3D1X3 Self Test Questions Vol. 3 Unit 2

Front 1

What usable frequency range propagates through the earth’s atmosphere?

Back 1

30 to 100.000 MHz (VHF to EHF).

Front 2

At what altitude are most geosynchronous satellites placed?

Back 2

22,582 miles above the earth.

Front 3

What are the terms for the nearest and farthest distances a satellite’s orbit comes to the earth?

Back 3

Perigee (nearest); apogee (farthest).

Front 4

What directions are descending and ascending nodes going?

Back 4

A satellite ascends when it travels northward and descends when it travels southward.

Front 5

Explain the term “slant range.”

Back 5

Attitude control and station keeping.

Front 6

Name the two types of orbital control used on satellites.

Back 6

(1) Spin stabilization.
(2) Gravity gradient.
(3) Momentum storage.
(4) Mass expulsion.
(5) Mixed systems.

Front 7

What are the five types of attitude control?

Back 7

7. The distance from the site to the satellite.

Front 8

How is tracking a satellite accomplished?

Back 8

8. By using a transponder.

Front 9

What terms describe the capabilities of communications satellites?

Back 9

Passive and active.

Front 10

What are the advantages of the passive satellite?

Back 10

Simplicity, wider frequency range, and multiple accesses.

Front 11

What are the disadvantages of passive satellites?

Back 11

Larger required transmitter power, larger antenna systems, more sensitive receiving equipment, and a larger
satellite size.

Front 12

What does the use of active communications satellites make possible?

Back 12

The use of smaller ground terminals.

Front 13

Name the two types of active satellites.

Back 13

Delay and real-time.

Front 14

What disadvantages does CDMA present?

Back 14

CDMA doesn’t use the power and frequency spectrum resources as effectively as does FDMA or TDMA,
and it requires complex equipment at both ends of the link.

Front 15

What’s the difference between TDMA and DAMA?

Back 15

In TDMA, users have a dedicated time slot, whether they use it or not; in DAMA, the dedicated time slot
can be used by other low-priority users when it isn’t in use.

Front 16

State the purpose of DAMA.

Back 16

To allocate and share satellite bandwidth on a demand-assigned basis.

Front 17

What does the network control system do with a call?

Back 17

Determines if the call is valid and establishes the channel between the originating site and the called site.

Front 18

What component may function as a network control system?

Back 18

Any unit with the required hardware and software.

Front 19

What’s the primary disadvantage of DAMA?

Back 19

Delay in service, particularly to lower-priority users.

Front 20

What information do you need to make manual look angle calculations?

Back 20

Latitude, longitude, and height of the satellite; latitude and longitude of your terminal; a calculator with
scientific functions or a natural sine, cosine, and tangent chart.

Front 21

When making calculations, how are ground distances measured on the earth's surface?

Back 21

In degrees, where 1° of arc equals 69 statute miles.

Front 22

What must you do after finding the general direction from the ground terminal to the satellite (the
calculated azimuth angle)?

Back 22

You have to apply a correction factor to get the correct azimuth look angle.

Front 23

Which time scale is equal to mean solar time when you make the correction at the zero meridian
in Greenwich, England?

Back 23

Universal time (UT0).

Front 24

How is atomic time obtained?

Back 24

From counting cycles of a signal from an atomic frequency source.

Front 25

Why do atomic time scales give us very accurate time of day?

Back 25

Because they use very stable atomic oscillators.

Front 26

What are the characteristics of UTC that give us a universally agreed to standard time scale that
we can depend on?

Back 26

The stability and accuracy of atomic time and synchronous operation with the earth’s motion about the sun
as in solar timekeeping.

Front 27

What kind of clock system is UTC?

Back 27

24-hour.

Front 28

Where is UTC referenced? To what is it referred?

Back 28

The zero meridian in Greenwich, England. Zulu time.

Front 29

By international agreement, all UTC time scales must agree with the UTC time scale operated by
the BIPM to within how many milliseconds?

Back 29

±1 ms.

Front 30

What is the USNO’s primary responsibility?

Back 30

Making astronomical observations to determine UT1 for navigation purposes and to keep atomic frequency
sources running for use by the DOD

Front 31

Which organization maintains our nation’s primary time/frequency standard?

Back 31

NIST.

Front 32

How does NIST distribute most time and frequency data?

Back 32

By radio.

Front 33

What are four uses of precision timing?

Back 33

(1) Correlate test data from several instrumentation locations.
(2) Start and stop programmed instruments.
(3) Synchronize range instrumentation.
(4) Control firing operations.

Front 34

List some examples of when timing errors must be reduced.

Back 34

When predicting a missile’s flight path, predicting satellite tracking coordinates, and uploading navigation
data to a satellite.

Front 35

Define primary frequency standard.

Back 35

A device used as the sole calibration reference for other frequency sources.

Front 36

Against what is a secondary frequency standard calibrated?

Back 36

A primary frequency standard.

Front 37

Describe the piezoelectric effect of quartz crystals.

Back 37

Mechanical compression of the crystal generates a charge across the crystal; conversely, the application of
an external voltage across the crystal causes it to expand or contract depending on the polarity of the
voltage.

Front 38

What two factors influence quartz oscillator performance?

Back 38

Temperature and aging.

Front 39

What are the two solutions for the crystal oscillator temperature dependence?

Back 39

(1) Enclosing the crystal in an electronically regulated oven.
(2) Using a temperature-compensated crystal oscillator.

Front 40

What are two of the most common types of atomic oscillators?

Back 40

(1) Rubidium gas cell.
(2) Cesium beam oscillators.

Front 41

What kind of frequency standard are cesium oscillators considered to be?

Back 41

Primary.

Front 42

Describe the overall purpose of the modem.

Back 42

An modem is a device that converts digital signals into analog signals and analog signals into digital
signals.

Front 43

What tasks do the modulator (transmitter) and the demodulator (receiver) perform?

Back 43

The modulator converts the digital data into an analog signal, which is suitable for transmission over
telephone lines or radio links. The demodulator receives the telephone or radio transmissions and converts
the audio signal back to the digital data

Front 44

Define multiplexing.

Back 44

The combination of two or more signals into a single signal for transmission over a medium.

Front 45

What is a multiplexer and what additional devices do fiber-optic multiplexers contain?

Back 45

Any device that permits the combination of different signals onto a single line is called a multiplexer. The
multiplexer provides various connectors to accept signals from multiple users and contains the circuitry to
combine multiple channels into an aggregate output. Fiber-optic multiplexers contain both source and
detector modems to provide transmit and receive capabilities over the fiber-optic link

Front 46

What multiplexing process assigns parts of each voice channel to specific time slots?

Back 46

Time division multiplexing (TDM).

Front 47

What standard uses time division multiplexing and makes better use of the increased bandwidth
available in fiber optics?

Back 47

Synchronous optical network (SONET).

Front 48

Describe wavelength division multiplexing.

Back 48

WDM assigns each incoming optical signal to a specific frequency of light (wavelength) within a certain
frequency band. The signals are carried down the fiber simultaneously, but each signal is independent from
the others.

Front 49

Beside higher data rates, what other features does dense wavelength division multiplexing
provide?

Back 49

The ability to amplify all the wavelengths at once without first converting them to electrical signals, and the
ability to carry signals of different speeds and types simultaneously and transparently over the fiber
(protocol and bit rate independence).