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Handheld scanners are typically sold in electronics shops. Theyíre usually advertised as police-fire band or NASCAR. But theyíre 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 youíve 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.
Itís 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 arenít 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. Thatís why antenna towers are as high as practical and the tops of skyscrapers and mountains are highly desirable locations for antennas.
So whatís 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
The most popular satellites to monitor for amateurs are -
Amateur radio satellites, including the International Space Station. Itís a thrill to listen to somebody whoís using a handheld radio half a continent away. Itís 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 theyíre a good start.
Spacecraft with people onboard. Many people have listened to Russiaís 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 itís as easy as a handheld radio (or even radio on a USB stick), your computerís 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. Itís part of the mystery that makes it more appealing. Itís 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 anybodyís done the later theyíve kept very quiet about it. Just detecting the signal is an interesting challenge and even if you canít decrypt the signal it can tell you a lot about the satelliteís 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 donít count as DIY activities.
Step 2: What will you hear?
In many cases satellites transmit FM voice. Itís amazing to hear a clear signal coming from outer space and realize just how far that signalís traveled to reach your radio.
Some satellites transmit fax or slow scan television (individual television frames). Theyíll sound like a fax machine.
Some satellites transmit packet data (computer data) and they generally sound like short bursts from an old dial-up modem.
The NOAA weather satellites Automatic Picture Transmission (APT) mode sounds like a fax with a distinctive plop as each line of data is transmitted.
Step 3: Factors
To listen to satellites you need to know several factors -
Hereís two excellent websites with frequencies and transmissions for a variety of satellites -
When most folks think about satellite tracking, theyíre thinking about when a satellite is visible from the ground. For a satellite to be visible itís got to be lit by the sun while the observer on the ground is in relative darkness (generally twilight). Satellites are visible for the same reason an airplane in the east is extremely bright around sunset - the planeís still lit by the sunís rays while the ground and sky around you are becoming darker.
Satellite transmitters normally donít care about sun angles so weíre interested in all of the passes of a particular satellite, not just the ones which are visible.
The http://n2yo.com/ website has real-time tracking of many different satellites, sorted by categories.
The popular Heavens-above website is primarily oriented towards visible satellite tracking but has additional features for amateur radio operators and satellite listeners. You can manually select any satellite you want to track and then click on "passes" and select "all passes."
Another choice is to run a satellite tracking program on your own computer (or smartphone). Thereís a wide variety of freeware, shareware, and commercial satellite tracking programs.
In some cases satellites are placed in orbits which will never pass over your location. The HETE-2 gamma ray burst detecting satellite was placed in a relatively low altitude orbit which hugs the Earthís equator. It could only be received by a ground station with a maximum latitude of 20 degrees. HETE-2 had a VHF transmitter which communicated with a handful of ground stations in equatorial locations to give real-time notifications whenever gamma bursts occurred around the universe. There was a commercial receiving station for a couple of thousand dollars, but in theory a hobbyist could put together a setup with a handheld scanner for a couple of hundred dollars. Plus the expenses to move to an equatorial location of course.
Determining when a satellite is in operation is often challenging.
The NOAA weather satellites transmit 24 hours a day, as long as their transmitters are working. Fortunately NOAA maintains a webpage with the status of their satellites so thatís easy to check out.
The astronauts manually operate the power switch for the amateur radio equipment on the International Space Station. Theyíre shut off a day or so before any "visiting vehicle" (cargo or people) arrives. Sometimes the crew is busy and doesnít remember to turn the amateur radio back on. During scheduled contacts with schools the astronauts will ignore anybody else trying to call them. Separate frequencies are used for the uplinks during the school contacts to minimize interference but even if you happen to come across the correct uplink frequency the astronauts will ignore you. On the other hand anybodyís within range of the school (or a relay station if one is being used) is welcome to listen in on the downlink frequency (145.800 Mhz.).
