CDC 3D153 v3 Flashcards
State the types of traffic an AN/TRC–170 radio terminal set might handle.
Dedicated traffic such as analog and digital channels, point-to-point circuits, facsimile circuits, and teletype circuits.
List the equipment included in an AN/TRC–170 tropospheric scatter terminal.
Antennas, transmitting and receiving equipment, digital multiplexing equipment, voice and data orderwire facilities, built-in test equipment, and communications security equipment.
List the data rates processed by the tropospheric scatter modem.
Mission traffic at 128 through 4,096 Kbps in the 512 data rate family, and 72 through 4,608 Kbps in the 576 data rate family.
Describe the upconversion process of the transmit amplifier.
The IF signal is upconverted in the transmit amplifier converter by mixing it with a local oscillator input from the synthesizers. The difference frequency is selected as the final transmit frequency of 4.4 to 5.0 GHz.
Explain the difference in the transmission power requirements between tropospheric scatter and line-of-sight.
The HPA is necessary for transmission in the tropospheric scatter mode (1 kW, 60 dBm). It is also possible to transmit in LOS mode by not using the klystron. The output is 29 dBm (800 mW).
What is the minimum spacing used to separate receive antennas in space diversity, and what is the most common amount of antenna separation used?
Minimum of 50 wavelengths; common receive antenna spacing is 100 or more wavelengths.
What principle of propagation does frequency diversity use to its advantage?
Frequency diversity uses the principle that two different microwave frequencies fade independently of each other even though they travel the same propagation path.
What is the ideal frequency separation in frequency diversity?
A separation of 5 percent is ideal.
Define polarization diversity.
In polarization diversity, the same frequency radiates simultaneously in two different planes: horizontal and vertical.
Explain quadruple diversity.
Quadruple diversity is a technique that employs a combination of two or more of the diversity types: a combination of frequency and space diversity or space and polarization diversity—or a system that uses four reception paths.
Explain the purpose of the digital data group modem.
It interfaces up to four groups of conditioned diphase signals, or up to four groups of dipulse signals, or a mixture of the two.
Describe the main purpose of the digital data group modem.
Primarily, it changes cable-side conditioned diphase or dipulse signals to balanced NRZ signals, and vice versa.
Describe the purpose of the low-speed cable driver modem.
Changes the cable-side conditioned diphase signal to NRZ for use by the AN/TRC–170 and supplies power to cable low-speed pulse restorers if required.
What data rates are used by the low-speed cable driver modem?
It accepts data at 72 to 2,048 Kbps on the equipment side; 2,304 Kbps on the cable side.
What is the range of the low-speed cable driver modem with and without pulse restorers?
Up to 40 miles with pulse restorers and 1 mile without pulse restorers.
Describe the capabilities of the trunk group multiplexer.
It multiplexes up to four groups of the 512 Kbps data rate families or four groups of 576 Kbps data rate families into one supergroup. It will not process group data rates from both families simultaneously. It demultiplexes a supergroup into separate groups at their original data rates. It can control a KG–81 trunk encryption device on both the group and supergroup side.
Describe the purpose of the KG–81 trunk encryption device.
Full-duplex encryption and/or decryption of group or supergroup mission traffic.
Describe the purpose of the KG–84 dedicated loop encryption device and the KG–84A general purpose encryption equipment.
Encrypts and/or decrypts telemetry data, processed through the alarm monitor.
Describe the purpose of the KY–58 VINSON.
Encrypts and/or decrypts digital voice orderwire traffic originating and terminating at the voice orderwire control unit.
What is the purpose of the baseband patch panel?
Connects the digital group multiplex equipment with the tropospheric scatter modem.
Describe the three divided fields of the baseband patch panel.
- The upper jack field provides timing and data connections for the trunk group multiplexer, tropospheric scatter modem, and trunk encryption device 1. The right side provides patching for black station clock. Also provided are convenience patch groups A, B, and C, that are internally hard-wired to jacks in the center jack field.
- The center jack field provides connections to the equipment side of the loop group multiplexers, group modem groups, and the low-speed cable driver modem. The black side of the trunk encryption device 2 is also available. The dejitterizer input and/or output jacks provide for patching a group timingsignal directly into the tropospheric scatter modem. Inputs to trunk group multiplexer groups 3 and 4are available. Convenience patch groups A, B, and C pass data and timing signals to the upper jackfield.
- The lower jack field provides data orderwire connections for through patching or patching to and/or from the dedicated loop encryption device patch panel by way of the level converter jacks. Also
provided are connections for the digital voice orderwire and resync commands to the group and super group trunk encryption devices.
Describe the purpose of the dedicated loop encryption device patch panel.
Provides for patching the local telemetry signals to the radio and/or cable side of the AN/TRC–170 and for monitoring baseband and dedicated loop encryption device patch panel activity.
