Sheet 1 · Radio, one signal at a time
SpuriousEmissionsthe spur
A channel about radio. The signals in the air around us, the antennas and software-defined radios that hear them, and how each one works.
Move across the chart to tune. Numbered flags mark the signals an episode explains. This is an illustration of where signals sit, from 10 kHz to 2 GHz: it is not a live feed from my station, and the sounds are sketches made in your browser.
Definition
spurious emission
noun, radio engineering
- A signal that a transmitter sends by accident, right beside the one it meant to send.
- This channel. The wanted signal, and then the odd thing off to the side.
The air is full of signals that nobody sees. Aircraft and ships report where they are. Amateurs reach the other side of the world with a few watts. The sun leaves its mark on a navy transmitter.
Spurious Emissions takes one of them at a time and follows it from the antenna to the screen: what it is, what hears it, and how the message comes out.
Every tool is named and linked. A simplified picture is labelled. The mistakes stay in, because they teach the most.
Index
On this channel
The listening station
Series 01. A home station that hears aircraft, ships and shortwave, one part in each episode.
15 episodesThings to operate
The lab: interactive pages about the ideas under all of radio. They run in the browser.
6 in the labRF principles
Series 02. The ideas under all of radio, drawn as moving pictures: AM, single sideband, FM, sampling.
9 episodesSoftware-defined radio
A radio that is mostly a program. What to buy first, and what to do with it.
In preparationAmateur radio
Getting on the air. Licences, modes, and contacts across the world with a few watts.
In preparationAntennas
What goes on the roof, what goes between the antenna and the radio, and how to measure it.
In preparationWritten guides
Walkthroughs to build each part yourself: what to buy, how to connect it, what to type.
15 guidesThe parts list
Every part and every program named on the channel, with links.
41 parts
Series 01 · The listening station
From the roof to the screen
My station is a few antennas on a roof on an island in the Puget Sound, some small radios, and some small computers. It hears aircraft and ships, reads the messages that aircraft send, and receives weather maps with no internet.
- 1
A signal arrives at an antenna on my roof.
Antenna - 2
A filter removes the strong stations I do not want.
Filter - 3
A small USB radio turns the signal into numbers.
Software-defined radio - 4
A small computer reads the numbers.
Small computer - 5
A program finds the message in them.
Decoder - 6
The message becomes a dot on a map.
Screen
FIG. 2 The path of one signal. Simplified: the splitters and my home network are left out. Episode 11 shows what is really on the roof, and what I got wrong.
Series 01 · The episodes
One signal on each sheet
The series intro and episodes 1 to 3 come out on Tuesday, October 27, 2026. After that, one new episode every Tuesday, to the last one on Tuesday, December 29, 2026.
- 00Listening Station - Series IntroWhat is a listening station, and what can one hear?All of it2:19
- 01ADS-BHow do I see aircraft?1090 MHz3:09
- 02Planefence and Plane-AlertHow does it tell me about an unusual aircraft?1090 MHz6:06
- 03AISHow do I see ships?162 MHz5:29
- 04ACARS and VDL2What do aircraft say, not only where they are?131 and 136 MHz3:39
- 05ShortwaveHow does one box hear 0 to 30 MHz at once?0 to 30 MHz4:53
- 06HFDLHow do aircraft talk over oceans?2.8 to 22 MHz3:19
- 07WSPR and FT8How far does a whisper travel?14 MHz and more3:02
- 08Weather FaxHow does a ship get a weather map with no internet?518 kHz, 4 to 22 MHz3:03
- 09Distress Calls, Beacons, and HFGCSWhat else is out there? Distress calls, beacons, military voices.2 to 28 MHz4:26
- 10VLF and Solar FlaresHow does a very low frequency signal show a solar flare?near 25 kHz3:12
- 11Antennas and filtersWhat is on the roof, and what did I get wrong?The roof3:29
- 12The Station MonitorHow do I watch everything on one screen?The wall3:33
- 13Numbers StationsWho broadcasts numbers on shortwave, and what reaches my station?Coming soonShortwave, by timetable10:52
- 14RadiosondesWhat does a weather balloon feel on the way up?Coming soon400 to 406 MHz6:30
Sheet 5 · The lab
Things you can operate
Some ideas are easier to hold than to hear about. These are small machines that run in your browser. Turn the knobs until the idea is yours.
The Secret in the Sound
Every sound is a stack of pure tones. Pull one apart with your own hands, and find out how a receiver sees a whole band at once.
Open itRiding the Wave
How a voice gets onto a radio wave, and off again. Morse, AM, single sideband, FM and the digital modes, each one a thing you can play with.
Open itNumbers in the Night
A voice on shortwave reads out groups of five figures. Nobody says who it is for. What these stations are, and why the code cannot be broken.
Open itMeet Me at 455
A filter you tune gets wider as you tune up. So almost every radio keeps one sharp filter in one place and brings each station to it. Tune a crowded dial, multiply two waves, and chase the ghost station.
Open itWho Heard It First?
One plane never says where it is. Rooftop receivers hear its radio burst a few millionths of a second apart, and that is enough to find it. Start with thunder, find the curve hidden in a gap, then borrow a clock from a passing plane.
Open itSheet 6 · Gear
The parts list
41 parts and 62 programs and references, each one named in an episode and each one linked. I only list what I use.
Open the parts list| Launch | Oct 27, 2026 |
| Episodes released | 5 of 22 |
| Next out | Nov 3 · ACARS and VDL2 |
| Written guides | 15 |
| Pages in the lab | 6 |
| The long one: the whole station, end to end | planned |