microhenries. Draw a line between T = 37 and L = 100. Draw a second line from d = 5, through the intersection point, to the l/d scale, and read l/d = .104. Then l = 5 x .104 = .52 Inches. The number of turns is .52 x 37 = 19, approximately.

Single Layer Coil Design Chart

Posted January 12, 2023
(updated from original post on 4/16/2013)