Describe the data rates of the tropospheric scatter modem.
128 through 4,096 Kbps in the 512 data rate family and 72 through 4,608 Kbps in the 576 Kbps data rate family.
List the types of inputs to the tropospheric scatter modem.
Mission data, digital voice orderwire, and up to four data orderwires.
What is the purpose of the loop back circuit in the IF patch panel?
Provides a calibrated means of applying the tropospheric scatter modem modulator IF output to tropospheric scatter modem demodulator inputs.
Why are the IF patch panels between the AN/TRC–170 V2 and V3 terminals not interchangeable?
The IF test panels are configured differently for each terminal.
Describe the outputs of the electrical frequency synthesizer.
Stable outputs in the 4.47 to 5.07 GHz range.
List the major subassemblies of the RF HPA and state their purpose.
- The microwave subassembly consists of a klystron amplifier, tuning, and built-in test equipment circuitry. The klystron is a continuous-wave, HPA that is air-cooled and mechanically tunable. It is bypassed, and the high voltage power supply is not used when operating in the LOS mode.
- The high voltage power supply provides beam and filament voltages for the klystron.
- The diplexer enables the transmitter and a receiver to operate from a common antenna port. The diplexers are used in the V2 model only.
Describe the purpose of the downconverters.
They preselect, amplify, and postselect the received microwave signal. The LNA and mixer combine the 4.4 to 5.0 GHz receive signal with a 4.47 to 5.07 GHz signal from the synthesizer to produce the 70 MHz
IF.
How does the alarm monitor determine overall system performance?
Equipment status information and performance data from all major components are reported to the alarm
monitor by the built-in test equipment circuits in each major subassembly. The data is sampled, processed, and evaluated. From this, overall system performance is determined.
List the orderwires and orderwire control units and describe each.
- The data orderwire consists of a 20-character telemetry status message that can be combined with a 12-telemetry status message from other stations to form a 2 Kbps composite bit stream that is transmitted to the communication nodal control element.
- The voice orderwire control unit connects a VINSON secure voice instrument with the 16 Kbps digital voice orderwire. This is a first-come, first-served party line system. The unit’s electronic bridge provides a through connection between the group modems and low-speed cable driver modem or tropospheric scatter modem.
- The remote orderwire control unit accesses the digital voice orderwire through the voice orderwire control unit. It does not provide secure voice transmission to the voice orderwire control unit.
- The analog voice orderwire (the maintenance orderwire) provides unencrypted, full-duplex voice connection with analog voice orderwire channels of the group modem and low-speed cable driver modem. It does not connect to the radio side of the AN/TRC–170 terminal.
What else does the power entry panel provide power to besides the equipment in the van?
The environmental control unit, an external convenience outlet, antenna feedhorn deicers, as well to as an external main breaker that controls the entire panel.
Describe how a surge protection circuit is used and whether it is required for an AN/TRC–170 terminal.
It is placed across each phase and the neutral line. It is not required for the van to operate, but without it there is no prime power surge protection.
List the functions of the power distribution unit.
It provides a central location to control equipment using primary power for fast power-up and power-down. It also powers the utility and convenience outlets and ceiling lighting. The front panel meters indicate current, voltage, and frequency.
Describe the purpose of the AC-AC converters.
They change the incoming AC signal to a 255 Vpp, 400 Hz quasi-square wave in order to operate the cooling fans in the shelter. AC-AC converter 1 runs all the blowers in the van, except those in RF HPA#2, these are run by AC-AC converter 2.
List the components and describe the function of the lightning protection assembly.
It consists of two, four-section telescoping masts approximately 30 feet tall (assembled), a sky wire 135 feet long, six anchors, two ground rods, and two mast base plates. The masts are installed 65 feet apart and slightly behind the two antennas. The sky wire is suspended between the two masts and is grounded on both ends. The lightning protection assembly acts as a large lightning rod by being the highest point at your station.
Describe the RF output power and frequency band of the TSSR.
14.4 to 15.25 GHz with RF output power of about 300 mW.
What are the two TSSR antenna lengths, and what are their maximum ranges?
1 foot and 2 feet; 10 and 25 miles respectively.
List the TSSR conditioned diphase waveform voltage and data rate.
3 Vpp conditioned diphase waveform ranging from 72 to 4,608 Kbps.
What is the maximum distance the TSSR’s RF and baseband assembly can be physically separated from each other, using the supplied cable?
150 feet.
What is the gain of the TSSR’s 1-foot antenna?
31 dB.
What is the gain of the TSSR’s 2-foot antenna?
37 dB.
What is the purpose of the input attenuator in the TSSR’s transmit baseband assembly?
Compensates for input signal amplitude variations caused by external equipment or varying cable lengths.
