Radio and communication technologies are recurring topics. Here are a few quick start notes.
Precursor: This article was edited slightly in wording and order of paragraphs, but is overall the same document. You can find the original page here
Both /cyb/ general and /ham/ general on 4chan’s /g/ + /diy/ boards respectively relate to radio communications and technology. The idea is to have this FAQ to answer all the immediate questions. It is bootstrapped off the Cyberpunk FAQ and the 4chan radio pasta. This is Version 1 preview 10 of the Radio FAQ. Presently the maintainer follows alt.cyberpunk hierarchy (which is easily done) and /cyb/ and /ham/ when operative. This FAQ and later versions will be on FTP.
I would also like to recognise and express my fellow anons. This FAQ is a living document. If you have any comments, criticisms, additions, questions please post them in a /sec/ general. (I especially welcome reports of “broken links”, either in the ASCII or HTML versions). The vast number of the “answers” here could be predicated by “in several peoples opinion.” The general consensus is however that no one person is the ultimate authority.
Yes, radio communication can get you around the Earth. Literally. You can do that in many ways.
VLF, LF: these band can go through the Earth and are used for reaching submarines. There is a radio amateur band available at 2200 m but to transmit here you’d better use a manly antenna - 600 m length on your own pylons would do.
HF: the workhorse long distance band with several radio amateur bands where you with some skill can transmit around the globe at 10 W
VHF and up: there are many bands available with specific services:
A: you can use the radio amateur packet radio system using store and forward and send data across the world
B: you can use radio amateur satellites (see OSCAR)
C: you can use meteor scatter
D: with care you can use moon bounce or EME to reflect signal back to Earth
(B, C and D will give intercontinental range but not necessarily full globe coverage)
Get a license. Seriously. There are many good reasons for this. To get a license you have to learn a few important things:
This is important for many reasons such as making sure you don’t kill yourself or jam emergency bands with harmonics. Remember that at resonance you can generate very high voltages and 100 W power are common and should be taken seriously. Your editor was fried on 100 W HF currents once. On the other hand a valid license you are allowed to make you own equipment, explore new designs involving high voltage gear that would incinerate an elephant.
This is important to make sure you can coexist on the band with others. In case of emergencies knowing protocols is essential. Part of this is knowledge of Q-code and Z-code for commonly used abbreviations.
This lets you know what frequencies will work well under what circumstances, and there are many bands, many with important limitations. As a licenced ham you can use the 136 kHz (2200 m) band on LF, up to > 300 GHz (sub mm) band on THF. Also important is to know what types of transmissions are permitted at the different bands. Bandplans are put in place to assist in coexistence on the radio waves. Reasoning might not be apparent at first glance but there are reasons behind it all.
If you really, really, really need to transmit without being found there are a lot of things to know. This is one of the reasons it takes time to train military radio operators.
With a license you get a call sign. Without a valid call sign you will stick out like a sore thumb. Just think of teenage script kiddies who have just downloaded LOIC and is boasting on a computer security forum.
Hams are used in emergencies when the message absolutely has to get through and cell phone nets are down and normal infrastructure such as mains power and landlines have failed. Normal activities are far less dramatic. Rather it is tech and social.
- chat with people all over the world
- collect QSL cards
- long distance work (DX)
- master high speed Morse (can be pretty impressive!) and win competitions.
All kinds of people are active. While the stereotype is an elderly man in questionable health, the very young are also active. Many people who are disabled use ham to stay in contact with the world. Also, many are former telegraphists from the merchant navy or the armed forces.
- make you own equipment, explore new designs (with a license you are allowed to make high voltage gear that would incinerate an elephant)
- antenna design - you would be surprised how much effort can be put into this
- new communication forms, especially digital modes with fancy modulation
- explore MIMO, beam forming etc.
- new ways of direction finding (DF)
- explore Digital Signal Processing (DSP) algorithms for radio
- see how far you can communicate with as little emitted power as possible (also impressive results)
- locate noise source
Modern electronics has made Software Defined Radios (SDR) cheap (20 USD) and available for everyone and essentially replaces a lot of analogue electronics with Digital Signal Processing (DSP) on a computer such as a PC or even a Raspberry Pi.
With today’s technologies many wonder why use primitive Morse code. Part of the reason is exactly that it is primitive: it is simple in terms of electronics, it is relatively simple to operate and you can keep long distance communications going under adverse conditions including burning through military jammers. A transceiver with key can be as small as a deck of cards and that includes the battery. Bandwidth use is very small. For these and other reasons WWII agents behind enemy lines often used Morse code to keep in touch with HQ. A properly trained military Morse code operator will know how to transmit to the target without being caught by enemy intelligence. Today the practical use is that you can bring your radio with you everywhere.
Wikipedia has an article on Morse code.
Not all activities require a license. In most free countries you do not need a license for reception only with a few exceptions. Listening in to cell phone traffic is typically not permitted. Also listening in on police radio is also frowned at in some countries though these days much of this is encrypted.
