Subelement B – Transmitting Systems

Question 1

The magnetron is used to:
A. Generate the output signal at the proper operating frequency.
B. Determine the shape and width of the transmitted pulses.
C. Modulate the pulse signal.
D. Determine the pulse repetition rate.

Answer 1

A

Question 2

The purpose of the modulator is to:
A. Transmit the high voltage pulses to the antenna.
B. Provide high voltage pulses of the proper shape and width to the magnetron.
C. Adjust the pulse repetition rate.
D. Tune the Magnetron to the proper frequency.

Answer 2

B

Question 3

Which of the following statements about most modern RADAR transmitter power supplies is false?
A. High voltage supplies may produce voltages in excess of 5,000 volts AC.
B. There are usually separate low voltage and high voltage supplies.
C. Low voltage supplies use switching circuits to deliver multiple voltages.
D. Low voltage supplies may supply both AC and DC voltages.

Answer 3

A

Question 4

The purpose of the Pulse Forming Network is to:
A. Act as a low pass filter.
B. Act as a high pass filter.
C. Produce a pulse of the correct width.
D. Regulate the pulse repetition rate.

Answer 4

C

Question 5

The purpose of the Synchronizer is to:
A. Generate the modulating pulse to the magnetron.
B. Generate a timing signal that establishes the pulse repetition rate.
C. Insure that the TR tube conducts at the proper time.
D. Control the pulse width.

Answer 5

B

Question 6

Which of the following is not part of the transmitting system?
A. Magnetron.
B. Modulator.
C. Pulse Forming Network.
D. Klystron.

Answer 6

D

Question 7

High voltage is applied to what element of the magnetron?
A. The waveguide.
B. The anode.
C. The plate cap.
D. The cathode.

Answer 7

D

Question 8

The characteristic of the magnetron output pulse that relates to accurate range measurement is its:
A. Amplitude.
B. Decay time.
C. Rise time.
D. Duration.

Answer 8

C

Question 9

What device is used as a transmitter in a marine RADAR system?
A. Magnetron.
B. Klystron.
C. Beam-powered pentode.
D. Thyratron.

Answer 9

A

Question 10

The magnetron is:
A. A type of diode that requires an internal magnetic field.
B. A triode that requires an external magnetic field.
C. Used as the local oscillator in the RADAR unit.
D. A type of diode that requires an external magnetic field.

Answer 10

D

Question 11

A negative voltage is commonly applied to the magnetron cathode rather than a positive voltage to the magnetron anode because:
A. The cathode must be made neutral to force electrons into the drift area.
B. A positive voltage would tend to nullify or weaken the magnetic field.
C. The anode can be operated at ground potential for safety reasons.
D. The cavities might not be shock-excited into oscillation by a positive voltage.

Answer 11

C

Question 12

The anode of a magnetron is normally maintained at ground potential:
A. Because it operates more efficiently that way.
B. For safety purposes.
C. Never. It must be highly positive to attract the electrons.
D. Because greater peak-power ratings can be achieved.

Answer 12

B

Question 13

In a solid-state RADAR modulator, the duration of the transmitted pulse is determined by:
A. The thyratron.
B. The magnetron voltage.
C. The pulse forming network.
D. The trigger pulse.

Answer 13

C

Question 14

The modulation frequency of most RADAR systems is between:
A. 60 and 500 Hz.
B. 3000 and 6000 Hz.
C. 1500 and 7500 Hz.
D. 1000 and 3000 Hz.

Answer 14

A

Question 15

A shipboard RADAR uses a PFN driving a magnetron cathode through a step-up transformer. This results in which type of modulation?
A. Frequency modulation.
B. Amplitude modulation.
C. Continuous Wave (CW) modulation.
D. Pulse modulation.

Answer 15

D

Question 16

In a pulse modulated magnetron what device determines the shape and width of the pulse?
A. Pulse Forming Network.
B. Thyratron.
C. LC parallel circuit.
D. Dimensions of the magnetron cavity.

Answer 16

A

Question 17

What device(s) may act as the modulator of a RADAR system?
A. Magnetron.
B. Klystron.
C. Video amplifier.
D. Thyratron or a silicon-controlled rectifier (SCR).

