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116 Cards in this Set

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(823) What effectively eliminates moving target indicator (MTI)blind speeds at the speeds seen in air traffic control?
Staggered pulse repetition frequency (PRF)
(823) What circuit in the AN/GPN-20 ASR re-aligns the staggered pulse recurrence times (PRTs) back to the average PRT?
MTI and normal alignment circuit.
(823) A dual-frequency diversity configuration of transmitter and receiver pairs provides a capability to operate each system __________ with __________ antenna(s).
both systems simultaneously with one antenna.
(823) In dual diversity mode, the overall system timing is derived from....
the selected master channel.
(824) In the AN/GPN-20 ASR transmitter, what causes the magnetron to oscillate?
A high voltage negative pulse
(824) What is used to regulate the output of the transmitter's high voltage power supply?
Conduction time of six silicon controlled rectifiers (SCRs)
(824) What is the origin and name of the signal that discharges the four pulse modules?
modulator control assembly and PRE RF trigger
(824) The component that provides the proper hold-off time necessary for spreading of the silicon controlled rectifier (SCR) junction conductive area and permits the complete transfer of energy from the pulse modules into the pulse forming network (PFN) is the
hold-off inductor
(824) Which assembly ensures that the level of charge on the PFN is the same from PRT to PRT, regardless of the duration?
De-Quing control assembly
(824) A 3x fault with turn off the high voltage power supply and not automatically turn the transmitter back on if the same 3x fault occurs...
three times within a 61 second sample period
(825) Which component consists of two radio frequency (RF) filters?
diplexer
(826) Radio frequency (RF) to the antenna makes the transition from fixed to rotating waveguide within the
rotary joint
(826) When the horizontal plane of the transmitted beam of an ASR is on a target for less time, the
greater the azimuth resolution
(826) How many feedhorns does the AN/GPN-20 ASR use to both transmit and receive?
One
(826) The ASR antenna is always aligned to...
magnetic north
(826) How many azimuth change pulses (ACP's) are generated per antenna revolution?
4096
(826) In an ASR antenna system, when is circular polarization used?
during inclement weather conditions
(827) The low-power phase shifter is adjusted by a
tuning knob positioned on the same section of waveguide
(827) Most of the crystal current flowing in a signal mixer is generated by the
Receiver stable local oscillator
(828) The normal IF amplifier provides IF
amplification, bandpass filtering, video detection, and video amplification
(828) Which is a weakness of the phase detector with respect to the coherent oscillator (COHO) and echo relationship?
Blind phase; phase relationship equals zero volts
(829) The phase of the locked COHO signal is determined by the
magnetron pulse
(829) Most moving target indicator (MTI) phase detectors are designed to develop a
triangular output characteristic
(830) The point at which sensitivity time control (STC) waveshape ends is the
RF or IF baseline
(831) What two signals are mixed in the automatic frequency control (AFC) mixer to produce a signal representative of the difference between the magnetron and STALO frequency?
Attenuated transmitter pulse and STALO signal
(831) At what limit from center frequency does the automatic frequency control (AFC) circuitry stop tuning and shut off the transmitter high voltage?
+- 4 MHz
(832) To condition the input video to the video processor, the moving target indicator (MTI) video conditioner card shifts the incoming video from a zero volt baseline to a
positive two volt baseline for analog to digital (A/D) conversion
(832) In the AN/GPN-20, moving target indicator (MTI) cancellation takes place in the
video processor cancellation circuits
(832) How many range cells long will the MTI LOG-FTC card eliminate blocks of weather clutter?
Nine
(832) The purpose of the ASR video processor enhancer circuit card is to
increase synchronous target intensity (aircraft returns), and remove nonsynchronous returns such as random noise
(832) In the ASR video processor, either the log or normal video is selected for the input to the MTI /normal enhancer circuit in the
normal log FTC circuit card
(832) The cascade canceller response s more desirable (lower response) for
slow speed moving targets
(832) If your base services slower-moving aircraft, which sub-clutter visibility mode would be the best to use?
25 db
(833) What function of the range azimuth gating (RAG) is used to indicate runway, air route, or approach pattern?
azimuth strobe gating
(833) Who initially determines area needs for the range azimuth gating circuits?
survey team
(833) For how many minutes is the control memory energized by the temporary power supply when a power failure occurs?
10 minutes
(833) Concerning ASR remoting, all control functions are sent through the
control encoder and decoder
(833) Who initially determines area needs for the range azimuth gating circuits?
survey team
[823] How does a staggered PRF effectively eliminate blind speed?
By introducing an apparent change in target speed.
[823] Define blind speed.
At target speed at which successive radar returns change phase by 180 degrees.
[823] How are triggers developed at specific times in the digital synchronizer?
Decoder gates initiate a trigger at predetermined counts.
[823] How are different PRFs selected?
By changing the count at which the reset pulse will start the count sequence again.
[823] How can two separate systems operate together through one antenna?
