2009 Element 8 pool
54 / 300 questions need explanations
All explanations are written and maintained by ordinary users like you! Please help us finish the explanations in this pool.
Pulse-forming networks are usually composed of the following:
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Series capacitors and shunt inductors. (18% chose this)
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Series inductors and shunt capacitors. (43% chose this)
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Resonant circuit with an inductor and capacitor. (29% chose this)
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None of the above. (10% chose this)
What component of a RADAR receiver is represented by block 49 in Fig. 8A1?
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Discriminator. (23% chose this)
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IF amplifier. (8% chose this)
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Klystron. (18% chose this)
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Crystal detector (the mixer). (51% chose this)
While the vessel is docked the presentation of the pier is distorted near the center of the PPI with the pier appearing to bend in a concave fashion. This is a primary indication of what?
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The deflection coils need adjusting. (22% chose this)
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The centering magnets at the CRT neck need adjusting. (17% chose this)
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The waveguide compensation delay line needs adjusting. (52% chose this)
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The CRT filaments are weakening. (9% chose this)
A defective crystal in the AFC section will cause:
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No serious problems. (1% chose this)
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Bright flashing pie sections on the PPI. (50% chose this)
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Spiking on the PPI. (13% chose this)
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Vertical spikes that constantly move across the screen. (36% chose this)
RADAR interference on a communications receiver appears as:
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A varying tone. (13% chose this)
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Static. (22% chose this)
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A hissing tone. (11% chose this)
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A steady tone. (54% chose this)
An RF mixer has what purpose in a RADAR system?
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Mixes the CW transmitter output to form pulsed waves. (16% chose this)
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Converts a low-level signal to a different frequency. (53% chose this)
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Prevents microwave oscillations from reaching the antenna. (11% chose this)
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Combines audio tones with RF to produce the RADAR signal. (21% chose this)
To insert RF energy into or extract RF energy from a waveguide, which of the following would not be used?
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Coupling capacitance. (53% chose this)
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Current loop. (9% chose this)
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Aperture window. (17% chose this)
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Voltage probe. (22% chose this)
Which of the following statements about antenna resolvers is correct?
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Most resolvers contain a rotor winding and a delta stator winding. (9% chose this)
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Resolvers consist of a two rotor windings and two stator windings that are 90 degrees apart. (27% chose this)
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The basic resolver contains a rotor winding and two stator windings that are 90 degrees apart. (53% chose this)
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Resolvers consist of a "Y" connected rotor winding and a delta connected stator winding. (11% chose this)
In a RADAR unit, if the crystal mixer becomes defective, replace the:
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Crystal only. (7% chose this)
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The crystal and the ATR tube. (18% chose this)
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The crystal and the TR tube. (56% chose this)
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The crystal and the klystron. (19% chose this)
A circuit card in a RADAR system has just been replaced with a spare card. You notice the voltage level at point E in Fig. 8F12 is negative 4.75 volts when the inputs are all at 5 volts. The problem is:
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The 25 K resistor is open. (11% chose this)
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The 100 K resistor has been mistakenly replaced with a 50 K resistor. (14% chose this)
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The op amp is at the rail voltage. (12% chose this)
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The 50 K resistor has been mistakenly replaced with a 25 K resistor. (64% chose this)
In the circuit contained in Fig. 8F12, there are 5 volts present at points B and C, and there are zero volts present at points A and D. What is the voltage at point E?
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-1.5 Volts. (57% chose this)
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3.75 Volts. (24% chose this)
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23.75 Volts. (7% chose this)
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4.5 Volts. (12% chose this)
In the receive mode, frequency conversion is generally accomplished by a:
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Tunable wave-guide section. (15% chose this)
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Pentagrid converter. (12% chose this)
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Crystal diode. (63% chose this)
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Ferrite device. (10% chose this)
An antenna synchro transmitter is composed of the following:
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Three rotor and two stator windings. (14% chose this)
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Two rotor and three stator windings. (56% chose this)
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Three rotor and three stator windings. (10% chose this)
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A single rotor and 3 stator windings. (19% chose this)
The primary cause of noise in a RADAR receiver can be attributed to:
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Electrical causes. (8% chose this)
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Atmospheric changes. (15% chose this)
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Poor grounding. (17% chose this)
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Thermal noise caused by RADAR receiver components. (60% chose this)
What component of a RADAR receiver is represented by block 48 in Fig. 8A1?
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Klystron (local oscillator). (59% chose this)
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Discriminator. (23% chose this)
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IF amplifier. (9% chose this)
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Crystal detector. (10% chose this)
Which of the following statements is true?
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The front end of the receiver does not provide any amplification to the RADAR signal. (58% chose this)
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The mixer provides a gain of at least 6 db. (6% chose this)
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The I.F. amplifier is always a high gain, narrow bandwidth amplifier. (23% chose this)
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None of the above. (13% chose this)
The klystron local oscillator is constantly kept on frequency by:
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Constant manual adjustments. (2% chose this)
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The Automatic Frequency Control circuit. (62% chose this)
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A feedback loop from the crystal detector. (23% chose this)
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A feedback loop from the TR box. (14% chose this)
When monitoring the gate voltage of a power MOSFET in the switching power supply of a modern RADAR, you would expect to see the gate voltage change from "low" to "high" by how much?
