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When selecting a walkie-talkie it is good to ensure it has a high IPX water rating, is durable, has a 'squelch' function (allows for 'cleaning' up a noisy signal to hear it better), good battery life and has at least 3W of power. Importantly, some walkie-talkies can only be charged in a special charging dock, and so if you choose a walkie-talkie of this sort it is important that it has removable batteries such that you can bring pre-charged batteries with you. If not, it is good to get walkie-talkies that take AA batteries, that you can recharge in a standard battery charger, one of which may include a portable solar charger. | When selecting a walkie-talkie it is good to ensure it has a high IPX water rating, is durable, has a 'squelch' function (allows for 'cleaning' up a noisy signal to hear it better), good battery life and has at least 3W of power. Importantly, some walkie-talkies can only be charged in a special charging dock, and so if you choose a walkie-talkie of this sort it is important that it has removable batteries such that you can bring pre-charged batteries with you. If not, it is good to get walkie-talkies that take AA batteries, that you can recharge in a standard battery charger, one of which may include a portable solar charger. | ||
== Random Wire Antenna == | |||
While far more efficient antenna designs exist, when long range reception is urgently needed, a simple but powerful antenna can be quickly built using shielded or un-shielded copper wire. Such wire can be a single core of common electrical wire used to wire a home, or any copper wire thick enough to withstand the strain of being strung taut between two points. Of all the wires, copper-clad steel wire between 1.6 to 2.0 mm is best however <ref>https://en.wikipedia.org/wiki/Random_wire_antenna</ref>. | |||
[[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. As a quick reference, 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. | |||
Random wire antennas are ever at risk of electrical storms, and so such an antenna should be electrically grounded. For this exposed metal plumping pipe can be used, or a steel stake driven deep into the ground. | |||
[[File:Homemade_balun.jpeg|thumb|Homemade 1:1 balun using a toroidal core and coaxial cable. This simple RF choke works as a balun by preventing signals passing along the outside of the braid]] | |||
At the receiving end of the random wire antenna, a ''balun'' is ideally used. A balun 'balances' an unbalanced line, significantly improving reception quality and mitigating for many Standing Wave Ratio (SWR) challenges, typical of long lines of wire used in a radio context<ref>https://en.wikipedia.org/wiki/Balun</ref>. Baluns can be made using a simple toroidal core commonly harvested from electronics at hand, or a professional balun can be purchased suitable for the project. | |||
=== Random wire antennae for hobby and amateur radio bands === | |||
During emergencies hobby and amateur radio (HAM) bands can be a source of valuable information. Radio operators operating in their homes or 'radio shack' may send broadcasts on popular 20M, 40M and 80M bands. These are long-distance bands, sometimes covering hundreds or thousands of kilometers, and so this should be kept in context when seeking information. It is also important to beware the operators of these bands are not necessarily providing authoritative situational status information. For this reason, AM/MW bands should be the preferred choice for reception when mobile data and Internet connectivity is not possible. | |||
If you are wanting to listen to broadcasts from popular amateur radio bands, with 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. However, reception will likely suffer from interference due to a phenomenon known as Standing Wave Ratio (SWR) 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>. Physicists have studied random wire electromagnetic fields and with the aid of computer modeling have determined ideal lengths for minimal interference. J. C. Sprott, a physicist at University of Wisconsin, USA, has calculated the optimal lengths for reception of the most widely used bands of 1.8-2, 3.5-4, 7-7.3, 10.1-10.15, 14-14.350, 18.068-18.168, 21-21.45, 24.89-24.99, and 28-29.7 MHz<ref>https://sprott.physics.wisc.edu/technote/randwire.htm</ref>. | |||
A summary table produced by Sprott follows. | |||
== Citations == | == Citations == | ||
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