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Added small section on Delta Loop Antennae
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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. | ||
==== | ==== 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 and have little resources and/or poor reception with a little handheld, even a rough 6 meters length of wire should give you opportunity to listen to many stations within an AM/MW range (about 500 kHz to 13 MHz). | 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 and have little resources and/or poor reception with a little handheld, even a rough 6 meters length of wire should give you opportunity to listen to many stations within an AM/MW range (about 500 kHz to 13 MHz). | ||
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If you are wanting to listen to broadcasts from popular amateur radio bands, which have far larger wavelengths (like 40M, 80M), you can try any very long wire you can get your hand on. Very long wires can allow for tuning across several bands, as the wire will include 1/4, 1/2 and perhaps even full wavelength representations. Using any long wire without a balun will often result in reception suffering from Standing Wave Ratio (SWR) interference due to differences in impedance between the antenna itself and the feedline to the receiver <ref>https://en.wikipedia.org/wiki/Standing_wave_ratio#Practical_implications_of_SWR</ref>. If you are without a balun, you can carefully select a wire for minimum interference. Physicists have studied random wire electromagnetic fields in relation to the SWR phenomenon, and with the aid of computer modeling have determined ideal lengths for minimal interference. An example is J. C. Sprott, a physicist at University of Wisconsin, USA<ref>https://sprott.physics.wisc.edu/technote/randwire.htm</ref>. | If you are wanting to listen to broadcasts from popular amateur radio bands, which have far larger wavelengths (like 40M, 80M), you can try any very long wire you can get your hand on. Very long wires can allow for tuning across several bands, as the wire will include 1/4, 1/2 and perhaps even full wavelength representations. Using any long wire without a balun will often result in reception suffering from Standing Wave Ratio (SWR) interference due to differences in impedance between the antenna itself and the feedline to the receiver <ref>https://en.wikipedia.org/wiki/Standing_wave_ratio#Practical_implications_of_SWR</ref>. If you are without a balun, you can carefully select a wire for minimum interference. Physicists have studied random wire electromagnetic fields in relation to the SWR phenomenon, and with the aid of computer modeling have determined ideal lengths for minimal interference. An example is J. C. Sprott, a physicist at University of Wisconsin, USA<ref>https://sprott.physics.wisc.edu/technote/randwire.htm</ref>. | ||
==== Delta Loop Antenna ==== | |||
The next step up in sophistication and technical challenge from a single straight wire antenna is a ''delta loop antenna''. It offers improved reception due to having far higher likelihood of matching broadcast polarity. It is quite easy to make, and can be suspended vertically from any high point, for instance affixed to the the peak of a roof, balcony or window and run down the front of the building. | |||
[[File:Delta-antenna-triband.jpg|thumb|320x320px|Example of a multi-band delta loop antenna design, here for the 80m, 40m and 30m bands. This file shared courtesy of Iulian Rosu (YVA3IUL), and as per the attribution in the image]] | |||
The sides of a delta loop antenna are equal and typically correspond to a 1/2 or 1/4 wavelength. Many designs are multi-band. | |||
==== Other wire antenna designs ==== | |||
A comprehensive source of designs can be found at the QSL hobby and amateur radio site<ref>https://www.qsl.net/va3iul/Antenna/Wire%2520Antennas%2520for%2520Ham%2520Radio/Wire_antennas_for_ham_radio.htm</ref>. | |||
==== Wavelength calculation ==== | ==== Wavelength calculation ==== | ||