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1 volt to 2 volts. (22% chose this)
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300 microvolts to 700 microvolts. (8% chose this)
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Greater than 2 volts. (63% chose this)
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1.0 volt to 20.0 volts. (6% chose this)
What device(s) could be used as the local oscillator in a RADAR receiver?
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Thyratron (5% chose this)
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Klystron (23% chose this)
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Klystron and a Gunn Diode (63% chose this)
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Gunn diode (8% chose this)
In the circuit shown in Fig. 8A6, which of the following is true?
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With A and B high, Q1 is saturated and Q2 is off. (27% chose this)
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With either A or B low, Q1 is saturated and Q2 is off. (58% chose this)
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With A and B low, Q2 is on and Q4 is off. (7% chose this)
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With either A or B low, Q1 is off and Q2 is on. (7% chose this)
The following is true concerning waveguides:
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Conduction is accomplished by the polarization of electromagnetic and electrostatic fields. (23% chose this)
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Ancillary deflection is employed. (3% chose this)
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The magnetic field is strongest at the center of the waveguide. (14% chose this)
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The magnetic field is strongest at the edges of the waveguide. (61% chose this)
The phantastron circuit is capable of:
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Stabilizing the magnetron. (13% chose this)
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Preventing saturation of the RADAR receiver. (16% chose this)
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Being used to control repeller voltage in the AFC system. (15% chose this)
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Developing a linear ramp voltage when triggered by an external source. (56% chose this)
The modulation frequency of most RADAR systems is between:
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60 and 500 Hz. (63% chose this)
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3000 and 6000 Hz. (9% chose this)
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1500 and 7500 Hz. (13% chose this)
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1000 and 3000 Hz. (16% chose this)
How many sequential memory cells with target returns are required to display the target?
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1 (2% chose this)
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2 (66% chose this)
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4 (21% chose this)
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8 (12% chose this)
In the circuit shown in Fig. 8A4, U5 pins 1 and 4 are high and both are in the reset state. Assume one clock cycle occurs of Clk A followed by one cycle of Clk B. What are the output states of the two D-type flip flops?
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Pin 5 low, Pin 9 low. (18% chose this)
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Pin 5 high, Pin 9 low. (10% chose this)
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Pin 5 low, Pin 9 high. (8% chose this)
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Pin 5 high, Pin 9 high. (64% chose this)
Waveguide theory is based on the principals of:
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Ohm's Law. (14% chose this)
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High standing waves. (7% chose this)
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Skin effect and use of ΒΌ wave stubs. (67% chose this)
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None of the above. (12% chose this)
Which is typical current for a silicon crystal used in a RADAR mixer or detector circuit?
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3 mA (63% chose this)
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15 mA (11% chose this)
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50 mA (20% chose this)
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100 mA (6% chose this)
The usual intermediate frequency of a shipboard RADAR unit is:
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455 kHz. (12% chose this)
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10.7 MHz. (9% chose this)
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30 or 60 MHz. (70% chose this)
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120 MHz. (10% chose this)
The indicated distance from your own vessel to a lighthouse is found to be in error. What circuit would you suspect?
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Range ring oscillator. (68% chose this)
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Video amplifier. (3% chose this)
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STC circuit. (19% chose this)
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FTC circuit. (11% chose this)
How is the variable range marker usually adjusted for accuracy?
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Adjusting the frequency of the VRM oscillator at the maximum range. (17% chose this)
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Adjusting the frequency of the VRM oscillator at the minimum range. (4% chose this)
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Adjusting the readout to match at the median range ring. (8% chose this)
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The minimum and maximum ranges are aligned with the matching fixed range ring. (71% chose this)
Which of the following is not part of the transmitting system?
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Magnetron. (8% chose this)
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Modulator. (8% chose this)
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Pulse Forming Network. (15% chose this)
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Klystron. (69% chose this)
The center of the transmitted lobe from a slotted waveguide array is:
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Several degrees offset from a line perpendicular to the antenna. (68% chose this)
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Perpendicular to the antenna. (30% chose this)
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Maximum at the right hand end. (1% chose this)
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Maximum at the left hand end. (2% chose this)
In a RADAR unit, the mixer uses a:
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Pentagrid converter tube. (5% chose this)
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Field-effect transistor. (11% chose this)
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Silicon crystal or PIN diode. (76% chose this)
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Microwave transistor. (8% chose this)
In a raster-type display, the electron beam is scanned:
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From the center of the display to the outer edges. (12% chose this)
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Horizontally and vertically across the CRT face. (71% chose this)
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In a rotating pattern which follows the antenna position. (11% chose this)
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From one specified X-Y coordinate to the next. (6% chose this)
In a solid-state RADAR modulator, the duration of the transmitted pulse is determined by:
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The thyratron. (13% chose this)
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The magnetron voltage. (8% chose this)
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The pulse forming network. (70% chose this)
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The trigger pulse. (8% chose this)
When comparing a TTL and a CMOS NAND gate:
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Both have active pull-up characteristics. (72% chose this)
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Both have three output states. (4% chose this)
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Both have comparable input power sourcing. (10% chose this)
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Both employ Schmitt diodes for increased speed capabilities. (14% chose this)
A negative voltage is commonly applied to the magnetron cathode rather than a positive voltage to the magnetron anode because:
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The cathode must be made neutral to force electrons into the drift area. (12% chose this)
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A positive voltage would tend to nullify or weaken the magnetic field. (9% chose this)
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The anode can be operated at ground potential for safety reasons. (71% chose this)
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The cavities might not be shock-excited into oscillation by a positive voltage. (8% chose this)
One of the best methods of reducing noise in a RADAR receiver is?
