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I'm in the process of planning a post-apocalyptic novel. The gist of it is that the vast majority (99.9%+) of all humans simply disappeared from the face of the earth, or so it seems. The story follows a group of survivors trying to find out if they're truly alone or if there are other groups to be found.

Let's assume that the internet and phone lines are down, but the power still works for now. Would it be feasible for the protagonists (located in North America) to both broadcast and receive intercontinental radio transmissions (to, let's say Europe)? If so, how could they go about doing it? Or maybe a radio transmission isn't the best option after all?

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    $\begingroup$ What do you know, there exists a large and active international community of passionate people called radio amateurs (or "ham radio" operators). They routinely make intercontinental connections with their home-based radio equipment. The practice of making very long distance connections is called DXing (pronounced dee-ecksing), and hams are known to exchange formal postcards (called QSL cards) attesting to exceptional interconnections, such as Bucharest to Melbourne. $\endgroup$ – AlexP Mar 27 at 21:42
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    $\begingroup$ Central power won't last very long. They'll need generators after a few hours to a couple days at most. Areas with hydro, solar & wind will last somewhat longer. Try not to be near a nuclear plant. $\endgroup$ – elemtilas Mar 28 at 1:35
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    $\begingroup$ @elemtilas: Whyever not? Assuming it has decent control systems and/or a few surviving operators, you have reliable power for decades. $\endgroup$ – jamesqf Mar 28 at 4:11
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    $\begingroup$ @elemtilas: No, there won't. At least if by "disaster" you mean the direct effects of a nuclear power plant failure, rather than irrational fear and panic exacerbated by government over-reaction. To get a nuclear power plant to fail in such a manner, you have to first design them very badly, then drive them into a failure mode, as happened at Chernobyl. $\endgroup$ – jamesqf Mar 28 at 16:56
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    $\begingroup$ @jamesqf: Not decades, not years, not moths, not weeks, a the very best a few days. More likely a few hours. The electric grid is not designed to operate without human supervision. When a powerplant feels insecure (not enough fuel, mismatch between energy production and consumption), if no human dispatchers and operators are there to take corrective action, the plant will shutdown. Other plants will react. The grid will first divide itself into small units (= "insularize"), then each separate island will shutdown. Nobody has ever seriously considered designing it to operate unsupervized. $\endgroup$ – AlexP Mar 28 at 17:26
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There is a well-established method of doing this, shortwave radio, also known as "High Frequency" or HF. Radio waves in the frequency range from 3MHz to 30MHz (10 to 100 metres wavelength) can be reflected from the "ionosphere", a layer of electrically charged atoms high in the earth's atmosphere. They can also be reflected off the earth's surface, including the oceans. This allows shortwave transmissions to reach anywhere in the world via a series of reflections back and forth between the earth and the ionosphere.

This isn't used for everyday broadcasting for several reasons, including:

  • It can reach anywhere in the world, which means another radio station using the same frequency anywhere in the world can interfere with it. Most kinds of radio broadcasting are only relevant to a limited area of the world, because of language and political boundaries, so using methods that can reach everywhere isn't useful.

  • The quality of speech and music is variable, but tends to be low. You're relying on the atmosphere to behave in the way you want, and it takes no notice of human concerns. Shortwave transmissions tend to work better at night, but that's not reliable. The earth's magnetic field, the solar wind, sunspots, and likely other things can affect shortwave, and there isn't much you can do about them. Switching to a different frequency can help, but this is not reliable, and gives your listeners a new problem, finding your station.

Shortwave is used for applications where you need long-distance communication without using infrastructure, such as undersea cables or communications satellites. This includes backup military communications, backup long-distance communication from ships and aircraft, international propaganda, spies being sent messages by their controllers ("numbers stations"), specialised kinds of radar, and amateur radio enthusiasts.

It's fascinating to get hold of a shortwave receiver and tune through the frequencies. You'll find a weird world of crackly speech in a range of languages, plus strange noises. The BBC World Service broadcasts on shortwave, as do many other national stations. Shortwave-capable receivers are available from any good electronics store.

This is the obvious and correct method for trying to find out if there's anyone else alive in the world. If you want to transmit, you need a radio amateur's equipment, and in a world where most people have vanished, the easy way to find that is to tour a city looking for a house with unusual antennas. Learning to use the gear is necessary, but an amateur will usually have manuals for their equipment, and more general books.

To research this properly, locate your local radio amateur, and explain what you're writing. They'll give you far more information than you need.

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    $\begingroup$ There many stations which broadcast on shortwave. For example, the BBC World Service. Radio sets capable of receiving shortwave transmissions are readily available in all fine electronics shops. $\endgroup$ – AlexP Mar 28 at 21:46
  • $\begingroup$ @AlexP: good points, added. $\endgroup$ – John Dallman Mar 29 at 10:03
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High frequency radio is used for world wide communications every day by HAM radio operators. Depending on the ionospheric conditions sometimes it is easy to make a contact sometimes it is hard is not impossible.

For Continuous Wave or CW also know as Morse code it can be easy to build a transmitter and a receiver as long a parts are available. Even voice communications is not too hard to make equipment for.

Assuming it was not a EMP type event it should be possible to find working radio equipment in most parts of the world. Most will run on simple 12 volt DC sources such as car batteries or solar panels.

Antennas can simple be section of wire of the correct length to be resonate at the frequencies you are using.

Typical HF frequencies are 1.7 MHz down to around 30 MHz. HAM do use higher frequencies but usually VHF, UHF and microwave are more or less line of sight and no long distances or DX as we call it.

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  • $\begingroup$ Even in the case of an EMP event, many amateur radio operators ("Hams") still adore and collect (working) tube equipment, which would be much less likely to be affected by an EMP event (if at all). Without "mains" power, operating this equipment would be more of a challenge... but never underestimate human (especially "Ham") ingenuity! $\endgroup$ – Hugh Buntu Mar 31 at 1:55
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Take over an AM Radio station. Hopefully it's running on remote.

This is probably not going to get you to Europe if the phone and internet is down but you can get a city, state, or even several states. If you're extremely lucky (plot) then it might be a station with a European following (I hear BBC on NPR).

If you really want to put some effort into it, get a boat, a searchlight, and check out Europe's coasts. There are a lot of cities next to rivers or the ocean, a good spotlight will be visible for 30+ miles and you're not depending on them to be listening in on a dead radio station.

https://en.wikipedia.org/wiki/Searchlight

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    $\begingroup$ No. Broadcast TV (like FM radio) is basically line of sight, maybe ~50 miles/80 km with a tall antenna. Your best bet for a commercial facility would be a high-powered (50 kW or so) AM radio station, if any still exist. Back in the 1970s and earlier, you could pick up e.g. stations in Texas from New England at night, due to skywave propagation: en.wikipedia.org/wiki/Skywave $\endgroup$ – jamesqf Mar 28 at 4:19

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