Many amateur radio satellites transmit continuously. Others have timed schedules because the satellites are dual-use satellites and performing commercial or university functions too and the amateur transmitters are only used in the spare times. In some cases power budgets only permit the transmitters to be turned on for a percentage of each orbit. In a couple of cases the batteries have failed on the satellites but fortunately failed in the open mode instead of shorting, so the satellites will continue to operate whenever theyíre in sunlight.
As a general rule Russian crewed spacecraft (Soyuz and the Russian air-to-ground and spacewalk radios on the International Space Station) are only used when theyíre over Russian ground stations. Many listeners in Europe monitor these transmissions whenever a new Soyuz launches to the International Space Station. The Russian ground network now includes three United States locations - Edwards Air Force Base California, White Sands New Mexico, and Wallops Island Virginia. These are now used only as backup sites though.
One of the more surreal experiences I had was in late 2000 as the space station was passing over the East Coast. Cosmonaut Sergei Krikalev was talking to a school on the amateur radio on 145.800 Mhz. At the same time in another module U.S. astronaut Bill Shepherd was using the Russian moduleís VHF radio on 143.625 Mhz. to talk to the Tsup (Russian mission control) via the Wallops Island relay station. The most unusual part was that Shepherd was talking in Russian while Krikalev was talking in English!
In many cases the frequencies listed for spacecraft radios are backup radios, only used in case thereís an emergency. This is especially true for NASAís major scientific spacecraft. 99.9% of the time they use microwave (S or C-Band) transmitters with highly directional antennas which point up to relay satellites stationed 22,300 miles above the equator and those signals would be next to impossible to receive from the ground. The direct spacecraft-to-ground transmitters would only be used if there is an emergency on the spacecraft.
Step 4: Better antennas
The general gag is any radio with a "rubber duckie" antenna is basically a dummy load (no antenna). Rubber duckies are designed more for durability than performance.
Itís easy to make your own antennas (anybody ever jam a coat hanger into a broken car antenna socket?). Since weíre only going to use these antennas to receive (no transmissions) theyíre extremely tolerant and you donít need any testing equipment to get a working antenna. You can optimize the performance by listening to a transmitter and making modifications (e.g. cutting a wire a little shorter) and seeing how that affects the performance.
The simplest and cheapest mod you can make for any radio with a rubber duckie (or any other whip antenna) is a "Tiger tail". All that consists of is a length of wire (19 inches is good for VHF) attached to the base of the antenna. It can be as simple as wrapping the uninsulated end of the wire around the base of the antenna. A less messy choice is to find a washer (.5 inches inside diameter is good for a BNC connector) and solder the wire to the washer. Put the washer over the radioís antenna jack and screw on the antenna. The Tiger Tail adds the missing half of the dipole antenna.
One of my favorite scanner antennas is a roll-up J-pole made from an old TV antenna cable. Remember the flat twin-lead 300 ohm antenna cables before coax cables became the defacto standard? Itís easy to make a VHF-UHF amateur radio antenna from twin lead cable (hereís just one example). Whatís especially nice for portable operations is you can roll it up and put it in your pocket.
One time I was at the VIP site for a space shuttle launch with my handheld radio and the J-pole roll up antenna. I asked a person I knew to hold the antenna for me. I told her that it was okay if the antenna got warm, but if she felt an electric shock she should drop it immediately. She almost fell for it - until I broke up laughing!
If you want a more directional antenna (which will make it possible to hear weaker signals) you can build a portable yagi. I was rather impressed by this yagi which breaks down for transport. With a portable directional antenna you point it to follow the satellite across the sky using the "armstrong" method. (Hold the handle and point it with your arm). A pass of a satellite in low earth orbit can be as long as nine minutes so I hope your armís up to the task!
Step 5: Conclusions
This is just an overview of some of the things you can do with a scanner. With a more sophisticated scanner, highly directional antennas with motorized computer controllers, and preamplifiers the skyís the limit. (Hmm, maybe sky isnít the appropriate clich to use here). Dedicated amateurs have detected the signals from the Voyager spacecraft headed out of the solar system, monitored spacecraft in orbit around Mars, and even listened in on the Apollo astronauts as they headed to the moon.
Who knows, maybe someday I will be able to hear this spacecraft!