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Changing the frequency. (8% chose this)
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Isolation. (79% chose this)
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Replacing the resonant cavity. (12% chose this)
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Changing the IF strip. (1% chose this)
The anode of a magnetron is normally maintained at ground potential:
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Because it operates more efficiently that way. (9% chose this)
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For safety purposes. (75% chose this)
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Never. It must be highly positive to attract the electrons. (8% chose this)
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Because greater peak-power ratings can be achieved. (8% chose this)
What is the main difference between an analog and a digital receiver?
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Special amplification circuitry. (1% chose this)
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The presence of decision circuitry to distinguish between "on" and "off" signal levels. (80% chose this)
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An AGC stage is not required in a digital receiver. (6% chose this)
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Digital receivers produce no distortion. (14% chose this)
Prior to making "power-on" measurements on a switching power supply, you should be familiar with the supply because of the following:
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You need to know where the filter capacitors are so they can be discharged. (12% chose this)
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If it does not use a line isolation transformer you may destroy the supply with grounded test equipment. (78% chose this)
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It is not possible to cause a component failure by using ungrounded test equipment. (6% chose this)
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So that measurements can be made without referring to the schematic. (4% chose this)
Noise can appear on the LCD as:
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Erratic video and sharp changes in intensity. (76% chose this)
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Black spots on the screen. (11% chose this)
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Changes in bearings. (3% chose this)
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None of the above. (10% chose this)
In a RADAR unit, the mixer uses:
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PIN diodes and silicon crystals. (80% chose this)
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PIN diodes. (6% chose this)
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Boettcher crystals. (2% chose this)
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Silicon crystals. (12% chose this)
How is the signal removed from a waveguide or magnetron?
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With a thin wire called a T-hook. (4% chose this)
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With a thin wire called a J-Hook. (79% chose this)
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With a coaxial connector. (7% chose this)
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With a waveguide flange joint. (10% chose this)
At microwave frequencies, waveguides are used instead of conventional coaxial transmission lines because:
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They are smaller and easier to handle. (5% chose this)
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They have considerably less loss. (78% chose this)
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They are lighter since they have hollow centers. (4% chose this)
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Moisture is never a problem with them. (13% chose this)
A rotary joint is used to:
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Couple two waveguides together at right angles. (10% chose this)
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Act as a switch between two waveguide runs. (8% chose this)
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Connect a stationary waveguide to the antenna array. (75% chose this)
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Maintain pressurization at the end of the waveguide. (8% chose this)
Sea return is:
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Sea water that gets into the antenna system. (0% chose this)
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The return echo from a target at sea. (17% chose this)
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The reflection of RADAR signals from nearby waves. (81% chose this)
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None of the above. (3% chose this)
Low or no mixer current could be caused by:
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Local oscillator frequency misadjustment. (8% chose this)
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TR cell failure. (11% chose this)
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Mixer diode degradation. (3% chose this)
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All of the above. (79% chose this)
The basic frequency determining element in a Gunn oscillator is:
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The power supply voltage. (6% chose this)
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The type of semiconductor used. (6% chose this)
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The resonant cavity. (74% chose this)
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The loading of the oscillator by the mixer. (14% chose this)
A basic sample-and-hold circuit contains:
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An analog switch and an amplifier. (3% chose this)
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An analog switch, a capacitor, and an amplifier. (13% chose this)
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An analog multiplexer and a capacitor. (3% chose this)
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An analog switch, a capacitor, amplifiers and input and output buffers. (80% chose this)
The term DRAM stands for:
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Digital refresh access memory. (4% chose this)
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Digital recording access memory. (6% chose this)
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Dynamic random access memory. (91% chose this)
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Digital response area motion. (0% chose this)
Silicon crystals:
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Are very sensitive to static electric charges. (11% chose this)
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Should be wrapped in lead foil for storage. (3% chose this)
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Tolerate very low currents. (2% chose this)
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All of these. (85% chose this)
Blocking oscillators operate on the formula of:
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T = R x C. (79% chose this)
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I = E/R. (4% chose this)
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By using the receiver's AGC. (9% chose this)
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None of the above are correct. (9% chose this)
What is the most common type of RADAR antenna used aboard commercial maritime vessels?
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Parabolic. (5% chose this)
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Truncated parabolic. (3% chose this)
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Slotted waveguide array. (90% chose this)
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Multi-element Yagi array. (2% chose this)
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