File:Spider coil.jpg

English: A spiderweb coil, a type of air core inductor used as tuning coils in radio receivers. At radio frequencies, energy losses in ordinary coils increase due to proximity effect; the magnetic field of adjacent parallel turns of wire causes the current to concentrate in a thin strip next to the adjacent wires. So only a small portion of the wire's cross section carries the current, increasing resistive losses. In addition the adjacent turns of wire act like the plates of a capacitor, giving the coil significant parasitic capacitance. The spiderweb construction method reduces these effects by winding the wire in a flat spiral, so a given wire turn only has a few adjacent wires. In addition the wire alternates on either side of the form, providing more separation between adjacent turns. The number of tabs on the form is odd, so successive turns end up on opposite sides of the form.