What would be needed for radio broadcasts to be a viable means of communication in a post-apocalypse?

Question

The post-apocalypse in question is one where monster-like creatures have taken over most of the world. Now, twenty to thirty years later, only a few clusters of humanity still remain with somewhat functioning governments, and with "towns," as in places with apartments/buildings that have barely functioning water and electricity and other necessities that people live in, that are scattered across what's left of America.

What I want to know is what these "towns" would need in order to have radio broadcasts be a viable means of communication between members of the government to the public in pseudo-PSA announcements and also be used for their police force to communicate with each other through some kind of walkie-talkie like device. Also, if possible, a reason why it would be difficult if not impossible for said towns to communicate with each other. From the tech you would need to the infrastructure, what would it take for this post-apocalyptic world to have radio broadcast be an actual possibility?

Answer 1

In some ways radio's are a 1920's era technology. (Radio waves discovered in 1886, commercialized by 1900, widespread use by the 1920's, spark gap then AM radios first, followed by the FM radio being invented in 1933, then cellular radio's taking off for mobile communications in the 80's leading to the 2G,3G,4G, and now 5G, Satellite comms. etc.)

What is hard is higher bandwidth, higher frequency communications.

You can probably play with the elements of analog communications vs digital communications, or low frequency vs high frequency, as well as the weather and atmospheric effects, and the availability of electricity, off of each other in interesting ways.

Perhaps in your case, you don't have the industrial base to do high speed electronics, but being able to do lower frequency communications AM communications that can be picked up by a crystal radio with a long wire is still pretty easy.

Broadcasting one-way from government to the people might be O.K., but somewhat difficult if the monsteror wind knocks over the big antennas etc. Unreliable electricity is a problem - to broadcast long distances it helps to have a powerful transmitter, most towns have a few stations that put out 50,000 watts. In general it would be harder for people to have transmitters than receivers.

Voice is low bandwidth. For plain old telephone systems you only needed a little more than 3000 HZ. A very crude rule of thumb is that a digital communication system can have about needs about a bit per hertz. So if you wanted to broadcast a lot of data from one town town to another that might be hard to do, but talking might be o.k.

Higher frequencies are also more line of sight, and so would tend to be short range.

Lower frequencies also bounce off the ionosphere and are ducted/bounced around in somewhat unpredictable ways due to the weather and atmospheric conditions, but can be very long range. If you talk with some Ham radio operators, there is a whole subculture devoted to finding stations from around the world. So the range at which your characters can talk, when they can talk, and what resources they have to talk has a lot of room for the imagination.

Walkie-Talkies are a little bit harder to think through. If integrated circuits are rare or not availible, and vacuum tubes are required, then the radios would be bigger and heavier. Batteries are always a problem, can be heavy and don't last a long time. Kind of like WW2 and Vietnam era movies, mobile radios might be more like a backpack than a walkie-talkie.

If there is digital signal processing, then the radios can be very smart - there is an emerging field called software defined radio where rather than having circuits and knobs tune the frequency, and define the modulation format it is largely done in software. These radios if the chips were availible and there were some pretty good batteries could work pretty well. However they would be limited in range.

Don't forget, there is still a lot telephone wire, and fiber optic cable buried all over the place, that might interesting to try to find uses for. As well as that satellite that might still be in orbit that a good radio operation can still tell is in operation.

Answer 2

I don't know about transmitters, so I'll skip those.

Receivers are easy

Soldiers during WW2 would commonly make their own radios using whatever they had lying around in their foxholes.

Interference keeps transmissions local

We use radio because radio wave frequencies aren't readily absorbed or interfered with by the atmosphere. So change the composition of the atmosphere. Clouds of metallic particulates are at a low enough concentration to not cause serious health problems (at least, not to people wearing masks) but generate enough interference that the effective range of the radio is significantly reduced. You'll need to work out how this particulate metal got there (and is kept there).

Answer 3

Radio broadcasting and receiving is easy

There are over 15,000 radio stations in the United States (15,330 according to Google), and millions of radio receivers in cars, houses and people's hands that can receive their signals. Then add in the ham radio community, the police and emergency services radio networks, CB (citizens band) radios/walkie talkies and military radio equipment and there will be vastly more radio equipment than a few remaining clusters of humans could possibly need. (Each area will need to standardise on a set of equipment that works on the same frequency - unmodified civilian radios will not receive military frequencies and vice versa - but with lots of hardware available that is not really an issue.)

