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Subelement T8
Modulation modes: amateur satellite operation; operating activities; non-voice and digital communications
Section T8B
Amateur satellite operation; Doppler shift; basic orbits; operating protocols; transmitter power considerations; telemetry and telecommand; satellite tracking
What telemetry information is typically transmitted by satellite beacons?
  • The signal strength of received signals
  • Time of day accurate to plus or minus 1/10 second
  • Health and status of the satellite
  • All of these choices are correct

Health and status of the satellite is telemetry information typically transmitted by satellite beacons.

Some satellites may transmit other information, but the key word here is typical.

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Tags: arrl chapter 6 arrl module 16

What is the impact of using too much effective radiated power on a satellite uplink?
  • Possibility of commanding the satellite to an improper mode
  • Blocking access by other users
  • Overloading the satellite batteries
  • Possibility of rebooting the satellite control computer

Most analog satellites have what are called linear transponders which retransmit signals in a relatively large "band" often 50-100kHz wide (the passband). What this means, in effect, is that multiple simultaneous signals can be retransmitted (repeated) at the same time.

The trouble is, if one of the signals is significantly more powerful than the other signals it can effectively "blank out" the other signals -- somewhat like how you might be able to see three separate dim flashlights on a distant hill, but if one of them is a powerful flood light you would likely be blinded by that light and unable to see the other two dimmer lights.

Thus, you should never use more power than you need when using a repeater because doing so may "blind" the linear transponder to the other signals and block access by other users.

For more information, see the ARRL's An Amateur Satellite Primer

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Which of the following are provided by satellite tracking programs?
  • Maps showing the real-time position of the satellite track over the earth
  • The time, azimuth, and elevation of the start, maximum altitude, and end of a pass
  • The apparent frequency of the satellite transmission, including effects of Doppler shift
  • All of these choices are correct

Satellite tracking programs tell you where a satellite is at a given time, including its altitude and where it will be at the start and end of a pass, relative to your location.

The tracking programs even tell you how much to change your transmitter's and receiver's frequency to compensate for the Doppler shift you get when the satellite is coming toward you or moving away from you.

So all of these answers are correct.

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What mode of transmission is commonly used by amateur radio satellites?
  • SSB
  • FM
  • CW/data
  • All of these choices are correct

Some of the things that you can get from the CW beacon is the mode the satellite will be in at which phase counts, keplerian data and other general announcements. The RTTY bulletins contain the same data as the CW plus satellite status telemetry. Packet (AX.25) is also used for telemetry. (http://www.amsat.org/articles/houston-net/beacons.html)

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What is a satellite beacon?
  • The primary transmit antenna on the satellite
  • An indicator light that shows where to point your antenna
  • A reflective surface on the satellite
  • A transmission from a satellite that contains status information

A beacon provides us with a gauge to determine how much power we should use. If you transmit your signal and compare it to the beacon strength, you can then adjust your power up or down to match the beacon. That would be the optimum transmitting power for your station. The next thing that the beacons provide us with is a schedule of the satellite's activity. It might tell you that it is on during a particular time period and off during others.

The beacon can also help us tune our radio to compensate for doppler shift. Since we know the beacon is supposed to be on a certain frequency, we can calculate where our signal will be based on the current reception of the beacon (http://www.amsat.org/articles/houston-net/beacons.html)

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Which of the following are inputs to a satellite tracking program?
  • The weight of the satellite
  • The Keplerian elements
  • The last observed time of zero Doppler shift
  • All of these choices are correct

Keplerian elements are the parameters that define the orbit of a satellite. From these elements, the program can compute the time and bearing of a satellite pass, relative to your position on the earth.

The weight of the satellite enters into the equation, but it's the Keplerian data that the tracking program uses.

The last observed time of zero Doppler shift would be the time that the satellite was moving neither toward you nor away from you (like when it was overhead, for example). While this might be interesting data, it isn't enough to predict where it will be coming from or going to on its next pass, or at what altitudes.

