![]() The overall length for the antenna should be about 150 cms, i.e. A tie wrap can be used to secure the centre point of the FM dipole antenna The length of wire which has not been split can then be used as the feeder for the antenna. One method of doing this is to use a tie wrap such as those available from most electronics components stockists. The centre should then be secured to prevent the cable opening out any further. To make up the VHF FM dipole antenna, first the cable should have the two insulated wires split back away from one another and opened out. For making our FM dipole antenna, we used some cheap speaker wire. This is convenient if a reasonable length is needed. One advantage of using mains flex is that when used as a feeder for radio frequency signals this type of wire is a reasonably close approximation to 75 ohm twin or open wire feeder. Connectors - if it is to be connected to coaxial cable.Ĭomponents required to make an FM dipole antenna.String or twine to secure the ends of the dipole to relevant fixing points (if required).Tie wrap - to secure the centre of the dipole and prevent the flex opening out beyond what is needed.Twin flex - twin mains flex is idea but we used some old speaker flex.To make the simple DIY FM dipole antenna, only a few items are needed. How to make the simple DIY FM dipole antenna design In this case the inner conductor of the coax is connected to one leg of the dipole and the outer conductor (braid) of the coax is connected to the other leg of the dipole antenna. However for this application, no noticeable degradation should be seen and the VHF FM dipole antenna should operate quite satisfactorily without one. ![]() the outer shield is connected to earth and the antenna is balanced. This is because coax is what is termed an unbalanced feeder, i.e. Strictly speaking a balun should be used when coax or coaxial cable is used. This can either be open wire / twin feeder, or coax can be used. In the diagram each leg of the dipole antenna is joined to the feeder. The basic design for the FM dipole antenna is shown below. This is quite a wide bandwidth to be covered by a resonant antenna such as the dipole antenna, but as it is only used for reception the performance at the band edges is not as important as if it were to be used for transmitting. The FM broadcast band extends from 87.5 MHz up to 108 MHz. The length of the dipole is determined by the frequency of operation. For a half wave dipole each leg of the dipole will be an electrical quarter wavelength long. The dipole antenna consists of two poles or parts. It may even be possible to make a simple FM dipole using items that may already be in a junk box, or in a workshop or garage. Instead for internal use the DIY VHF FM dipole can be made from commonly available materials and therefore the cost is likely to be minimal. If they are to be used for internal use, then there is no need to use expensive materials to ensure they are not affected by the weather. They may prove to be the ideal solution for an internal FM antenna, possibly in the attic or roof space, or they may be used when a temporary antenna is needed. They can be made in a variety of ways, and for minimal cost. It is quite easy to make a simple DIY FM dipole antenna. The FM dipole antenna is most likely to provide greatly improved reception over many other improvised solutions that may be used. Many Hi-Fi tuners and other radios have input sockets that will accept the input from a coaxial feeder, and where no external antenna is used, a dipole antenna can provide an excellent solution. One area in which dipole antennas are often used is for the reception of VHF FM broadcasts. Make an FM Dipole Antenna Design Details of a simple to construct DIY FM dipole antenna design that can be built easily and used for indoor reception of broadcast FM signals.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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