Wire diameter also has a marked influence on this as shown in the diagram.įor a half wave dipole the length for a wave travelling in free space is calculated and this is multiplied by a factor "A". It is found that the antenna end effect increases with frequency and it also varies with different installations. This serves to effectively lengthen the antenna.
More specifically, the antenna end effect results from a decrease in inductance and an increase in capacitance towards the end of the antenna conductor. The end effect results from the fact that the antenna is normally operating surrounded by air, and the signal is travelling in a conductor which is of finite length. There are several reasons for this and it means that an antenna will be slightly shorter than the length calculated for a wave travelling in free space as a result of what is lightly termed the "End Effect." While it is possible to calculate the length of the antenna very well, spurious effects can mean that the length may still need to be adjusted slightly fo optimum operation once it has been installed in the required location.ĭespite this, it is always necessary to calculate the required length and then if necessary be prepared to adjust it by a small amount to ensure the optimum operation Dipole length variation from free space lengthĪlthough the antenna may be an electrical half wavelength, or multiple of half wavelengths, this physical length is not exactly the same as the wavelength for a signal travelling in free space. In fact it is slightly shorter, even if only by a small amount. However it is found that the physical length of the dipole antenna is not exactly the same as the electrical wavelength in free space. Most dipole antennas are a half wavelength long, and accordingly it is often necessary to calculate the physical length of a half wavelength dipole antenna. Current and voltage waveforms on a half wave dipole showing the need to calculate the antenna length Often dipoles are designed to form a half wavelength at their operating frequencyĪs a result, calculating the length of a dipole antenna is a key element of designing and installing any one whether for HF, VHF, or UHF, etc., for broadcast reception, transmission or for two way radio communications, such as point to point links amateur radio, for reception or any application. The length of a dipole is the main consideration for determining its operating frequency. Dipole Antenna Length: calculation & formula Notes and details about the dipole antenna length calculation & formula for a half wave dipole.ĭipole antenna basics Current & voltage Half wave dipole Folded dipole Short dipole Doublet Dipole length Dipole feeds Radiation pattern Build HF ham dipole Inverted V dipole HF multiband fan dipole HF multiband trap dipole G5RV antenna FM dipole design
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