Run or download air-coil design software
Coil Design ...

Page 2, Cylindrical, Single-Layer, Air-Core Coils of Various Proportions

Author: R.J.Edwards G4FGQ © 13th May 2003

Continued from Page 1 ...

The computed self-resonant frequencies are generally accurate to within +/-7 percent and can be used in the design of short, helical, dipole antennas, such as a "slinky," in addition to the program's more serious uses.

When the test frequency exceeds the self-resonant frequency some computed data is invalid and a blinking warning is displayed. The coil's reactance is no longer inductive, but is capacitive and the coil has a very high-resistive impedance. Some applications, e.g., a resonant choke, make use of this effect. The program may be used to estimate the self-resonant frequency and impedance of a solenoid winding of coaxial cable for use as a choke-balun in an antenna feed-line. However, the self-resonant frequency may be slightly reduced by the coax-cable's pvc outer protective sheath.

Only whole numbers of coil turns are accepted by the program. For one-turn enter a coil length 1.031 times greater than proposed wire diameter and hit ratio = 1.

The program takes into account radiation loss in coils having dimensions that are appreciable fractions of a wavelength at the test frequency; e.g., a large loop.

The inductance of single-turn loops is computed within 2%, but due to transmission effects antenna designers are recommended to use the magloop4 program instead.

It is assumed that the Q value of self-capacitance and of insulating materials in the coil's immediate vicinity is 7000.

The method of calculating inductance for ordinarily-proportioned multi-turn coils has been adapted from Nagaoka. Computed values are accurate within 2 or 3 percent and are VLF values, i.e., not increased by coil self-capacitance.

A warning is displayed when the wire diameter is too large for the proposed coil diameter. This is best corrected by reducing the ratio of wire diameter to winding pitch. Pitch is determined by the entered distance between centres of adjacent coil turns.

Copper tube may be used for large-diameter conductors. Provided the tube wall thickness exceeds five times the RF skin depth the results obtained by this program will remain unaffected. The RF skin depth in copper is 2.1/Sqrt(F) millimetres, or 0.082/Sqrt(F) inches, where F is the frequency in kilo-hertz.

Note that the program can calculate the inductance of extremely coarse helices such as a single-turn of a long length of wire and small 'coil' diameter. It will be noticed the self-resonant frequency corresponds to a half-wavelength of wire.

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link Solnoid3 then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.

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