Reducing Capacitance on Coil Inductance

A capacitance is formed whenever two conductors are side by side. A coil produces capacitance as well as inductance because the turns are side by side. Unfortunately, with large multiturn loops, this capacitance can be quite large. The “distributed capacitance” of the loop causes a self-resonance with the inductance. The loop does not work well at frequencies above the self-resonant point, so it is sometimes important to raise the self-resonance to a point where it does not affect operation at the desired frequencies. 

Figure 15-13 shows a solution that raises the self-resonant point. The turns are broken into two or more groups and separated by a space. This method reduces the effective capacitance by placing the capacitances of each group of wires in series with the others.