Diplexers isolate the frequency components of each channel while timing between the two is synchronized, one channel acting as the master, the other the slave.
[823] Why are there no phasing problems between the master and slave channel videos?
Both channel system clocks are derived from the same source.
[823] Master channel transmitter pulses occur how many microseconds before the slave channel pulses?
1.4 microseconds.
[824] What are the two trigger multiplying circuits prior to the magnetron called?
Modulator driver (containing modular control and trigger amplifier circuits) and the modulator itself
[824] In the AN/GPN-20, what signal discharges the four pulse modules?
The silicon controlled rectifier (SCR) gate
[824] How is the output of the HVPS regulated?
By controlling the amount of conduction time for each of the six Silicon Controlled Rectifiers (SCRs). Increasing or decreasing the amount of time they are gated on will increase of decrease the output voltage.
[824] What signal does the modulator control use to initiate the actual firing of the transmitter?
The PRE RF TRIGGER.
[824] What happens to the transmitter when one pulse module fails?
The transmitter continues to operate at a lower power level.
[824] What is the output of the magnetic pulse modulator?
A narrow (0.8 usec) negative 5.5kV pulse sent to the pulse transformer.
[824] Why do we control the amplitude of the pulse modulator output?
To provide superior frequency stability and improved operation of MTI receiver circuits.
[824] What is the average value for magnetron current and what does it indicate?
The average approximate value is 30mA; Its a good indicator of transmitter output power.
[824] How long does the sample period for a 3X fault last from the beginning of the first fault indication?
61 seconds
[825] What does a duplexer do?
It allows the use of a single antenna for both transmitting and receiving.
[825] Explain the difference between ASR high-power and low-power diplexers.
High power is pressurized an suitable for both transmit and receive signals; low power is suitable for received signals only.
[825] What application does the diplexer have in the AN/GPN-20 radar?
It allows two channels with different frequencies to operate using one antenna. This frequency diversity greatly improves target detection.
What are the two functions of the filters in the diplexer?
(1) Isolation between channels
(2) They filter magnetron side lobes.
[826] Describe the function of the Pedestal as an antenna unit.
It supports the antenna.
[826] Describe the function of the Encoder as an antenna unit
Produces azimuth data
[826] Describe the function of the Reflector as an antenna unit
Shapes the RF pattern into a narrow beam.
[826] Describe the function of the Feedhorn as an antenna unit
Radiates RF energy toward the reflector.
[826] Describe the function of the Polarizer as an antenna unit
Selects the mode of radiation (circular or linear).
[826] What device is used to make the transition from fixed waveguide to rotating waveguide?
Rotary joint
[826] What can be done to the antenna beam to increase the azimuth resolution?
Narrow the beam
[826] What three conditions must be met by the horizontal pattern of an ASR antenna for the most accurate indicator display?
(1) Narrow beam for azimuth resolution
(2) Optimum speed for consistent target presentation
(3) Constant speed for azimuth accuracy
[826] What is the purpose of the passive feedhorn?
It is a receive-only device that effectively raises the received beam pattern by 3.5° to reduce ground clutter.
[826] What could you expect if using the clutter reducing aspect of a dual-feedhorn system on a mountain range reaching 4° above the horizon?
The amount of clutter would be reduced by the amount which is below 3.5°.
[826] What are the two reasons for tilting the antenna?
(1) To minimize the affects of local terrain on the radiation pattern
(2) To improve the strength of the average return from an aircraft (making the strongest part of the radiation pattern coincide with the glide slope of a particular type of aircraft).
[826] How will the optimum antenna angle be determined?
A survey and flight check.
[826] Where are the encoders located in the AN/GPN-20 ASR?
In the rotary joint.
[826] What purpose do Azimuth Change Pulses (ACPs) and Azimuth Reference Pulses (ARPs) serve?
To synchronize the indicator sweep with the motion of the antenna?
[826] What does the step-twist section of waveguide provide?
A gradual twist between the waveguide feed and the rectangular transformer section.
[826] In what direction will the circular polarized reflected energy from a symmetrical target (rain drop) be polarized?
In the opposite direction of the transmitted energy.
[827] At what point in the RF return path is the active of passive return selected for processing?
The antenna patten switch.
[827] Why is the Low Noise Amplifier(LNA) placed ahead of the signal mixer?
To reduce the signal-to-noise ratio of the receiver.
[827] What does the AN/GPN-20 ASR use to accomplish RF to IF conversion?
The crossbar mixer
[827] What receiver component generates most of the crystal current in the signal mixer?
The Stable Local Oscillator (STALO)
[828] A preamplifier with a broad bandwidth is often preferable for what application?
MTI applications.
[828] What does the normal IF amplifier provide?
IF amplification, bandpass filtering, video detection, and video amplification.
[828] For what purpose is the log IF amplifier used in conjunction with circular polarization?
