Friday, May 30, 2014

Operating via Ham Radio Satellites

Non-ham radio operators are usually pretty surprised when you tell them about ham radio satellites. The first amateur radio satellite, OSCAR-1 (which stood for Orbiting Satellite Carrying Amateur Radio), was built by American hams and went into orbit in 1961, just a couple of years after the Russians launched the Sputnik satellite, igniting the space race. Today, hams have quite a number of satellites with missions ranging from digital mailboxes to repeaters to scientific experiments.

Satellite basics

Most amateur radio satellites are located in near-circular Low Earth Orbit, or LEO, circling the earth a number of times each day. A few have non-circular “Molniya” orbits that take them high above the earth where they are visible for hours at a time. (Molniya is “lightning” in Russian and is the name given to their fleet of communications satellites that travel in elliptical orbits.) For practical and regulatory reasons, satellite transmissions are restricted to the bands on 10-meters; on the 2-meter, 70-cm; and microwave bands at 1296 MHz and higher. The ionosphere usually does not pass signals at lower frequencies and satellite antennas need to be small, requiring shorter wavelength.

The input frequencies are called the uplink and the output frequencies are
called the downlink. The numbers that describe a satellite’s orbit (and allow
software to determine where it is) are called the orbital or Keplerian elements.
These pieces of information allow you to operate using a satellite!
You find three common types of satellites.

Transponder: These satellites listen on a range of frequencies on one
band, translate those signals to a different band, and then retransmit
them in real time.

Repeater: These satellites act just like terrestrial repeaters, listening and
receiving on a specific pair of channels. Satellite repeaters are crossband,
meaning their input and output frequencies are on different bands.

Digital: Digital satellites can act as bulletin boards (BBS) or as store-and forwardsystems. You can access both types of digital satellites using regular packet radio protocols and equipment. The International Space Station (ISS) and Space Shuttle (STS)  both have digital BBS systems available to hams on the ground. The ISS also has an APRS digipeater onboard! Store-and-forward satellites act as message gateways, accepting messages and downloading them to a few control stations around the world. The control stations also pass messages back up to the satellites that are downloaded by ground-based
users. Digital satellites are very useful to hams at sea or in remote locations.

Accessing the satellites

The best place to go to find out which satellites are active and in what mode
is the AMSAT home page ( Click the Satellite Frequencies
and Status link to get the complete set of information on what each satellite
does and its current operational status.

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