The solid line is gain as obtained directly from NEC2, calculated from the absolute value of the far field in the forward direction. The dotted line is the gain as calculated from the far field in the forward direction divided by the average far field. The dotted line includes ohmic losses. . Feed point impedance vs number of segments per element. Modified NEC2 for a 10 element yagi with 5mm elements on 144MHz.
Solid line is real part and dotted line is imaginary part.
The modified version of NEC2 is an improvement over the original program also for this 10 element yagi with 5 mm elements. The difference is small, but making a pre optimisation with only 3 segments per element may save time, and will be much better in the modified version. As a further illustration, look at these calculations of a single dipole, for which the length is selected to give a purely resistive feed impedance when calculated using 15 segments in original NEC2. Impedances Fig 5. The imaginary part of the impedance is a measure of the electrical length of the dipole.