How the Telstar Satellite Works
A lot of facts and figures sometimes lead only to confusion, but these pages may help make things clearer. Here you can see—step by step—exactly what happens during a typical pass of the Telstar satellite over the Andover ground station:
1 The satellite comes over the horizon.
2 The command tracker, knowing from computer data the satellite’s approximate location, begins to search for its continuous 136-megacycle beacon. A quad-helix antenna (four long spirals) tracks the satellite to an accuracy of one degree.
3 When the satellite is located, the command transmitter turns on the satellite’s transistor circuits and telemetry. The ground station then checks on the satellite’s operating condition, as reported by telemetry.
4 The command transmitter then turns on the satellite’s traveling-wave tube, which starts the transmission of a 4080-megacycle beacon signal.
5 The precision tracker—an eight-foot parabolic dish (known as a Cassegrainian antenna) mounted on a pylon—locates this beacon and tracks it to within one-fiftieth of a degree.
6 The horn antenna’s autotrack mechanism, which is pointed by both the precision tracker and data from magnetic tapes, locates the satellite’s beacon signal.
7 Now the horn antenna locks onto the satellite, with the autotrack continuing to make fine adjustments in pointing the horn.
8 The equipment is now ready for communications signals to be sent from the two-kilowatt ground transmitter to the satellite.
9 The satellite receives the signals and converts them down to a frequency of 90 megacycles; they are amplified in transistor circuits and converted up to a new frequency of 4170 megacycles.
10 The signals are amplified again by the traveling-wave tube—for a total amplification of as much as ten billion times—to get a radiated power of 2¼ watts.
11 The 4170-megacycle signals are now transmitted in all directions by the satellite’s equatorial antenna.
12 These signals can be picked up at Andover or at any other ground station equipped with a suitable antenna that is within line of sight of the satellite.
13 At Andover, the received signals are amplified by means of a solid-state maser and a frequency-modulation-with-feedback circuit.
14 They can now be relayed via regular land lines to their destination.
15 Near the end of a pass, the command tracker turns off the communications circuits and telemetry in the satellite.
16 The satellite drops below the horizon.