AMATEUR RADIO SATELLITES
Amateur radio operators have been sending satellites into space since the early 1960’s. Now there are nearly twenty amateur radio satellites in space, and amateur radio operators can make contacts by working them. The satellites (or "birds" as they are often referred to) function like repeaters in space. Interestingly, the International Space Station also provides resources for amateur radio through the ARISS program.
These satellites are in Low Earth Orbits ("LEO") and move quickly across the sky making periods when they can be worked brief; ten minutes or less in most instances. During these periods, ham operators can use these satellites to make contact with other operators working those satellites from within its current footprint. Contacts are very brief with only call signs grid squares exchanged.
There are two types of amateur radio satellites currently in orbit:
FM Satellites - Each of these satellites uses a designated uplink frequency and a designated downlink frequency much like a cross-band repeater in space. Only one user can access and use it at a time via its specific frequencies. The strongest signal coming in keys the satellite's receiver (the Capture Effect). These are the easiest satellites to work and are often the first accessed by a beginning user.
Linear Satellites - Linear satellites work a bit like HF bands. A bandwidth of 20-60 KHz is available allowing multiple users to tune and use the bird at the same time.
An onboard transponder allows the uplink and downlink frequencies of Amateur radio satellites to utilize two different bands. An example is satellite AO-91 which uses an uplink frequency of 435.250 MHz and a downlink frequency of 145.960 MHz . Uplink transmissions usually include a CTCSS squelch tone.
You may be surprised to find that equipment you already have on hand is adequate to at least monitor these satellite repeaters as they pass over. A handheld dual-band (2M and 70CM) HT can typically be used to hear QSOs as they take place. Later, if you become more interested in this aspect of the hobby and want to actually work the birds, some additional equipment will be necessary. But you will be operating at low power (5 watts is adequate) so a full duplex dual-band HT (or two HTs), a handheld dual-band yagi with a duplexer, and satellite software or smart phone app will get you into satellites at the entry level.
The software or app (detailing when such satellites will pass overhead and other related information) are available online. Both computer software programs and smart phone applications are available. For iPhone users, the GoSatWatch app is often utilized.