This group covers how amateur satellites work, how to predict their passes, what you hear from them, and how to use them without causing problems for others.
Orbits and passes
Most amateur satellites are in Low Earth Orbit (LEO), with an orbital period of around 100 minutes. Each one is above your horizon for only a short time, called a pass, so you need to know when and where to point your antenna.
Tracking programs
A satellite tracking program shows:
A map of the satellite’s real-time position and ground track.
The time, azimuth and elevation for the start, maximum elevation and end of each pass.
The apparent frequency of the satellite’s signal, corrected for Doppler shift.
Its inputs are the Keplerian elements, a set of numbers describing the orbit. These must be kept up to date to give accurate predictions. Transmitted power is not an input.
Doppler shift
Doppler shift is an apparent change in frequency caused by relative motion between the satellite and your station. The signal sounds higher while the satellite approaches and lower as it moves away, so you may need to retune during a pass. It does not change the orbit or reflect a change in the satellite itself.
Spin fading
Satellites that rotate present changing antenna orientation and polarization toward you. The signal rises and falls in a regular pattern. This effect, caused by rotation of the satellite and its antennas, is called spin fading.
Modes and band names
Amateur satellites use several modes: SSB through linear transponders, FM like a repeater in space, and CW or data for beacons and digital payloads.
Mode letters name bands, uplink first and downlink second. U/V mode means the uplink is UHF (70 cm) and the downlink is VHF (2 meters). V/U would be the reverse.
Beacons and telemetry
A satellite beacon is a transmission containing status information about the satellite, such as battery voltage and temperatures. This telemetry reports the health and status of the satellite, not your signal strength or exact time. It also helps you find and identify the satellite. Telemetry is not encrypted, and anyone may receive it.
Using a linear transponder
A linear transponder retransmits a whole segment of spectrum. If you use too much effective radiated power on the uplink, you can capture the transponder and block access by other users. A good check is to listen to the downlink: your signal should be about as strong as the satellite’s beacon. If it is stronger, reduce power. Distortion, telemetry signal reports and internet SDRs are not the standard test.
Key facts to memorize
LEO means Low Earth Orbit, with a period of around 100 minutes.
Keplerian elements are the input a tracking program needs.
Doppler shift is a frequency change caused by relative motion.
U/V mode: uplink 70 cm, downlink 2 meters.
Spin fading is caused by rotation of the satellite and its antennas.
Beacons transmit satellite health and status telemetry.
Anyone may receive satellite telemetry.
Too much uplink power blocks other users.
Downlink strength should match the beacon’s.
Memory hooks
Mode letters read “uplink / downlink”: U/V is up on UHF, down on VHF.
Questions in this group (12): answers shown
T8B01
What telemetry information is typically transmitted by satellite beacons?
A. The signal strength of received signals
B. Time of day accurate to plus or minus 1/10 second
C. Health and status of the satellite ✓ Correct answer
D. All these choices are correct
Satellite beacons transmit telemetry about the satellite's own health and status, such as battery voltage and temperatures. They do not report your received signal strength or provide precise time of day, so the other choices do not fit.
T8B02
What is the impact of using excessive effective radiated power on a satellite uplink?
A. Possibility of commanding the satellite to an improper mode
B. Blocking access by other users ✓ Correct answer
C. Overloading the satellite batteries
D. Possibility of rebooting the satellite control computer
On a satellite uplink, too much effective radiated power drives the transponder harder, which can capture its receiver and block access by other users. It does not command a mode change, drain the batteries or reboot the computer.
T8B03
Which of the following are provided by satellite tracking programs?
A. Maps showing the real-time position of the satellite track over Earth
B. 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 ✓ Correct answer
Tracking programs show a real-time map of the ground track, list the start, maximum elevation and end times with azimuth and elevation for each pass, and display Doppler-corrected frequencies. All three are standard features.
T8B04
What mode of transmission is commonly used by amateur radio satellites?