To prevent weather clutter from obscuring desired target returns on the PPI displays.
[828] What are the three separate signals applied to the MTI IF amplifier?
(1) The IF from the preamplifier.
(2) Reference (COHO) oscillations used in the phase detector.
(3) Lock test pulses, used only for testing.
[828] Why must all signals be the same amplitude when they leave the IF strip?
Because the phase detector is sensitive to an amplitude change as well as a phase change.
[828] Quadrature (Q)MTI is designed to overcome what weakness?
Blind Phase
[829] Within the phase detector the IF signals are compared in relative phase to what signal?
The COHO Oscillator signal.
[829] Just prior to firing the magnetron, the COHO is gated off by what trigger?
The PRE RF trigger
[829] The amplitude and polarity of the phase detector video output is dependent upon what?
The relative phase between the two IF input signals.
[830] What condition should the MTI IF gain be set for?
The best signal-to-noise ratio.
[830] What does the recovery slope on the STC wave shape represent?
The rate at which an STC wave shape increases video gain as range increases
[830] What factor determines the baseline of the STC waveform?
The baseline is set by the IF gain level and normally adjusted to maintain the rest of the received signal at optimum gain.
[830] What is the purpose of the Fast Time Constant (FTC) circuit?
It reduces the effects of large blocks of video, including precipitation clutter, by removing all of the video components, except, in some cases, for the leading or lagging edges.
[831] A relative (or difference) Automatic Frequency Control (AFC) circuit tunes what component to maintain a 30 MHz IF?
The magnetron
[831] The Automatic Frequency Control (AFC) error signal is derived form the difference between what signals?
The STALO output and an attenuated portion of the transmitter pulse.
[831] What is the output of the phase detector?
The phase detector circuit develops a positive or negative voltage, referenced to zero volts, and proportional to the IF pulse below or above 30 MHz.
[831] What is the area of no correction called?
The null or dead zone.
[831] What happens when the ASR transmitter frequency drifts more than 4 MHz from its normal frequency?
When the frequency error shifts the system will track back up to 4 MHz, above or below operating frequency. If the frequency exceeds that threshold the AFC circuitry stops tuning and shuts down the transmitter.
[831] What happens to the frequency error signal in manual operation?
The error voltage is disconnected when going to the manual control position.
[831] What subassemblies does the log test generator module contain?
(1) Noise generator assembly
(2) Random speed target generator subassembly.
[831] What is the purpose of the log test generator outputs?
The processing of these signals by the receiver circuits permits evaluation of the receiver and processor circuit's.
[832] Where does the Master Timing Signal (PRFCK) originate from?
The continuously running 30-MHz crystal-controlled oscillator of MTI Control, A27 card.
[832] The 0.467 usec Range Cell (RC) provides range resolution of two targets separated in range by approximately how manny feet?
230 feet or more.
[832] What are the two functions of the MTI video conditioner?
It conditions the receiver coherent video and generates test signals to check the quantizers and dual cancellers.
[832] Define quantization.
It is the conversion of an analog signal to a digital signal, with steps between specified levels.
[832] What functions does the A48 MTI LOG-FTC card perform?
It eliminates blocks of weather clutter at least nine range cells long and delays all MTI words five range cells or 2.335 usec, even when the card is turned off.
[832] In what circuit card is either log or normal video selected?
The A32 Normal LOG-FTC card.
[832] What is the purpose of the Diversity Combiner A38 circuit card?
It combines master and slave channel videos.
[832] List three factors used to determine the radar's subclutter visibility.
(1) Pulse Repetition Frequency (PRF)
(2) Antenna bandwidth
(3) Speed of antenna rotation.
[832] Identify three types of canceller configurations.
(1) Single
(2) Cascade
(3) Cascade with feedback
[832] How does the single canceller response differ from the cascade canceller response.
The single canceller response is much greater for high-speed moving targets while cascade response has lower (more desirable) response to slow-speed moving targets.
[832] Define subclutter visibility.
It is a figure of merit for an MTI system, expressed in decibels. It indicates the ability to detect a small moving target in ground clutter.
[833] What does "RAG" stand for, and why is the name appropriate?
Range-Azimuth Gating;
"RAG" describes the operation of the circuit itself, gating specified radar operating modes at preselected values with respect to range and azimuth.
[833] What are azimuth strobes used to indicate?
A runway, air route, or approach pattern
[833] How are Range-Azimuth Gating (RAG) circuits programmed?
By means of patch cords and Printed Wire Board (PWB)-mounted Single-Pole Single-Throw (SPST) switches.
[833] What is the maximum distance of landline between ASR and operations sites?
12,000 feet
[833]Which radar videos are remoted to the operations site?
MTI and Normal video
[833] Why does the Memory Control store Control and Status signals in memory?
In the event of a power failure, a temporary power supply provides voltage to keep the memory energized for 10 minutes. This allows the system to be placed on backup power and the system to be re-energized without the need to reset controls.