📡 Radio From Scratch

Ferrite Rod (Solonoid) Antenna Calculator

Ferrite Rod Antennas, or more generally solonoid antennas, consist of wrappings of insulated wire around some rod.

The inductance of the resulting antenna can be calculated based on the inner “core” material used in the rod, as well as the number of wrappings of wire. If you are building a radio receiver, you may wish to first look at the [LC circuit calculator] to calculate your desired inductance.

Ferrite is a popular core material, as it is able to achieve much higher inductance than the equivalent antenna which lacks the core. Here is an example of a ferrite core frequently used for diy radio.

The formula that describes the inductance of this solonoid or wrapped antenna is:

$$ L = {{\mu N^2 A} \over l} $$


  • \( L \) is the resulting inductance in Henries
  • \( \mu \) is the permeability of the core. This is often reported as a relative permeability compared to Air. For Air, this is ~\(1.26 * 10^{-6} \). For iron/ferrite cores, this is ~200 times the value of air. A more complete listing can be found on wikipedia.
  • \( N \) is the number of turns, or wrappings of the wire around the core.
  • \( A \) is the cross section of the loop inside the wrappings.
  • \( l \) is the total length of the wrappings, measured along the rod.
Relative Permeability (times air)
Number of turns
Cross section area, in \( cm^2 \)
Length in cm
Inductance in Henries

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