WEBVTT NOTE Amateur Satellites 1 00:00:00.000 --> 00:00:10.138 Why this is a Technician topic. Satellite work sits entirely in the VHF and UHF bands, where a Technician holds full privileges. 2 00:00:10.138 --> 00:00:25.425 A handheld with a small directional antenna genuinely works satellites, this is one of the few places where the entry-level licence gets the whole experience with no restriction at all. Orbits. 3 00:00:25.425 --> 00:00:32.745 Question. What does the term LEO mean in reference to communication satellites? 4 00:00:33.645 --> 00:00:40.325 Answer. Low Earth Orbit, which has a period of around 100 minutes. 5 00:00:40.925 --> 00:01:00.632 Roughly a hundred minutes per orbit means a pass over your location lasts about ten to fifteen minutes, and the satellite is moving fast enough that everything below follows from it: you must track it, and its frequency shifts while you do. 6 00:01:00.632 --> 00:01:08.925 Mode designations. Satellites name their bands with a two-letter code: uplink first, downlink second. 7 00:01:08.925 --> 00:01:16.605 Question. What does it mean if a satellite is operating in U/V mode? 8 00:01:17.505 --> 00:01:25.505 Answer. The satellite uplink is in the 70-centimeter band and the downlink is in the 2-meter band. 9 00:01:26.105 --> 00:01:41.457 The letters: U is 70 cm (UHF), V is 2 m (VHF), L is 23 cm, S is 13 cm. So U/V means transmit on 70 cm, listen on 2 m; V/U is the reverse. 10 00:01:41.457 --> 00:01:58.714 Uplink and downlink are on different bands so that the satellite can receive while transmitting, the same reason a repeater uses an offset, taken further. 11 00:01:58.714 --> 00:02:14.627 Amateur satellites use all the common transmission modes, the pool answers "all these choices are correct" for FM, SSB, and CW. Doppler shift. 12 00:02:14.627 --> 00:02:20.587 Question. What is Doppler shift in reference to satellite communications? 13 00:02:21.487 --> 00:02:30.112 Answer. An observed change in signal frequency caused by relative motion between the satellite and Earth station. 14 00:02:30.712 --> 00:02:44.317 A satellite approaching you compresses the wave, the received frequency reads high. Departing, it reads low. The shift passes through zero at closest approach. 15 00:02:44.317 --> 00:02:58.264 The magnitude scales with frequency: a few kilohertz on 70 cm, a fraction of that on 2 m. In practice you continuously retune during a pass, or let software do it. 16 00:02:58.264 --> 00:03:13.152 This is why an SSB satellite contact requires an active hand on the dial, and why FM satellites are more forgiving, an FM receiver tolerates a few kHz of offset. Spin fading. 17 00:03:13.152 --> 00:03:18.352 Question. What causes spin fading of satellite signals? 18 00:03:19.252 --> 00:03:24.212 Answer. Rotation of the satellite and its antennas. 19 00:03:24.812 --> 00:03:39.738 Many satellites spin for stabilisation, which sweeps their antenna pattern and polarisation past you. The result is a periodic rise and fall of signal, at the spin rate. 20 00:03:39.738 --> 00:03:47.863 It is a characteristic of the satellite, not a fault in your station. Beacons and telemetry. 21 00:03:47.863 --> 00:03:51.438 Question. What is a satellite beacon? 22 00:03:52.338 --> 00:03:58.421 Answer. A transmission from a satellite that contains status information. 23 00:03:59.021 --> 00:04:05.621 Question. What telemetry information is typically transmitted by satellite beacons? 24 00:04:06.521 --> 00:04:10.681 Answer. Health and status of the satellite. 25 00:04:11.281 --> 00:04:15.142 And a rule worth knowing because it is unusual: 26 00:04:15.142 --> 00:04:21.622 Question. Who is permitted to receive telemetry from an amateur radio satellite? 27 00:04:22.522 --> 00:04:25.162 Answer. Anyone. 28 00:04:25.762 --> 00:04:42.571 No licence needed to receive it, and no restriction on decoding or sharing it. Amateur satellite telemetry is deliberately open, and networks of unlicensed listeners routinely contribute to satellite health monitoring. 29 00:04:42.571 --> 00:04:50.204 Setting uplink power. This is the etiquette question that matters most, and the pool asks it twice. 30 00:04:50.204 --> 00:04:58.604 Question. What is the impact of using excessive effective radiated power on a satellite uplink? 31 00:04:59.504 --> 00:05:03.883 Answer. Blocking access by other users. 32 00:05:04.483 --> 00:05:18.759 A linear transponder shares its limited output power among every signal it hears. One station running far too much power takes most of that output and everyone else drops out. 33 00:05:18.759 --> 00:05:27.243 It is not merely rude; it denies the satellite to everybody in the footprint. The self-check is elegant: 34 00:05:27.243 --> 00:05:39.523 Question. Which of the following is a way to determine whether your satellite uplink power into a linear transponder satellite is neither too low nor too high? 35 00:05:40.423 --> 00:05:47.303 Answer. Your signal strength on the downlink should be about the same as the beacon. 36 00:05:47.903 --> 00:06:06.703 Listen to your own downlink and compare it with the satellite's beacon. Louder than the beacon means back off. Much quieter means you may add a little. It costs nothing and it is entirely self-administered. Tracking. 37 00:06:06.703 --> 00:06:12.934 Question. Which of the following are inputs to a satellite tracking program? 38 00:06:13.834 --> 00:06:17.634 Answer. The Keplerian elements. 39 00:06:18.234 --> 00:06:29.314 A compact set of orbital parameters, published and updated regularly, from which a program computes where the satellite is at any moment. 40 00:06:29.314 --> 00:06:42.243 Question. Which of the following are provided by satellite tracking programs? A. Maps showing the real-time position of the satellite track over Earth. B. 41 00:06:42.243 --> 00:06:59.874 The time, azimuth, and elevation of the start, maximum altitude, and end of a pass. C. The apparent frequency of the satellite transmission, including effects of Doppler shift. D. All these choices are correct. 42 00:07:00.774 --> 00:07:04.294 Answer. All these choices are correct. 43 00:07:04.894 --> 00:07:22.664 Azimuth and elevation tell you where to point. Rise and set times tell you when to be there. Maximum elevation tells you whether a pass is worth the effort, a pass topping out at ten degrees is scraping the horizon. 44 00:07:22.664 --> 00:07:36.466 Check yourself. A satellite is in V/U mode. Which band do you transmit on? Your downlink signal is noticeably stronger than the satellite's beacon. What should you do? 45 00:07:36.466 --> 00:07:43.905 Your received signal rises and falls smoothly a few times during a pass. Fault or feature? 46 00:07:49.905 --> 00:08:05.421 2 metres, uplink is named first, and V is 2 m. Reduce power. Excessive uplink ERP takes transponder output from everyone else. Match the beacon. 47 00:08:05.421 --> 00:08:13.825 Neither, it is spin fading, caused by the satellite and its antennas rotating.