What is the transmitter deviation in the TSSR’s transmit baseband assembly?
±4 MHz.
What is the frequency of the transmitter subcarrier (orderwire) in the TSSR’s transmit baseband assembly?
8.5 MHz.
Describe the function of the TSSR’s diplexer.
It allows the use of a single piece of coaxial cable to pass the transmitter baseband signal from the baseband assembly to the RF assembly. Also transmitted on the same cable is the receiver 70 MHz IF signal from the RF assembly to the baseband assembly.
In the TSSR’s RF assembly, what is the frequency of the voltage-controlled oscillator, and how is its accuracy maintained?
7 GHz; by a phase-locked loop.
What is the purpose of the circulator in the TSSR’s RF assembly?
Permits the transmitter and receiver to be connected to the same antenna.
In the TSSR’s RF assembly, at what frequency is the tunable filter set?
Receive frequency.
How is noise generated by the transmitter prevented from interfering with the receiver, in the TSSR’s RF assembly?
The combination of tunable filter and three-port circulator is used to form a notch filter. The notch filter is tuned to the receiver’s frequency to reduce any noise generated by the transmitter that could interfere with the receiver.
Describe the frequency conversion process in the TSSR’s receive section.
The 14.4 to 15.25 GHz RF is mixed with the local oscillator frequency to produce a 70 MHz IF. The local oscillator frequency is always on the low side of the signal; that is, the local oscillator frequency equals the signal frequency minus 70 MHz.
What is the bandpass frequency range of the 70 MHz IF in the TSSR’s control and distribution unit?
20 MHz.
Which unit compensates for changes in the interconnecting cable length in the TSSR’s receive baseband assembly?
Automatic gain control amplifier.
In the TSSR’s receive baseband assembly, what type of waveform and data rate is used when operating in the fiber optic mode?
NRZ digital signals at a 6.144 Mbps rate.
What type of orderwire capability does the TSSR provide?
Full-duplex voice communication.
What usable frequency range propagates through the earth’s atmosphere?
30 to 100.000 MHz (VHF to EHF).
At what altitude are most geosynchronous satellites placed?
22,582 miles above the earth.
What are the terms for the nearest and farthest distances a satellite’s orbit comes to the earth?
Perigee (nearest); apogee (farthest).
What directions are descending and ascending nodes going?
A satellite ascends when it travels northward and descends when it travels southward.
Explain the term “slant range.”
The distance from the site to the satellite.
Name the two types of orbital control used on satellites.
Attitude control and station keeping.
What are the five types of attitude control?
- Spin stabilization.
- Gravity gradient.
- Momentum storage.
- Mass expulsion.
- Mixed systems.
How is tracking a satellite accomplished?
By using a transponder.
What terms describe the capabilities of communications satellites?
Passive and active.
What are the advantages of the passive satellite?
Simplicity, wider frequency range, and multiple accesses.
What are the disadvantages of passive satellites?
Larger required transmitter power, larger antenna systems, more sensitive receiving equipment, and a larger satellite size.
What does the use of active communications satellites make possible?
The use of smaller ground terminals.
Name the two types of active satellites.
Delay and real-time.
What disadvantages does CDMA present?
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.
What’s the difference between TDMA and DAMA?
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.
State the purpose of DAMA.
To allocate and share satellite bandwidth on a demand-assigned basis.
What does the network control system do with a call?
Determines if the call is valid and establishes the channel between the originating site and the called site.
What component may function as a network control system?
Any unit with the required hardware and software.
What’s the primary disadvantage of DAMA?
Delay in service, particularly to lower-priority users.
What information do you need to make manual look angle calculations?
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.
When making calculations, how are ground distances measured on the earth’s surface?
In degrees, where 1° of arc equals 69 statute miles.
What must you do after finding the general direction from the ground terminal to the satellite (the calculated azimuth angle)?
You have to apply a correction factor to get the correct azimuth look angle.
Which time scale is equal to mean solar time when you make the correction at the zero meridian in Greenwich, England?
Universal time (UT0).
How is atomic time obtained?
From counting cycles of a signal from an atomic frequency source.
Why do atomic time scales give us very accurate time of day?
Because they use very stable atomic oscillators.
What are the characteristics of UTC that give us a universally agreed to standard time scale that we can depend on?
The stability and accuracy of atomic time and synchronous operation with the earth’s motion about the sun as in solar timekeeping.
What kind of clock system is UTC?
24-hour.
Where is UTC referenced? To what is it referred?
The zero meridian in Greenwich, England. Zulu time.
By international agreement, all UTC time scales must agree with the UTC time scale operated by the BIPM to within how many milliseconds?
±1 ms.
What is the USNO’s primary responsibility?
Making astronomical observations to determine UT1 for navigation purposes and to keep atomic frequency sources running for use by the DOD.
