On VHF and higher frequencies, LPDAs are normally designed for a direct connection to a 50 or 75 Ω characteristic input impedance. ‡ Every so often, HF LPDAs are designed with a characteristic input impedance of 200 Ω a 4÷1 current balun transforms the impedance to 50 Ω.However, keeping element diameters the same throughout an LPDA turns out to be pretty forgiving in many cases. Cubical quad antenna calculator in java script let you calculate elements size and spacing in inch and meters. Includes design for 2 6 10 12 15 meter bands. In a true LPDA, element diameters should scale proportionally to element length. The cubic quad is a very popular way to get reasonably high gain and excellent front to back ratios as well as low angles of radiation for without going to extreme heights. Free-space directivity of a log-periodic dipole array as a function of its taper \(\tau\) and spacing \(\sigma\) for \(Z_\text\) of an LPDA is to a large extent determined by the dimensions of the shortest element.
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