Term
| 403-1. What usable frequency range propagates through the earth’s atmosphere? |
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Definition
| 30 to 100.000 MHz (VHF to EHF). |
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Term
| 403-2. At what altitude are most geosynchronous satellites placed? |
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Definition
| 22,582 miles above the earth. |
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Term
| 403-3. What are the terms for the nearest and farthest distances a satellite’s orbit comes to the earth? |
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Definition
| Perigee (nearest); apogee (farthest). |
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Term
| 403-4. What directions are descending and ascending nodes going? |
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Definition
| A satellite ascends when it travels northward and descends when it travels southward. |
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Term
| 403-5. Explain the term “slant range.” |
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Definition
| Attitude control and station keeping. |
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Term
| 403-6. Name the two types of orbital control used on satellites. |
|
Definition
(1) Spin stabilization.
(2) Gravity gradient.
(3) Momentum storage.
(4) Mass expulsion.
(5) Mixed systems. |
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Term
| 403-7. What are the five types of attitude control? |
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Definition
| The distance from the site to the satellite. |
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Term
| 403-8. How is tracking a satellite accomplished? |
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Definition
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Term
| 404-1. What terms describe the capabilities of communications satellites? |
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Definition
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Term
| 404-2. What are the advantages of the passive satellite? |
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Definition
| Simplicity, wider frequency range, and multiple accesses. |
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Term
| 404-3. What are the disadvantages of passive satellites? |
|
Definition
Larger required transmitter power, larger antenna systems, more sensitive receiving equipment, and a larger
satellite size. |
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Term
| 404-4. What does the use of active communications satellites make possible? |
|
Definition
| The use of smaller ground terminals. |
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Term
| 404-5. Name the two types of active satellites. |
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Definition
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Term
| 405-1. What disadvantages does CDMA present? |
|
Definition
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. |
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Term
| 405-2. What’s the difference between TDMA and DAMA? |
|
Definition
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. |
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Term
| 405-3. State the purpose of DAMA. |
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Definition
| To allocate and share satellite bandwidth on a demand-assigned basis. |
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Term
| 405-4. What does the network control system do with a call? |
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Definition
| Determines if the call is valid and establishes the channel between the originating site and the called site. |
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Term
| 405-5. What component may function as a network control system? |
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Definition
| Any unit with the required hardware and software. |
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Term
| 405-6. What’s the primary disadvantage of DAMA? |
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Definition
| Delay in service, particularly to lower-priority users. |
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Term
| 406-1. What information do you need to make manual look angle calculations? |
|
Definition
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. |
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Term
| 406-2. When making calculations, how are ground distances measured on the earth's surface? |
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Definition
| In degrees, where 1° of arc equals 69 statute miles. |
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Term
406-3. What must you do after finding the general direction from the ground terminal to the satellite (the
calculated azimuth angle)? |
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Definition
| You have to apply a correction factor to get the correct azimuth look angle. |
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|
Term
407-1. Which time scale is equal to mean solar time when you make the correction at the zero meridian
in Greenwich, England? |
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Definition
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Term
| 407-2. How is atomic time obtained? |
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Definition
| From counting cycles of a signal from an atomic frequency source. |
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Term
| 407-3. Why do atomic time scales give us very accurate time of day? |
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Definition
| Because they use very stable atomic oscillators. |
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Term
407-4. What are the characteristics of UTC that give us a universally agreed to standard time scale that
we can depend on? |
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Definition
The stability and accuracy of atomic time and synchronous operation with the earth’s motion about the sun
as in solar timekeeping. |
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Term
| 408-1. What kind of clock system is UTC? |
|
Definition
|
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Term
| 408-2. Where is UTC referenced? To what is it referred? |
|
Definition
| The zero meridian in Greenwich, England. Zulu time. |
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Term
409-1. By international agreement, all UTC time scales must agree with the UTC time scale operated by
the BIPM to within how many milliseconds? |
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Definition
|
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Term
| 409-2. What is the USNO’s primary responsibility? |
|
Definition
Making astronomical observations to determine UT1 for navigation purposes and to keep atomic frequency
sources running for use by the DOD. |
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Term
| 409-3. Which organization maintains our nation’s primary time/frequency standard? |
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Definition
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|
Term
| 409-4. How does NIST distribute most time and frequency data? |
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Definition
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Term
| 409-5. What are four uses of precision timing? |
|
Definition
(1) Correlate test data from several instrumentation locations.
(2) Start and stop programmed instruments.
(3) Synchronize range instrumentation.
(4) Control firing operations. |
|
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Term
| 409-6. List some examples of when timing errors must be reduced. |
|
Definition
When predicting a missile’s flight path, predicting satellite tracking coordinates, and uploading navigation
data to a satellite. |
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Term
| 410-1. Define primary frequency standard. |
|
Definition
| A device used as the sole calibration reference for other frequency sources. |
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Term
| 410-2. Against what is a secondary frequency standard calibrated? |
|
Definition
| A primary frequency standard. |
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Term
| 410-3. Describe the piezoelectric effect of quartz crystals. |
|
Definition
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. |
|
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Term
| 410-4. What two factors influence quartz oscillator performance? |
|
Definition
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|
Term
| 410-5. What are the two solutions for the crystal oscillator temperature dependence? |
|
Definition
(1) Enclosing the crystal in an electronically regulated oven.
(2) Using a temperature-compensated crystal oscillator. |
|
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Term
| 410-6. What are two of the most common types of atomic oscillators? |
|
Definition
(1) Rubidium gas cell.
(2) Cesium beam oscillators. |
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|
Term
| 410-7. What kind of frequency standard are cesium oscillators considered to be? |
|
Definition
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|
Term
| 411-1. Describe the overall purpose of the modem. |
|
Definition
An modem is a device that converts digital signals into analog signals and analog signals into digital
signals. |
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Term
| 411-2. What tasks do the modulator (transmitter) and the demodulator (receiver) perform? |
|
Definition
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. |
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Term
| 412-1. Define multiplexing. |
|
Definition
| The combination of two or more signals into a single signal for transmission over a medium. |
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Term
| 412-2. What is a multiplexer and what additional devices do fiber-optic multiplexers contain? |
|
Definition
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. |
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Term
| 412-3. What multiplexing process assigns parts of each voice channel to specific time slots? |
|
Definition
| Time division multiplexing (TDM). |
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|
Term
412-4. What standard uses time division multiplexing and makes better use of the increased bandwidth
available in fiber optics? |
|
Definition
| Synchronous optical network (SONET). |
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Term
| 412-5. Describe wavelength division multiplexing. |
|
Definition
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. |
|
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Term
412-6. Beside higher data rates, what other features does dense wavelength division multiplexing
provide? |
|
Definition
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). |
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