This tutorial is more of an introduction about what’s possible rather than specific procedures. If you find it interesting then use your favorite search engine to look for additional information.
Handheld scanners are typically sold in electronics shops. They’re usually advertised as police-fire band or NASCAR. But they’re useful for far more than that, covering a wide variety of frequencies and can even be used to listen to signals from satellites.
A relatively simple new scanner will cost around $100. I recently picked up a used one for $5 at a yard sale. More sophisticated (read: more expensive) scanners are available, especially if you get a non-portable (benchtop) unit.
Anybody (at least in the United States) is permitted to monitor non-cellular radio frequencies. However it is illegal to inform somebody else about what you’ve heard. You do need a license if you want to transmit (e.g. aircraft, marine, amateur radio, etc.). There are many enthusiasts who just monitor radio frequencies and they overlap with amateur radio operators who also enjoy communicating with their own radios.
It’s pretty amazing that a handheld radio which is ordinarily limited to about 30-40 miles, depending on your terrain, can hear a clear signal coming from a tiny satellite in space orbiting over a hundred miles overhead. Many of the satellites aren’t much bigger than a handheld radio!
The trick is line-of-sight. With most radio signals you have to be able to “see” the transmitter (the exception is short-wave signals which bounce off of the ionosphere and other over-the-horizon phenomena). Because of the curvature of the Earth that limits you to a relatively small range unless one of the antennas is at a high location. That’s why antenna towers are as high as practical and the tops of skyscrapers and mountains are highly desirable locations for antennas.
So what’s higher than outer space?
Of course an antenna in space is also much further away from you and the square-distance law applies (a transmitter twice as far away will appear to be one quarter as powerful). But even taking that into account you can get an incredibly long range with very simple handheld equipment.
Step 1: Different types of satellites
Amateur radio satellites, including the International Space Station. It’s a thrill to listen to somebody who’s using a handheld radio half a continent away. It’s even more of a thrill to listen to an astronaut in space talking to ham radio operators on the ground and absolutely amazing if you happen to be the one talking to the astronaut. Since amateur radio satellites are designed to be relatively easy to use they’re a good start.
Spacecraft with people onboard. Many people have listened to Russia’s Mir space station, the 3 person Soyuz spacecraft, and even direct transmissions from the space shuttle.
NOAA weather satellites. Since the early 1960s weather satellites have featured APT – Automatic Picture Transmission, a simple way to receive weather satellite imagery directly from the satellite. In the 1960s this involved military surplus radios, analog circuits and a Polaroid camera pointed at an oscilloscope. Now it’s as easy as a handheld radio (or even radio on a USB stick), your computer’s soundcard, and an open source program.
Scientific satellites. A handful of scientific satellites transmit data directly to ground stations, especially when real-time response is necessary.
Military satellites. Paradoxically the fact that military satellites often transmit classified information makes them more interesting to monitor than other satellites. It’s part of the mystery that makes it more appealing. It’s relatively easy to detect the transmissions from a military satellite, but far more difficult to be able to decrypt the transmissions and actually decode the classified information. Certainly if anybody’s done the later they’ve kept very quiet about it. Just detecting the signal is an interesting challenge and even if you can’t decrypt the signal it can tell you a lot about the satellite’s orbit and its mission.
Commercial satellites. There are a variety of commercial satellites which can be monitored on a handheld scanner, most notably the ORBCOMM store-and-forward data satellites.
Technically more folks “monitor” commercial communications satellites (every time you watch cable or satellite TV) and GPS (every time you use your cell phone) but they really don’t count as DIY activities.