A. SSB
B. FM
C. CW/data
D. All these choices are correct ✓ Correct answer
Amateur satellites use SSB through linear transponders, FM through repeater-style satellites, and CW or data for beacons and digital payloads. Since every listed mode is in use, all of the choices are correct.
T8B05
What is a satellite beacon?
A. The primary transmit antenna on the satellite
B. An indicator light that shows where to point your antenna
C. A reflective surface on the satellite
D. A transmission from a satellite that contains status information ✓ Correct answer
A satellite beacon is a transmission from the satellite carrying status information, such as telemetry, and it helps you find and identify the satellite. It is not an antenna, an indicator light or a reflector.
T8B06
Which of the following are inputs to a satellite tracking program?
A. The satellite transmitted power
B. The Keplerian elements ✓ Correct answer
C. The last observed time of zero Doppler shift
D. All these choices are correct
A tracking program needs Keplerian elements, the orbital parameters (epoch, inclination, period and so on) used to predict where the satellite is. Transmit power and zero-Doppler times are not required inputs.
T8B07
What is Doppler shift in reference to satellite communications?
A. A change in the satellite orbit
B. A mode where the satellite receives signals on one band and transmits on another
C. An observed change in signal frequency caused by relative motion between the satellite and Earth station ✓ Correct answer
D. A special digital communications mode for some satellites
Doppler shift is the apparent change in frequency caused by relative motion between the satellite and your station. The frequency is higher as the satellite approaches and lower as it recedes. It does not change the orbit.
T8B08
What does it mean if a satellite is operating in U/V mode?
A. The satellite uplink is in the 15-meter band and the downlink is in the 10-meter band
B. The satellite uplink is in the 70-centimeter band and the downlink is in the 2-meter band ✓ Correct answer
C. The satellite operates using ultraviolet frequencies
D. The satellite frequencies are usually variable
In satellite mode names, the first letter is the uplink band and the second is the downlink band. U/V means the uplink is UHF (70 cm) and the downlink is VHF (2 meters). It has nothing to do with ultraviolet.
T8B09
What causes spin fading of satellite signals?
A. Circular polarized noise interference radiated from the sun
B. Rotation of the satellite and its antennas ✓ Correct answer
C. Doppler shift of the received signal
D. Interfering signals within the satellite uplink band
Spin fading happens because the satellite and its antennas rotate, so the polarization and pattern presented to you change periodically and the signal rises and falls. It is not caused by Doppler shift, solar noise or uplink interference.
T8B10
What does the term LEO mean in reference to communication satellites?
A. Low Energy Orbit, which conserves battery power
B. Low Elevation Orbit, which appears close to the horizon from the earth station
C. Low Equilibrium Orbit, which has a slightly unstable period
D. Low Earth Orbit, which has a period of around 100 minutes ✓ Correct answer
LEO stands for Low Earth Orbit. Satellites in LEO circle the Earth in roughly 100 minutes, so each is overhead for only a short pass. The other expansions are invented terms.
T8B11
Who is permitted to receive telemetry from an amateur radio satellite?
A. Anyone ✓ Correct answer
B. Only the satellite control operator
C. Only the control operator or a licensed radio amateur who has received the encryption key from the control operator
D. Only a licensed radio amateur who has received the encryption key from AMSAT
Anyone may receive amateur satellite telemetry; its formats are generally published so listeners can decode it. Part 97 lets only telecommand signals sent up to a satellite be coded to hide their meaning (§97.211), so no encryption key from the control operator or AMSAT is needed to receive telemetry.
T8B12
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?
A. Check your signal strength report in the telemetry data
B. Listen for distortion on your downlink signal
C. Your signal strength on the downlink should be about the same as the beacon ✓ Correct answer
D. Compare your signal to others on the downlink using an internet SDR receiver
A linear transponder retransmits what it hears, so your downlink signal should be about as strong as the satellite's beacon. If it is much stronger, you are using too much uplink power and hogging the transponder.