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With regard to satellite communications, what is Doppler shift?
  • A change in the satellite orbit
  • A mode where the satellite receives signals on one band and transmits on another
  • An observed change in signal frequency caused by relative motion between the satellite and the earth station
  • A special digital communications mode for some satellites

The most common references to the doppler effect (or doppler shift) refer to sound; one of the most common examples used in highschool science classes involves a fire engine (or other vehicle with a siren) whose siren seems to drop in pitch drastically when the vehicle passes you. The producer of the sound does not actually change frequency, but the relative speed of the vehicle producing the sound to the object (you) receiving the sound makes it seem to you that it does.

The same principle applies to a radio frequency signal; the relative motion between a satellite and the earth station can cause a shift in the frequency at which you can receive the signal depending on what its position and momentum are relative to the receiving station.

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Tags: satellite operation frequencies arrl chapter 6 arrl module 16

What is meant by the statement that a satellite is operating in mode U/V?
  • The satellite uplink is in the 15 meter band and the downlink is in the 10 meter band
  • The satellite uplink is in the 70 centimeter band and the downlink is in the 2 meter band
  • The satellite operates using ultraviolet frequencies
  • The satellite frequencies are usually variable

"mode U/V" is short for "mode UHF/VHF" -- meaning that the uplink is UHF, meaning 70 cm, and the downlink is VHF, meaning 2 meters. There are of course other UHF bands besides 70cm and other VHF bands besides 2m, but they are not commonly used by amateur radio operators and so the term is understood to mean the standard UHF/VHF bands.

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What causes spin fading of satellite signals?
  • Circular polarized noise interference radiated from the sun
  • Rotation of the satellite and its antennas
  • Doppler shift of the received signal
  • Interfering signals within the satellite uplink band

Satellites are not stationary in space; they are constantly moving, and generally they are rotating as well. As they turn, the antennas on the satellite change position relative to your location. The signal may fade if the antennas are directional, or even if omnidirectional, if they are obscured by the rest of the satellite.

This is referred to as "spin fading" because the fading is caused by the satellite spinning around.

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What do the initials LEO tell you about an amateur satellite?
  • The satellite battery is in Low Energy Operation mode
  • The satellite is performing a Lunar Ejection Orbit maneuver
  • The satellite is in a Low Earth Orbit
  • The satellite uses Light Emitting Optics

Just remember that we are talking about a satellite; this question could be a bit tricky if you haven't seen it before, but LEO refers to the position, not to any operation. It is, as the answer indicates, Low Earth Orbit.

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Who may receive telemetry from a space station?
  • Anyone who can receive the telemetry signal
  • A licensed radio amateur with a transmitter equipped for interrogating the satellite
  • A licensed radio amateur who has been certified by the protocol developer
  • A licensed radio amateur who has registered for an access code from AMSAT

Yep, anyone who can receive the telemetry signal is allowed to receive telemetry from a space station but not allowed to transmit to one without a license.

With the availability of inexpensive RTL-SDR USB dongles, many people are trying their hand at receiving telemetry from space stations even if they don't have a license. For some of us, this sort of thing is what got us interested in amateur radio to begin with.

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Which of the following is a good way to judge whether your uplink power is neither too low nor too high?
  • Check your signal strength report in the telemetry data
  • Listen for distortion on your downlink signal
  • Your signal strength on the downlink should be about the same as the beacon
  • All of these choices are correct ~

The term uplink suggests that the question was written with amateur radio satellites in mind; most amateur radio satellites have what is called a linear transponder, which listens to a relatively large passband (perhaps 50-100kHz wide, where a normal SSB signal uses 3kHz or less) and retransmits it on another frequency (the downlink). In this way, multiple signals can be carried simultaneously by the satellite.

If your uplink power is too low, your signal coming back may not be strong enough to be heard; on the other hand, if your power is too high you could "blind" the satellite to other signals, blocking them from using it.

The satellite will constantly transmit a morse code (CW) beacon on the downlink; you can use that and compare it to your signal strength when it comes down. If your signal is stronger than the beacon then you are likely overloading the receiver and potentially blocking other users; if your signal is weaker than the beacon then the receiver isn't hearing you as strongly as it could. Adjust your power until the your signal strength on the downlink is the same as the beacon and you're in the "just right" zone =)

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