Which organization maintains our nation’s primary time/frequency standard?
NIST.
How does NIST distribute most time and frequency data?
By radio.
What are four uses of precision timing?
- Correlate test data from several instrumentation locations.
- Start and stop programmed instruments.
- Synchronize range instrumentation.
- Control firing operations.
List some examples of when timing errors must be reduced.
When predicting a missile’s flight path, predicting satellite tracking coordinates, and uploading navigation data to a satellite.
Define primary frequency standard.
A device used as the sole calibration reference for other frequency sources.
Against what is a secondary frequency standard calibrated?
A primary frequency standard.
Describe the piezoelectric effect of quartz crystals.
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.
What two factors influence quartz oscillator performance?
Temperature and aging.
What are the two solutions for the crystal oscillator temperature dependence?
- Enclosing the crystal in an electronically regulated oven.
- Using a temperature-compensated crystal oscillator.
What are two of the most common types of atomic oscillators?
- Rubidium gas cell.
2. Cesium beam oscillators.
What kind of frequency standard are cesium oscillators considered to be?
Primary.
Describe the overall purpose of the modem.
An modem is a device that converts digital signals into analog signals and analog signals into digital signals.
What tasks do the modulator (transmitter) and the demodulator (receiver) perform?
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.
Define multiplexing.
The combination of two or more signals into a single signal for transmission over a medium.
What is a multiplexer and what additional devices do fiber-optic multiplexers contain?
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.
What multiplexing process assigns parts of each voice channel to specific time slots?
Time division multiplexing (TDM).
What standard uses time division multiplexing and makes better use of the increased bandwidth available in fiber optics?
Synchronous optical network (SONET).
Describe wavelength division multiplexing.
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.
Beside higher data rates, what other features does dense wavelength division multiplexing provide?
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).
What is the purpose of the space segment?
To provide the downlink information encompassing an area of coverage required by the program mission or the program Operational Requirements Document.
Define telemetry?
The science of measuring physical properties and other phenomena onboard mission satellites and transmitting these measurements to ground receiving elements.
What types of information do the telemetry, tracking, and command status contain?
Data on the receiver and demodulator units, command decryptor unit, downlink transmitter, telemetry formatting and encoding unit, telemetry encryptor, and satellite antenna configuration.
What are the two major sections of a basic satellite?
- The mission (or missions) payload.
2. The spacecraft bus.
Why is stability important to the satellite?
Because it allows the payload to operate with accuracy and the satellite bus to receive commands and uploaded data with reliability.
For what types of satellites are position and orientation control especially critical?
Those using highly directional antennas.
What is the function of the C2 segment?
To support the satellites and enhance the downlinked mission data for the user segment.
What do all satellites require, regardless of the program?
Telemetry, tracking and commanding support.
What is the purpose of antenna pointing data?
It is used to drive motors to move the antenna to the specific acquisition angles.
Why is satellite command verification so important?
To make sure commands have been executed properly.
Why is using the same reference time between the C2 segment and the satellite so important?
Without it, operations—such as commanding mission satellites, processing and evaluating tracking data, or processing telemetry data—would be impossible.
What is the purpose of the user segment?
To receive, process, use, or distribute mission data as required by program taskings.
What is the purpose of the DMSP user segment?
To receive, process, and distribute global weather data to support Air Force, Army, Navy, and Marine Corps operations worldwide.
In the DSP program, what agency operates SBIRS satellites?
The 460th Space Wing at Buckley AFB, Colorado.
Where do the DSP early warning centers forward their data?
To various agencies and operation areas around the world, varying with the Air Force’s changing mission.
What is the purpose of the GPS user segment?
To enable users to passively receive the satellite broadcast position, velocity, and time data for their operational mission.
What is the primary purpose of Milstar?
To support the National Command Authority and provide the Navy, Army, and Air Force with interoperable command, control, and communications (C3) at all levels of conflict for both strategic and tactical forces.
For what purposes do we use a satellite beacon?
To locate, identify, and track a satellite.
How does telemetry differ from the satellite beacons?
Telemetry refers to the data sent by the satellite to give on-board equipment status.
What is ephemeris data?
Data showing the calculated positions of a satellite at regular intervals of time.
How does computer programmed tracking differ from automatic signal tracking?
In computer programmed tracking, the position of the satellite is computed and the pointing signal is generated from that information. Automatic tracking follows the apparent position of the satellite based on the actual signals from the satellite.
Which autotracking method cannot sense the satellite location without moving off the satellite main beam?
Random step track.
What two IF frequencies are used by the DSCS earth terminal? What’s their nominal signal level?
(1) 70 MHz at –10 dBm.
(2) 700 MHz at –13 dBm.
How are the HPAs cooled in a DSCS earth terminal?
Air cooled.
