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Subelement E2
OPERATING PROCEDURES
Section E2A
Amateur radio in space: amateur satellites; orbital mechanics; frequencies and modes; satellite hardware; satellite operations; experimental telemetry applications
What is the direction of an ascending pass for an amateur satellite?
  • From west to east
  • From east to west
  • From south to north
  • From north to south

An astronomical object is Ascending when it is moving north in latitude with respect to the celestial sphere or "up" with respect to the usual ground map. Decending means moving south or "down" with respect to the map.

Most satellites (Including all amateur radio satellites which have ever been launched) move west to east or "prograde." To launch a satellite into a retrograde orbit is much more difficult and expensive and is typically only done for commercial or military earth observation satellites in order to maximize their coverage over the ground as retrograde orbits move faster with respect to the ground. There are no questions about retrograde or prograde orbits on the Element 4 exam, so this information is purely gratuitous.

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What is the direction of a descending pass for an amateur satellite?
  • From north to south
  • From west to east
  • From east to west
  • From south to north

The best way to remember this is to think of a map. Normally maps are held with north on top, so going "down" on the map is going from north to south.

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What is the orbital period of an Earth satellite?
  • The point of maximum height of a satellite's orbit
  • The point of minimum height of a satellite's orbit
  • The time it takes for a satellite to complete one revolution around the Earth
  • The time it takes for a satellite to travel from perigee to apogee

The definition of the word period in this case is a round of time marked by the recurrence of some phenomenon or occupied by some recurring process or action.

So, the "orbital period" is a round of time marked by the recurrence of the orbit of an earth satellite -- in other words, it's the time it takes for a satellite to complete one revolution around the Earth.

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What is meant by the term mode as applied to an amateur radio satellite?
  • The type of signals that can be relayed through the satellite
  • The satellite's uplink and downlink frequency bands
  • The satellite's orientation with respect to the Earth
  • Whether the satellite is in a polar or equatorial orbit

Historically OSCAR uplink (transmit to) and downlink (receive from) frequencies were designated using single letter codes.

Mode A: 2 m uplink / 10 m downlink

Mode B: 70 cm uplink / 2 m downlink

Mode J: 2 m uplink / 70 cm downlink

New uplink and downlink designations use sets of paired letters following the structure X/Y where X is the uplink band and Y is the downlink band.

Reference: http://en.wikipedia.org/wiki/OSCAR#Mode_designators

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What do the letters in a satellite's mode designator specify?
  • Power limits for uplink and downlink transmissions
  • The location of the ground control station
  • The polarization of uplink and downlink signals
  • The uplink and downlink frequency ranges

Historically OSCAR uplink (transmit to) and downlink (receive from) frequencies were designated using single letter codes.

Mode A: 2 m uplink / 10 m downlink Mode B: 70 cm uplink / 2 m downlink Mode J: 2 m uplink / 70 cm downlink

New uplink and downlink designations use sets of paired letters following the structure X/Y where X is the uplink band and Y is the downlink band.

Reference: http://en.wikipedia.org/wiki/OSCAR#Mode_designators

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On what band would a satellite receive signals if it were operating in mode U/V?
  • 435 MHz - 438 MHz
  • 144 MHz - 146 MHz
  • 50.0 MHz - 50.2 MHz
  • 29.5 MHz - 29.7 MHz

The paired letters U/V indicate the uplink (receive) and downlink (transmit) bands that the satellite uses, where:

  • U - 70 cm (in the UHF range)
  • V - 2 m (in the VHF range)

See Wikipedia's page on amateur radio satellite a complete list of mode designators.

The order is uplink/downlink, which from the perspective of the satellite is receive/transmit.

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Which of the following types of signals can be relayed through a linear transponder?
  • FM and CW
  • SSB and SSTV
  • PSK and Packet
  • All of these choices are correct

A linear transponder takes one range of frequencies and directly shifts it to another range, without decoding and re-encoding the signals. Therefore, any signal type that fits in the transponder's bandwidth can be used through it.

