Different Length Dipoles Can Work, but They Work Differently

摘要

Q Del, AC7QS, asks: With all other parameters identical, what difference in performance might we expect between the usual half-wave-long horizontal dipole antenna and one that is 1 1/2 wavelengths long? Would it still be called a dipole? A I guess you could call it a dipoie, but it is different from the usual half-wave-long dipole in two ways: 1. The impedance, at resonance, of the 1 1/2-wave dipole is higher -around 100 to 150 Ω, depending on height. A half-wave center-fed dipole has a resonant impedance of typically 30 - 100 Ω, a better match for the usual 50 Ω coax, although the additional loss of an SWR of 2 to 3:1 is not usually a major issue in a reason- able length of coax on the HF bands. If of concern, the 3/4-wave dipole could be fed with 75 Ω or even 93 Ω coax and then transformed to 50 Ω at the station to match the impedance that the transceiver wants to see.