Radio: Difference between revisions

It is here that radio offers a valuable fallback technology for not only receiving critical status updates and information from local authorities and other communities, but also can allow for transmissions from your own community or group that can help you reach others and get needed assistance.

In an emergency where critical infrastructure is experiencing outage, local information will almost always be broadcast over AM (also referred to as Medium Wave) and/or FM. It is for this reason, at the least, a simple AM(MW)/FM radio with charged batteries and spares should be acquired and stored in an accessible place. They can usually be bought very cheaply. [[File:Am-fm-radio.jpg|thumb|left|A photo of 2 AM(MW)/FM radios, each with extendable antenna and headphone jack.]]

If you are caught out without a radio and have access to a vehicle, it very likely has a built-in AM(MW)/FM radio. Note that AM broadcasts travel over vastly longer distances than FM, and so it is important to be aware of this in relation to your geographical context. As always the best reception with radio is line-of-sight. While it is rare we can see the antenna(e) we are receiving a broadcast from, getting to a position of altitude away from RF (radio-frequency) occlusions like buildings and hills can make all the difference in reception.

[[File:Walkie-talkies.jpg|thumb|Two Baofeng BF-9700 Walkie Talkies]]

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.

If you are needing to split up your group, pre-arrange a signals plan such that group parties are not burning through batteries waiting for status updates throughout the period you are apart. That signals plan involves both agreeing on a channel and times or time-windows to be in contact. If the time is known to both parties throughout, specific times or windows of time can be agreed in advance. For instance, on a day long expedition beginning in the morning the expedition party may agree to send status updates at 10:30, noon, 14:30 and between 16:00 and 18:00 as expected range of arrival time. If clocks are not at hand for both parties, sun position will need to be used.

While not always easy, try to time your status updates from a position of high altitude. Signals will always be weaker in gullies, valleys, within dense foliage and in between tall buildings.

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|left|Image courtesy George H. Woodward (W1RN), https://arrl.org, taken from https://www.arrl.org/files/file/Technology/tis/info/pdf/0683033.pdf]]

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 3×10⁸ m/s (specifically 299,792,458 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.

[[File:Transceiver.png|thumb|A modern HF transceiver with a spectrum analyzer and DSP capabilities]]

An all-in-one transceiver is recommended for those with little technical knowledge. Most can be quickly learned reading their respective technical documentation. A more technical but in some cases less inexpensive option is discussed below.

In recent years, Software Defined Radio (SDR) has emerged as a practical and accessible alternative to dedicated hardware radio transceivers and receivers. Software Defined Radio implements a software interface to tunable radio hardware, such that reception and broadcasts can be done and processed entirely in software. This gives great flexibility to the operator, even so far as allowing for them to build their own tuners, signal de-modulators and broadcasting stations.