Satellite

A number of Radio Amateur satellites have been launched, operated, and reached end of life. A number of them are still usable, some even multiple times a day. There new ones under development, particularly through AMSAT, The Radio Amateur Satellite Corporation (a non-profit organization), see AMSAT.org, which has groups coordinated by primarily nation representation, e.g. AMSAT-DL for Germany and a goo dportion of Europe, AMSAT-UK, AMSAT-NA, etc.

Amateur radio satellites will vary by the bands they use/make available, modes, and orbital characteristics.

Typical configurations include uplink communications (signals TO the satellite) being on separate bands from downlink communications (signals FROM the satellite). This is done to achieve isolation between the signals, as is done on earth by separating a repeater's receive and transmit frequencies.

You may envision a satellite as a repeater in the sky.

The modes a satellite operates in will vary by design and in some cases can be changed by control stations. Common modes include FM (voice), sideband (voice), and digital.

Some digital-capable satellites may operate in a "store and forward" mode instead of immediately reflecting or repeating what they "hear". A store-and-forward configuration offers the (perhaps multiple) retransmission of the data either for a number of times, at a certain time, or when the satellites approximate position reaches a certain area or range.

So far, AMSAT-originated amateur radio satellites have been active in two orbit configurations known as HEO (High Earth Orbit) and LEO (Low Earth Orbit). Generally speaking, HEO's are geo-synchronous or geo-stationary (seeming to stay in the same position with respect to an earth-based observer's viewpoint) while LEO's will have relatively rapid "passes" that will appear as if they come from different directions and at varying times. This appearance is because both of their orbital paths and earth's rotation.