Answer 17

D

Question 18

The purpose of a modulator in the transmitter section of a RADAR is to:
A. Improve bearing resolution.
B. Provide the correct waveform to the transmitter.
C. Prevent sea return.
D. Control magnetron power output.

Answer 18

B

Question 19

The pulse developed by the modulator may have an amplitude greater than the supply voltage. This is possible by:
A. Using a voltage multiplier circuit.
B. Employing a resonant charging choke.
C. Discharging a capacitor through an inductor.
D. Discharging two capacitors in series and combining their charges.

Answer 19

B

Question 20

Pulse transformers and pulse-forming networks are commonly used to shape the microwave energy burst RADAR transmitter. The switching devices most often used in such pulse-forming circuits are:
A. Power MOSFETS and Triacs.
B. Switching transistors.
C. Thyratrons and BJT’s.
D. SCR’s and Thyratrons.

Answer 20

D

Question 21

The purpose of the pulse-forming network is to:
A. Determine the width of the modulating pulses.
B. Determine the pulse repetition rate.
C. Act as a high pass filter.
D. Act as a log pass filter.

Answer 21

A

Question 22

The shape and duration of the high-voltage pulse delivered to the magnetron is established by:
A. An RC network in the keyer stage.
B. The duration of the modulator input trigger.
C. An artificial delay line.
D. The time required to saturate the pulse transformer.

Answer 22

C

Question 23

Pulse-forming networks are usually composed of the following:
A. Series capacitors and shunt inductors.
B. Series inductors and shunt capacitors.
C. Resonant circuit with an inductor and capacitor.
D, None of the above.

Answer 23

B

Question 24

An artificial transmission line is used for:
A. The transmission of RADAR pulses.
B. Testing the RADAR unit, when actual targets are not available.
C. Determining the shape and duration of pulses.
D. Testing the delay time for artificial targets.

Answer 24

C

Question 25

The ferrite material in a circulator is used as a(an): A. Electric switch. B. Saturated reactor. C. Loading element. D. Phase shifter.

Answer 25

D

Question 26

In a circular resonant cavity with flat ends, the E-field and the H-field form with specific relationships. The: A. E-lines are parallel to the top and bottom walls. B. E-lines are perpendicular to the end walls. C. H-lines are perpendicular to the side walls. D. H-lines are circular to the end walls.

Answer 26

B

Question 27

A ferrite circulator is most commonly used in what portion of a RADAR system? A. The antenna. B. The modulator. C. The duplexer. D. The receiver.

Answer 27

C

Question 28

A circulator provides what function in the RF section of a RADAR system? A. It replaces the TR cell and functions as a duplexer. B. It cools the magnetron by forcing a flow of circulating air. C. It permits tests to be made to the thyristors while in use. D. It transmits antenna position to the indicator during operation.

Answer 28

A

Question 29

A directional coupler has an attenuation of -30 db. A measurement of 100 milliwatts at the coupler indicates the power of the line is: A. 10 watts. B. 100 watts. C. 1,000 watts. D. 10,000 watts.

Answer 29

B

Question 30

What is the purpose or function of the RADAR duplexer/circulator? A. An electronic switch that allows the use of one antenna for both transmission and reception. B. A coupling device that is used in the transition from a rectangular waveguide to a circular waveguide. C. A modified length of waveguide used to sample a portion of the transmitted energy for testing purposes. D. A dual section coupling device that allows the use of a magnetron as a transmitter.

Answer 30

A

Question 31

The ATR box: A. Protects the receiver from strong RADAR signals. B. Prevents the received signal from entering the transmitter. C. Turns off the receiver when the transmitter is on. D. All of the above.

Answer 31

B

Question 32

When a pulse RADAR is radiating, which elements in the TR box are energized? A. The TR tube only. B. The ATR tube only. C. Both the TR and ATR tubes. D. Neither the TR nor ATR tubes.

