Radio: Difference between revisions

This page introduces radio as a practical and reliable communications infrastructure for use in a situations and events where Internet access and mobile communications are not available.  

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 sometimes referred to as Medium Wave or MW) and/or FM. It is for this reason, at the least, a simple AM/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/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/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]]

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.  

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 radio is often 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 about 500 kHz to 13 MHz.  

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.

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 and FM 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 on 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>.

[[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.

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>.

[[File:Wavelength-calculation.jpg|thumb|left]]

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 12MHz, the full wavelength λ would be 24.98 meters (81.95 feet). From this calculation a fully functional 1/2 wavelength antenna of 12.5 meters (41 feet) could be built.

[[File:Transceiver.png|thumb|240px|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.

[[File:Rtl-sdr.jpg|thumb|left|Four RTL-SDR devices, two of them with the popular SMA style brass connectors, used to interface with antenna. Note the writing on pink tape on one citing that device's particular parts-per-million clock offset, referenced by the operator when preparing the device for use.]]

When working with RTL-SDR devices it is important to use a reference tone to determine the amount of 'clock shift' (in parts-per-million) that the device in use has, and shift it using your chosen tool before use. This is due to the lower quality of the clock (used to tune) on these devices. They will differ from device to device.

<references />