Funcţie de natura materialului din care este confectionată, antena nu se comportă ca un model ideal, lungimea sa electrică necorespunzînd exact lungimii fizice; de exemplu, un fir de 20 m lungime nu va oscila în λ/2 pe o lungime de unda de 40 m, ci, în realitate, în jurul lungimii de undă de 42 m, datorită aşa-ziselor „efecte de capăt” la izolatoarele terminale, care provoacă o „alungire electrică” a conductorului de circa 5%.
Pentru a obţine rezonanţa pe lungimea de undă de 40 m (7,5 MHz), lungimea antenei în jumătate lungime de unda (λ/2) se determină cu formula
L = 143 / f
în care L = lungimea de undă în metri, iar f = frecvenţa în MHz, şi vom găsi lungimea de 19,06 m.
În acelaşi mod, lungimea fizică a unui conductor oscilînd în sfert de lungime de undă (λ/4) poate fi calculată din formula L = 71,5/f.
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