RF Coil Basics
As we know inductors and capacitors are the main components used in RF tuning circuits.
The resonant frequency of the tank circuit is determined by the following equation.
F = 1/((2*pi)*SQRT(LC))
From the above equation L and C can be found easily which will be
C = 1/(39.5*F2*L)
L = 1/(39.5*F2*C)
Capacitors of various different values are easily available but it is difficult to find inductors of your need. Hence people usually left with designing RF coil of their own.
RF coils fall under two categories air core coil and non air core coil. For non-air-core coils ferrite, powdered iron or toroid can be used as core material.
How to make RF Coil
Depending upon fixed or variable RF coil design suitable core need to be choosen and any conductor such as insulated thin copper wires are wrapped around the core.
Material of the core is selected based on the operating frequency. For variable inductor shielded slug tuned inductor form is used.
After determining the core, the next step for RF coil design is to determine number of turns (N) as per following equation:
N = 100 * (L/0.9*AL)0.5
Where, L is the inductance in µH
N= Number of turns
AL factor is function of properties of core material. AL value depends on frequency range of operation.
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