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→Random Wire Antenna
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[[File:Random-wire-antenna.jpeg|thumb|Image courtesy George H. Woodward (W1RN), https://arrl.org, taken from https://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf]] | [[File:Random-wire-antenna.jpeg|thumb|Image courtesy George H. Woodward (W1RN), https://arrl.org, taken from https://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf]] | ||
The length of a random wire antenna should correspond to the bands you wish to listen to, and should be at minimum 1/4 of the wavelength of the band at which you wish to receive. | The length of a random wire antenna should correspond to the bands you wish to listen to, and should be at minimum 1/4 of the wavelength of the band at which you wish to receive. | ||
==== Random wire antenna for AM/MW reception ==== | |||
In a disaster situation with no access to mobile data nor the Internet, and a handheld radio does not provide sufficient reception or is unavailable, AM/MW radio is a good first option. If you are wanting to listen for local shortwave (AM/MW) broadcasts, a 5.8M length of wire will give you opportunity to listen to many stations within the popular range of 505 kHz at 13.2475 MHz and from stations further away than can typically be reached with a small handheld radio (as shown above). This is probably your best option in an emergency situation with little at hand. | |||
A common configuration for random wire antennae is that of a wire suspended between a home (or shelter) and a tree or adjacent structure. A loop can be made in the wire, twisted tight, and paracord or rope used to fasten it to each end. It is important that the wire is electrically insulated from the structures it is tethered to. Paracord or rope can be covered in an insulating plastic at the points of contact with the wire. If just using wire to affix to the structures, ceramic insulators can be added inline. In the absence of insulators, a ceramic cup with a sturdy handle can be used, with each portion of wire twisted to each end of the handle and the cup horizontal. | A common configuration for random wire antennae is that of a wire suspended between a home (or shelter) and a tree or adjacent structure. A loop can be made in the wire, twisted tight, and paracord or rope used to fasten it to each end. It is important that the wire is electrically insulated from the structures it is tethered to. Paracord or rope can be covered in an insulating plastic at the points of contact with the wire. If just using wire to affix to the structures, ceramic insulators can be added inline. In the absence of insulators, a ceramic cup with a sturdy handle can be used, with each portion of wire twisted to each end of the handle and the cup horizontal. | ||
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If you know what frequency you need to tune into, you can calculate the full wavelength and build an antenna to match. The wavelength calculation is as follows: | If you know what frequency you need to tune into, you can calculate the full wavelength and build an antenna to match. The wavelength calculation is as follows: | ||
[[File:Wavelength-calculation.jpg|thumb]] | |||
Here, 'v' is called the phase speed (magnitude of the phase velocity) of the wave and 'f' is the wave's frequency<ref>https://en.wikipedia.org/wiki/Wavelength</ref>. In the context of radio, 'v' is the speed of light, or 3×10<sup>8</sup> m/s. For instance, if the desired emergency broadcast station was at 1650kHz, the full wavelength would be 181.69m, and so a 1/4 wave of 45.42 meter (149 feet) or 1/2 wave antenna of 90.84 meter (298 feet) could be built. | |||
== Citations == | == Citations == | ||
<references /> | <references /> | ||