Sevick’s books on inductors are widely regarded as the canonical works on inductors. I’m looking for a more intuitive understanding and not so much math. Here are some rules of thumb for inductors. Not everything here is necessarily 100% accurate. (That is the nature of a rule of thumb.)

Terms:

• Z: impedance in ohms
• F: frequency in Hertz
• L: Inductance in Henries
• k is a constant
• A = area of a turn
• N = number of turns
• C = capacitance

Formulae:

• Formal: The formula for inductance is: L = kAN^2
• Formal: For a simple choke (not at resonant frequency): Z = 2πFL
• Quasi-formal: For a choke at its resonant frequency Z, you treat it as parallel L and C. Z = 1/(impedance_of_L - impedance_of_C)

Informal

• Increasing the diameter of turns, adds reactance.
• Adding a turn, adds reactance.
• An inductor has reactance (lots), resistance (little) and inter-turn capacitance (little).
• Because an inductor has an L and a C, it has a resonant frequency.
  • Look up the resonant frequency in the ARRL Antenna Handbook or online. It is hard to calculate.
  • Often, you want the operating frequency to be well below the resonant frequency.
• The windings of the inductor are usually kept well apart; often several conductor diameters.
• A “W2DU balun” is just a bunch of ferrite beads (toroids) slipped over the coax feed line. If you need to choke a wide bandwidth, you can use a mix of ferrites to cover the range. Might need lots of beads an low frequencies.