It gives you an idea of the change in wire length needed to move antenna resonance a specific number of KHz. This must be taken into account, and there are several methods of overcoming this.Use this chart as an aid in trimming the length of your antenna. If the antenna wire becomes too tight as the wind moves the tree back and forth, it could break the wire. If using a tree as a support, it must be remembered that the tree will move in the wind. A little thought and ingenuity will provide a number of different options. It is possible to erect the antenna in many places, using the supports that are available or that can be erected. How to Calculate VHF Radio Antenna Length There even may be another suitable building. Then another support may be a pole or even a tree. On the house it can be possible to attach the dipole to the chimney, or other high point. Often the supports may be a suitable point on a house and another support in the garden. The diagram above shows a typical installation for a ham band dipole antenna. The diagram above gives the basic format for the antenna, but in reality the antenna will need to be erected between two supports. The basic half wave dipole itself is quite straightforward, consisting of a radiating element half a wavelength long and fed in the centre. This means that a 40 metre dipole can also be used as a three half wavelength dipole on 15 metres. It is also possible to have longer lengths - antennas with lengths that are odd multiple of half wavelengths long also provide a low impedance. Also a dipole is most commonly found as a half wavelength dipole, although this is not the only length that can be used.įeeding the dipole at a high current point, as in the case of centre feeding a half wave dipole means that it is fed at a current maximum pint on the antenna.
#Quarter wave dipole calculator install#
The most straightforward way to install a dipole is as a horizontal antenna, although this is by no means the only way. Building the antenna and erecting it can provide a great insight into the aerials or antennas and how they work, and in this way the performance of the station can be enhanced even further. Wire, feeder, insulators and fixings are all that is required. Often the items needed can be salvaged from previous antennas, or bought for relatively small cost. A dipole antenna can be a very effective antenna, providing a good level of performance especially if it is erected as high as reasonably possible and away from obstructions, etc.īuilding am HF ham band dipole does not have to be expensive. Dipoles are widely used on bands like 80 metres, 40 metres, 20 metres, 15 metres and 10 metres where they can provide excellent levels of performance.
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