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Why should effective radiated power to a satellite which uses a linear transponder be limited?
  • To prevent creating errors in the satellite telemetry
  • To avoid reducing the downlink power to all other users
  • To prevent the satellite from emitting out-of-band signals
  • To avoid interfering with terrestrial QSOs

Satellite transponders are power-sharing. If one signal is received at the satellite is stronger than the others, all other retransmitted signals will get a smaller portion of the available power.

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What do the terms L band and S band specify with regard to satellite communications?
  • The 23 centimeter and 13 centimeter bands
  • The 2 meter and 70 centimeter bands
  • FM and Digital Store-and-Forward systems
  • Which sideband to use

Transponder link designators:

Frequency Designator
21Mhz H
29Mhz/ T
145Mhz/ V
435Mhz/ U
**1.2Ghz/ L**
**2.4Ghz/ S**
5.7Ghz/ C
10.5Ghz/ X
24Ghz/ K

-w3mit


Study Hint: Think "(L)ittle and (S)mall" for 23 and 13 cm.

See the mode designator chart

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Why may the received signal from an amateur satellite exhibit a rapidly repeating fading effect?
  • Because the satellite is spinning
  • Because of ionospheric absorption
  • Because of the satellite's low orbital altitude
  • Because of the Doppler Effect

Many amateur radio satellites are spinning either as a form of stabilization or because of reduced ability to control attitude due to their small size and power budget compared to larger commercial satellites. When the satellite's antenna is spinning relative to a fixed ground antenna, fading can occur.

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What type of antenna can be used to minimize the effects of spin modulation and Faraday rotation?
  • A linearly polarized antenna
  • A circularly polarized antenna
  • An isotropic antenna
  • A log-periodic dipole array

The most common polarizations we think of are "vertical" and "horizontal" polarization; spin modulation and faraday rotation have the result that whatever the polarization it will generally not be "ideal" for the other side of the communication (this is an oversimplification, but helps for understanding).

A circularly polarized antenna results, in effect, in a signal which is constantly changing the specific direction of polarization; as such, while it may not be perfectly ideal to communicate with any other type of antenna, it will never be perfectly not ideal for any antenna either, i.e. it will be ideal for a certain percentage of the time.

It may help to remember: "spin", "rotation", and "circularly".

For more information, see the wikipedia article on Circular Polarization

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What is one way to predict the location of a satellite at a given time?
  • By means of the Doppler data for the specified satellite
  • By subtracting the mean anomaly from the orbital inclination
  • By adding the mean anomaly to the orbital inclination
  • By calculations using the Keplerian elements for the specified satellite

(D) By calculations using the Keplerian elements for the specified satellite.

Keplerian elements are the inputs to a standard mathematical model of spacecraft orbits. Most often the calculations needed would include the Keplerian elements, an accurate time clock and your current location.

AMSAT Info on Keplerian elements

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What type of satellite appears to stay in one position in the sky?
  • HEO
  • Geostationary
  • Geomagnetic
  • LEO

A geosynchronous satellite is actually moving along its orbit just like any other satellite. It is at a height and position such that this orbital rotation matches the earth’s rotation and so it appears to be stationary.

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What technology is used to track, in real time, balloons carrying amateur radio transmitters?
  • Radar
  • Bandwidth compressed LORAN
  • APRS
  • Doppler shift of beacon signals

http://www.aprs.org/

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications of information of immediate value in the local area. In addition, all data is ingested into the APRS Internet System (APRS-IS) and distributed globally for immediate access. Shared information contains global coordinates, altitude, speed, heading, text messages, alerts, announcements, and bulletins. The most visible aspect of APRS is its capability of map display. Anyone may place any object or information on the map, and it is distributed to all maps of all users in the local RF network, or to anyone monitoring the area via the Internet. Any station, radio, or object broadcasting GPS coordinates to the APRS system can be automatically tracked over time.

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