Answer 32

C

Question 33

The TR box: A. Prevents the received signal from entering the transmitter. B. Protects the receiver from the strong RADAR pulses. C. Turns off the receiver when the transmitter is on. D. Protects the receiver from the strong RADAR pulses and mutes the receiver when the transmitter is on.

Answer 33

D

Question 34

What device is located between the magnetron and the mixer and prevents received signals from entering the magnetron? A. The ATR tube. B. The TR tube. C. The RF Attenuator. D. A resonant cavity.

Answer 34

A

Question 35

A keep-alive voltage is applied to: A. The crystal detector. B. The ATR tube. C. The TR tube. D. The magnetron.

Answer 35

C

Question 36

A DC keep-alive potential: A. Is applied to a TR tube to make it more sensitive. B. Partially ionizes the gas in a TR tube, making it very sensitive to transmitter pulses. C. Fully ionizes the gas in a TR tube. D. Is applied to a TR tube to make it more sensitive and partially ionizes the gas in a TR tube.

Answer 36

D

Question 37

What RADAR circuit determines the pulse repetition rate (PRR)? A. Discriminator. B. Timer (synchronizer circuit). C. Artificial transmission line. D. Pulse-rate-indicator circuit.

Answer 37

B

Question 38

The triggering section is also known as the: A. PFN. B. Timer circuit. C. Blocking oscillator. D. Synchronizer.

Answer 38

D

Question 39

Operation of any RADAR system begins in the: A. Triggering section. B. Magnetron. C. AFC. D. PFN.

Answer 39

A

Question 40

The timer circuit: A. Determines the pulse repetition rate (PRR). B. Determines range markers. C. Provides blanking and unblanking signals for the CRT. D. All of the above

Answer 40

D

Question 41

Pulse RADARs require precise timing for their operation. Which type circuit below might best be used to provide these accurate timing pulses? A. Single-swing blocking oscillator. B. AFC controlled sinewave oscillator. C. Non-symmetrical astable multivibrator. D. Triggered flip-flop type multivibrator.

Answer 41

A

Question 42

Unblanking pulses are produced by the timer circuit. Where are they sent? A. IF amplifiers. B. Mixer. C. CRT. D. Discriminator.

Answer 42

C

Question 43

An advantage of resonant charging is that it: A. Eliminates the need for a reverse current diode. B. Guarantees perfectly square output pulses. C. Reduces the high-voltage power supply requirements. D. Maintains a constant magnetron output frequency.

Answer 43

C

Question 44

The characteristics of a field-effect transistor (FET) used in a modern RADAR switching power supply can be compared as follows: A. “On” state compares to a bipolar transistor. “Off” state compares to a 1-Megohm resistor. B. “On” state compares to a pure resistor. “Off” state compares to a mechanical relay. C. “On” state compares to an low resistance inductor. “Off” state compares to a 10-Megohm resistor. D. “On” state compares to a resistor. “Off” state compares to a capacitor.

Answer 44

B

Question 45

A pulse-width modulator in a switching power supply is used to: A. Provide the reference voltage for the regulator. B. Vary the frequency of the switching regulator to control the output voltage. C. Vary the duty cycle of the regulator switch to control the output voltage. D. Compare the reference voltage with the output voltage sample and produce an error voltage.

Answer 45

C

Question 46

In a fixed-frequency switching power supply, the pulse width of the switching circuit will increase when: A. The load impedance decreases. B. The load current decreases. C. The output voltage increases. D. The input voltage increases.

Answer 46

A

Question 47

A major consideration for the use of a switching regulator power supply over a linear regulator is: A. The switching regulator has better regulation. B. The linear regulator does not require a transformer to step down AC line voltages to a usable level. C. The switching regulator can be used in nearly all applications requiring regulated voltage. D. The overall efficiency of a switching regulator is much higher than a linear power supply.

Answer 47

D

Question 48

Which of the following characteristics are true of a power MOSFET used in a RADAR switching supply? A. Low input impedance; failure mode can be gate punch-through. B. High input impedance; failure mode can be gate punch-through. C. High input impedance; failure mode can be thermal runaway. D. Low input impedance; failure mode can be gate breakdown.

Answer 48

B