It is the use of transmitters (or intentional radiators) that usually requires permission or a license, especially if you made the transmitter yourself. One example is the use of ISM bands. These bands were for Industrial, Scientific and Medical equipment, essentially machines that had to emit at least some radio frequency (RF) noise, and by setting a few bands aside from this the rest of the bands would be free from junk. The 2.4 GHz band is one example, used by microwave ovens but also modern tech such as WIFI, Bluetooth, Zigbee and other protocols. The permission for use comes with the equipment. It is not entirely clear if these bands are free for use with experimenters even though emitted power is kept low.
You can get cheap transceivers operating on a single band, Morse only, for about 50 dollars. For a few hundred dollars more you can get Elecraft transceivers, some of which are very portable. QRP transceivers are cheap and cheerful and often easily adaptable for further experiments. A lot of Chinese vendors such as Frog Sound QRP sell single band (typically around 7.020 MHz) Morse code transceivers for a few dollars. The S-Pixie QRP design is popular and costs about 4 USD as a kit from many vendors in China, including an acrylic case. There are two important snags. First of all the frequency is set to 7.023 MHz which in the US requires an Extra class license. That can be fixed by replacing the crystal with one within the 40 m band. The other issue is that the Pixie emits a lot of harmonics, often quite a bit above the permissible.
At VHF and UHF you can get cheap Baofeng radios.
If you want to try a receive only, you do not require a license. A cheap Software Defined Radio (SDR) like RTL-SDR is good bang for the bucks and gives you huge coverage. SDR is very popular and even has dedicated news sites.
A chain is only as strong as its weakest link and no radio system is better than the antenna. A good enough antenna is not hard to make and does not require a license though neighbour and home owner associations can complain. Stealth antennas are therefore also a thing.
With a cheap copper or bronze wire, you can make a good antenna:
|Distance between poles (m)||Wire Length (m)||Solid centre conductor wire diameter (bronze) (mm)||Solid centre conductor wire diameter (copper) (mm)||Multi-stranded wire (bronze) (mm)||Multi-stranded wire (copper) (mm)|
|25||26||1||1.6||0.35 x 7||0.5 x 7|
|40||41||1.5||2.1||0.5 x 7||0.67 x 7|
|50||52||2.1||2.6||0.67 x 7||0.52 x 19|
|60||62||2.1||3||0.67 x 7||1.0 x 7|
|70||72||2.6||3||0.67 x 7||1.0 x 7|
|80||82||2.6||3.2||0.52 x 19||0.67 x 19|
Making receivers is possible without making transmission and the simplest way to start is to make crystal receivers. Simple in principle the receivers can be made in pretty complicated versions, all powered by the received radio waves without need for an internal power source. There are guides for making these freely available on the net.
Reception and Decoding
When you listen through the bands you will come across a lot of activities that are not immediately obvious what are. In the old days you have voice and Morse, then Radio Teletype (RTTY) and these days we have a lot of different modulation schemes for various purposes. Signal Intelligence (SIGINT) was once the sole prerogative of governments but these days anyone can analyse and decode. A lot can be found on the aptly named Signal Identification Wiki.
As an alternative to listening using your own radio you can listen in using web connected SDR services. One of the first was WebSDR which is a portal to more than 100 SDR servers across the world, selectable through a list or a map. Another alternative is the open source OpenWebRX for KiwiSDR which is also a remote radio listening system, with a list of receivers. There are also other alternatives with propagation data.
It is also possible to use ham equipment to listen to astronomical phenomena and you can even order kits for participating.
There is a lot of cold war rules to this activity, all bands are monitored and emitters located as a matter of routine with ground and space based SIGINT systems. Even accidental transmissions into military emergency bands will bring about swift reactions.
Below 30 MHz you will be caught by systems like the Wullenweber, huge antenna systems that at 300 m diameter have earned the nickname “Elephant cages”. These are used for direction finding (DF) and have enormous ranges. Some are capable of determining distance in addition to direction and can perform single site localisation. Otherwise direction finders work in groups to locate emitters by intersection of vectors.
And make no mistake, you will be found. And recorded, voice prints archived for future use.
These days the availability of high tech equipment has meant that also hobbyists can do what only government agencies could do 20 years ago. The KiwiSDR radio is provided with a GPS receiver that enables locating emitters using Time Difference of Arrival (TDOA). Since a large selection of such radios are on the net these can be connected from anywhere in the world to locate emitters without the need for your own radio.
Wideband recording are made of all amateur radio bands during contests and the automated conversion to text of QSOs during contests as a way to enforce the rules. These are logged and kept. Since logging the entire HF band generates perhaps 60 MB/s it is quite easy for a dedicated amateur to keep raw data for later analysis. Logging amateur bands only reduces bandwith requirements even further.
Also services like Broadcastify keep rolling 1 month recordings of all scanners that people have linked to it. That includes public safety, aircraft, rail, and marine radio live audio streams.
More information can be found on Amateur Radio Wiki - The Online Encyclopedia for Hams (Does anyone have an updated link to this wiki? The current active one is a spam site).