Radio

Introduction

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.

The Internet and mobile networking are complex infrastructures dependent on a stack of technology for their function, from internet exchanges to routing and switching hardware, submarine cables, base stations and their antennae and a stable power grid. This complexity introduces multiple points of vulnerability. For instance, a flood could damage a power station, causing a black out that results in no Internet access at home nor mobile data, texts or calls via the cellular network.

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.

AM/FM radio reception

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.

A photo of 2 AM/FM radios, each with extendable antenna and headphone jack.

It is good to buy am AM/FM radio with a mini-jack socket and extendable antenna. The mini-jack socket allows for plugging in headphones which can be useful when reception quality is poor. The extendable antenna can greatly aid in finding and receiving a broadcast.

Small radios such as these can be put into a backpack or 'go bag', alongside a spare set of batteries. Rechargeable batteries should be used where possible. It can be a good idea to waterproof your radio by putting it in a quality zip-lock bag, alongside spare batteries held together with a rubber band or tape. Be sure you have tested it and have learned how to use it before you do.

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.

Walkie-talkies

Two Baofeng BF-9700 Walkie Talkies

Unlike AM/FM radios detailed above, walkie-talkies are both broadcast station and receiver, and so known as 'two-way' radios. The range of a modern walkie-talkie is anything from a few hundred meters in a city and in dense vegetation, to many kilometers when used on a peak or high rooftop. This communication tool can be especially invaluable when you are in a group and need to split up, staying in contact and relaying information.

Walkie-talkies operate on license-free broadcast frequency ranges in the UHF (Ultra High Frequency) band respective to the region the walkie talkie is purchased within. In the EU the allocation is known PMR446 (Private Mobile Radio, 446 MHz), whereas in the US it is typically the Family Radio Service (FRS) or GMRS, and in Australia UHF CB.

Regardless, if you are in a region using 2 or more walkie-talkies operating on unlicensed bands, they will still function, but may overlap with existing local broadcasts. Typically walkie-talkies include a channel selector for selecting a pre-agreed channel to operate on. This selector is either a button or dial. It is important to agree on a channel to use before splitting up your group and using the walkie-talkies. Some walkie talkies also include a radio scanner, allowing the operator to quickly find and tune into a local radio station. Some even include NOAA weather radio receivers.

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.

2-way communication guide

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.

In the event there is a basecamp or base with more than 1 other party working remotely, then all contact should go through basecamp rather than between parties directly. Important information is best written down first for clarity, and to minimise time spent using the handsets so preserving battery life.

Use the RSVP guide for 2-way communication :

• Rhythm - Speak at an even pace
• Speed - Talk slowly
• Volume - Speak softly
• Pitch - Speak at a higher pitch than normal and use the phonetic alphabet when spelling out names

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.

DIY Wire Antennae

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 .

Random Length Wire Antennae

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.

Wire antenna for AM 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 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.

The most common configuration for random wire antennae is to suspend it 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. If just using wire to affix to the structures, ceramic insulators can be added inline at each end, with the feedline to the receiver connected to the suspended antenna section. In the absence of proper ceramic 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. Alternatively, a solid piece of polyethylene plastic (for instance a dog chew toy, holes put at each end) can be used.

When the wire is short enough, it can alternatively be hung vertically from a roof or tree, and sometimes enjoy better reception as it will have closer polarity (electromagnetic orientation) to that of the broadcasting antenna.

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. If you do not do this, you risk destroying your equipment.

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. 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 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 . 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.

Delta Loop Antenna

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 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.

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.

Wavelength calculation

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 shown in the inline image.

Here, 'v' is called the phase speed (magnitude of the phase velocity) of the wave and 'f' is the wave's frequency. 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.

Receivers, transceivers and tuners

A modern HF transceiver with a spectrum analyzer and DSP capabilities

To work with specialist and custom antennae a receiver will be needed. Unless the antenna is built with precision to listen to a particular signal, a tuner will be needed. If broadcast is also desired, a transmitter will be required. In radio terminology, a device that both transmits (TX) and receives (RX) is a 'transceiver. Dedicated all-in-one transceivers can vary greatly in price and features, and depending on the region the operator is in, are bound to local broadcasting laws. Typically a HAM (Hobby and Amateur Radio) license is required to operate them.

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.

Software Defined Radio

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.

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.

Software Defined Radio is a large topic, and will not be covered in depth here. Should the reader be interested in exploring building transceivers in an SDR context, both the BladeRF and HackRF are interesting hardware options to look at. A comprehensive list of SDRs can be found here. SDRs are typically interfaced with GNUradio or another software radio programming environment. Every feature and facet of a modern dedicated hardware transceiver can be implemented in software on a laptop or workstation.

Radio enthusiasts in Aotearoa New Zealand listening to an AM radio broadcast from Austria, received on a 20M Full Wave Loop wire antenna connected to an RTL-SDR tuned by the GQRX software

An inexpensive option for those wishing to build a quality receiver for their long-range antenna project is working with RTL-SDR devices and compatible tuners. RTL-SDR devices are low-cost digital video tuner (DVB-T) USB sticks using the Realtek RTL2832U controller that can be repurposed for receiving a broad spectrum of radio signal.

Some RTL-SDR models will provide reception from 500 kHz up to 1.75 GHz. For those wishing to work with lower signals, for instance in the MW, an 'upconverter' can be used. A popular upconverter is the Nooelec 'Ham it up'.

The RTL-SDR project is maintained by a radio enthusiast group called Osmocom. RTL-SDR drivers exist for GNU/Linux, Windows and OS X, and can be tuned with several different popular interfaces. One of them, which is recommended for beginners, is the cross platform visual tuner and de-modulator GQRX.

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.

Offline networking with radio

Computer controlled radio platforms such as LoRaWAN can be used to provide for sending text and other data over a mesh network. Please see Offline Networking for more.