The problem 20 to 30 years post-apocalypse will be batteries for portable equipment. Non-rechargeable batteries will typically last less than 5 years in storage. Even a carefully maintained rechargeable battery will be marginal at maintaining any charge after 10 years. Large wet cells (something like a car battery) could be made relatively easily from scavenged materials, so radios could be operated in buildings or vehicles (if there are working vehicles) but hand-held walkie-talkies would be a big ask. (Definite image in my mind of a tiny radio receiver the size of a matchbox hooked up to an improvised wet-cell bank made up of 20 litre buckets.) If the government is transmitting AM at sufficient power and the citizens just need receivers then a crystal set requires no power at all, what it does require is many metres of fixed antenna.

Preventing long-range communication is much harder. There are people who do this for a hobby in the amateur radio community and there is still military equipment around for this purpose even since communication satellites became more prevalent. There are two simple approaches to long-range radio communication:

1. Elevated antennas and/or retransmission stations to extend the line of sight range for VHF and higher frequency transmissions; or
2. HF transmissions using long wavelengths that bounce off the ionosphere.

Option 1 can be stopped by the monsters relatively simply - the monsters can make it too hazardous to maintain retransmission stations, can attack balloons that are lifting antennae aloft etc. Stopping HF transmissions is much harder - HF wavelengths are metres long, so direct interference requires something like chaff, but the pieces of mylar, foil or whatever would need to be metres long and in exactly the right position to absorb the signal. Particulates in small quantities, as suggested by Ton Day, will have no effect on HF. The monsters cannot actively interfere with the signals unless they are either using very powerful transmitters of their own or are absolutely massive and have portions of their body that are adaptive antennae varying in length between about 4 and 40 metres and are naturally scanning for signals in a broad band all the time and either attack any source of HF signals (but not VHF!) or can adaptively jam the transmissions.

There are two slightly more plausible reasons why HF communications between distant communities would not happen. The first is prioritisation of resources - communities are so short of resources that they cannot afford to keep someone dedicated to monitoring the HF bands and/or powering the receiver (and possibly scanner - see below). Unless the distant communities are coordinating activities (eg trade) or providing immediately useful information then the leaders of the community may see this as having no benefit. The second possibility is that in a small community there will only be a few people who will understand antenna theory and all the other complexities of HF communication - if these people are casualties then the necessary knowledge will be lost. (Setting up HF antennae and equipment is much more complicated than the "push to talk" process for using short range radios.)

In summary:

• Short range public service announcements to fixed (house) radios in a town - easy.
• Walkie-talkies for people in the town - no, vehicle or maybe a big backpack unless you have a production line for batteries.
• No long-range radio - unbelievable radio-jamming monsters or the towns stop due to lack of benefit from the communication. If there is a benefit then towns will find a way.

Answer 4

You'll need a few components to make it work effectively, but most importantly, you'll need a series of transmitters and receivers, so that they can send and receive messages and communicate (plus some way to power the equipment, of course, which might be the hardest part). You'll likely want to use AM frequencies to get a longer reach and thus requiring less retransmission stations, depending on distance between "towns" (although this might compromise the quality of the audio, as AM signals are more irregular). Finding the necessary tools for this probably won't be too difficult, so long as there are radio stations nearby and tree monsters didn't aim to destroy them.

Now, how to make it difficult: I see 2 main ways to do it:

1- the towns are a bit too far and you can't retransmit the signals, meaning you'll have very little coverage between towns, if any at all, and the messages that do get will be hard to understand and broken up.

2-the monsters in the area utilize are rather social, and utilize very similar frequencies to communicate, resulting in lots of static and the receivers hearing either noise or a mix between the message and apparently random sounds (unless the monsters speak English) whenever the signal is being transmitted while there are monsters "talking" nearby. Which will happen and to what degree depends mostly on proximity between the monsters, the station and the receiver.

Answer 5

Using protocols like PSK31 its possible to send low speed text communications around the globe with only a few watts of transmit power and some loose wire as an antenna. The transmitter and receiver are just an ordinary cheap ham radio plus some software that could run on a $0.50 cent micro controller.

"PSK31 is distinguished from other digital modes in that it is specifically tuned to have a data rate close to typing speed, and has an extremely narrow bandwidth, allowing many conversations in the same bandwidth as a single voice channel. This narrow bandwidth makes better use of the RF energy in a very narrow space thus allowing relatively low-power equipment (5 watts) to communicate globally using the same skywave propagation used by shortwave radio stations."

https://en.wikipedia.org/wiki/PSK31

Low speed text updates are all that are needed for the government to inform the public of current events.

There are literally millions of people around the world who already own ham radios and have what they would need to talk using PSK31. The radios themselves are not large, ranging from hand held to something that sits on a workbench. A suitable antenna can be just a roll of copper wire that you threw over a tree branch.

The mechanism by which PSK31 or similar protols work is having narrow bandwidth. The only real requirement for building these kind of devices is the ability to construct very narrow band tone generators and filters that connect to AM or FM radio transceivers.

AM radio transceivers are extremely easy to build, even out of old junk electronics.