It is a common perception that it requires sophisticated equipment and large circularly polarised antenna arrays to work amateur satellites. While this may be true for using some of the high altitude ‘birds’ or on the higher bands such as 23cm, it isn’t the case for all satellites. There are several low Earth orbiting satellites which can be worked with relatively simple transceivers and antennas. This article will concentrate on voice operation, as I have no experience at all with digital satellite operation.
Amateur voice satellites can be divided broadly into two groups. Firstly, there are the traditional “linear transponder” satellites. These satellites receive a specific range of frequencies (typically 40 – 100 kHz) in one band, convert them to another band using a mixing process similar to that used in a superheterodyne receiver and amplify the converted signal for transmission back to Earth. Linear transponders are capable of relaying several different signals simultaneously. More recently, some satellites have been carrying crossband FM repeaters instead of linear transponders. These repeaters are similar to their familiar terrestrial cousins in that they receive an FM signal on a specific channel, demodulate the signal and retransmit the signal on a new frequency. Unlike linear transponders, but like conventional FM repeaters, these satellites can only carry one QSO at a time. Most amateur voice satellites use linear transponders.
To successfully work an amateur satellite, you need to have transceivers suitable for the satellites you wish to work. For linear transponders, SSB and CW transceivers on the bands of interest are required. For the FM repeaters, either a dual band FM transceiver with crossband transmit/receive capabilities or separate 2m and 70cm FM transceivers are suitable. A related issue is which bands to use. FM users don’t have much choice. All of the FM satellites (operational or proposed) use 2m and 70cm, with one of these bands being used for the uplink, the other for the downlink. There are a wider variety of frequencies in use by linear transponder satellites.
For antennas, an existing HF dipole and VHF/UHF omnidirectional antennas will work in a pinch. The typical VHF/UHF collinears typically have a low angle of radiation, and better results may be obtained with a simple ¼ wave groundplane, or for the more serious, a turnstile antenna. If you have crossed Yagis and AZ/EL rotators, all the better (but then this article isn’t aimed at you in this case! :-). Finally, though not essential, it is very strongly recommended to have a computer, satellite tracking software and an Internet connection available. The Internet connection is for downloading the latest Keplerian elements for the tracking software (and the software itself if you don’t have any), as well as checking satellite home pages for transponder schedules and other information. Besides, the Internet is fun when the birds aren’t overhead!
Working your first satellite! This isn’t anywhere near as daunting as it sounds. The first thing is to have a look around your shack and see what equipment you have. If, like many amateurs, you have FM only radios on VHF/UHF, then you are limited to the FM satellites. Those lucky ones with all mode transceivers can also try their hand at the linear transponders. If SSB or CW satellite operation interests you, it’s a natural progression to move on from FM. For those interested in exploring SSB/CW operation via linear transponders on satellites, there is are several excellent introductory articles on AMSAT’s web site.