What Substation does, and where to start
Substation watches every radio channel in a band at once, and records each transmission it hears to an audio file of its own.
Plug a radio receiver into a computer's USB socket, name a band, such as the 2m amateur band, and Substation listens to the whole of it. Each time somebody transmits on one of its radio channels, Substation records what they sent, with the hiss turned down, and saves it with when it was heard, on what frequency, and how strong it was. It is made to be left running for days, and it can send each recording straight to Subsample, and each transmission to Subsequence, to play with. It runs from commands and a settings file, and needs no programming.
Where to start
- New to radio? What a software-defined radio is comes next, then Your first receiver, which helps you choose one.
- Know what a software-defined radio is already, and have a receiver? Start at Installing Substation.
- Substation installed, and working with your receiver? Start at A first scan.
A musician wanting transmissions to play with needs three chapters: Installing Substation, A first scan, and Straight into Subsample, which sends every recording Substation makes into Subsample as it is saved, with settings alone. That is the whole job. The chapters after them go deeper, to read as you need them.
What you need
- A computer running Linux, such as Debian, Ubuntu, Raspberry Pi OS or Fedora, with a USB socket. Substation is tested on Linux, as Installing Substation says.
- A terminal, the window where you type commands, and a text editor.
- To hear the air, a receiver and an antenna. Until you have them, every chapter can be followed without.
No radio knowledge and no programming are assumed. Each chapter explains what it needs where you first meet it, and nothing in this guide asks you to write code. Some chapters print a short script in a closed box, which stands in for a receiver or another app so that this site can check what Substation does: copy it as it is. Substation in your own code is for programmers alone, and nothing after it needs it.
What this guide builds
From Installing Substation on, the chapters carry one folder forward, each from where the one before it left it:
- Substation installed, its settings, and a scan of the 2m band, with a recording of a transmission it heard;
- every recording arriving in Subsample, ready to play;
- a band of your own, which Substation records;
- what Substation does between the receiver and a recording, and how it keeps transmissions and throws hiss away;
- your receiver set up for its band;
- recordings that carry when they were made, placed on an audio editor's timeline at that moment;
- an antenna's length worked out for your band;
- every transmission sent to Subsequence as well, to play from;
- and Substation running around the clock, started with the computer.
The configuration reference, the band library and the command-line reference describe every setting, band and option. This guide teaches the ones a scanner needs, and links to the rest.
Out of the box, Substation records only some bands, such as amateur and CB radio, and on the rest says when a radio channel is busy without recording it. It sets which by UK law, as its README explains under Reception and the law. Laws on receiving radio differ from country to country, so make yourself aware of the law where you are.
Test signals
Every scan this site checks is of a test signal: a recording of the 2m band as a receiver hands it to the computer, made by a short script the guide prints. So every chapter can be followed without a receiver, and this site can check what each scan prints and records. A scan with your receiver is the same command without the test signal, as A first scan shows.
How the examples are checked
Every command shown with what it printed was run, and printed what the page shows. Each time this site is built, every chapter is run twice on a fresh machine with no network, and both runs are compared with the page. Every settings example is loaded by Substation itself, and one it refuses or warns about stops the site from publishing. Every recording a scan makes is compared by what it holds: its format, its length, its sound and its details. The release they ran against is named at the foot of each page.
Some things cannot be done when this site is built: plug in a receiver, build its driver, change a setting of Linux itself, scan the air, or listen. A block that is not run says so above it, and where the point is how a recording sounds, the page says what to listen for.