of the conductor frequencies in the VHF, UHF, and microwave regions (Fig. 2-12). This
has the effect of greatly decreasing the total cross-sectional area of the conductor, thus
increasing its resistance and signii cantly affecting the performance of the circuit in
which the conductor is used. For example, skin effect lowers the Q of an inductor at
the higher frequencies, causing unexpected and undesirable effects. Thus many
high-frequency coils, particularly those in high-powered transmitters, are made with copper
tubing. Since current does not l ow in the center of the conductor, but only on the
surface, tubing provides the most efi cient conductor. Very thin conductors, such as a
copper pattern on a printed-circuit board, are also used.