An antenna system is more easily interfaced to a radio when the input reactance at the feedline terminals is low or close to series resonance. If a center fed dipole is fed with a length of low loss balanced transmission line, the input reactance is a function of both transmission line length and antenna length, and to reduce the reactance at selected frequencies there are optimum lengths of dipole and feedline. The G5RV antenna design is an example of selecting these lengths to produce near-series resonances at amateur operating frequencies from 3.5-28MHz. There are other combinations of feedline length and dipole length which reduce the overall reactance as shown below. The red regions of Figure 1 have low RMS reactance over the frequencies shown to the right of the figure.