A Student Project
This application was designed & built by:
Alexander Boest-Petersen Christina Elmegaard-Fessel Kristoffer Knudsen Horst Marcia Trillo


(You may want to refer to NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas for a review of standing waves before going further.) Measurements of standing waves can indicate the approximate operating frequency, the presence of defective transmission-line sections, and the condition of the antenna. Standing waves present on transmission lines and waveguides indicate an impedance mismatch between a transmitter or receiver and its antenna. When this condition occurs, the transfer of energy between these units becomes inefficient. Reflection of energy at the load end of a transmission line results in a wave that travels toward the generator end. This reflected wave varies continuously in phase in much the same way that the incident wave varies in phase. At certain points, a half wavelength apart, the two waves are exactly in phase; the resultant voltage is at maximum. At points a quarter wavelength from the maximums, the two waves are in opposition and voltage nodes (null points) are produced. The ratio of maximum-to-minimum voltage at such points is called the VOLTAGE STANDING WAVE RATIO (vswr). The ratio of maximum-to-minimum current along a transmission line is the same as the vswr. A high vswr (1.5 to 1 or higher) indicates that the characteristic impedance of a transmission line differs greatly from the terminating impedance; a low vswr (1 to 1 is best) indicates a good impedance match between the transmission line characteristic impedance and the terminating impedance.
For radar applications, a low vswr is desired for the following reasons: (1) Reflections in the transmission line cause improper transmitter operation and can result in faulty pulsing (this effect is most pronounced when the line is long, as compared with a wavelength of the transmitted energy); (2) arc-over may occur at the maximum voltage points; and (3) hot spots can occur in the transmission line and cause mechanical breakdown. Since transmission lines for radar equipment are normally coaxial cables or waveguides, slotted lines or directional couplers must be used for standing-wave measurements.
Q10. Receiver bandwidth is defined as those frequencies spread between what two points of the receiver response curve?
Q11. The end of the usefulness of a tr tube is indicated by an increase in what quantity?
When you think of radar equipment with its complex electronic circuitry and other sophisticated equipment, you may forget that the entire radar relies on other systems. These other systems are referred to as SUPPORT SYSTEMS and are not normally thought of as part of the radar. These support systems
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include ELECTRICAL POWER, DRY-AIR, and LIQUID-COOLING SYSTEMS. Without these support systems, radars could not function. Therefore, you must be aware of these support systems and understand their relationship to your radar equipment.
Let us now look at a typical ship's power distribution system. The power system on your ship or aircraft is probably similar in many ways. We will briefly discuss an overall power distribution system and the areas that are closely related to radar equipment.
Most ac power distribution systems in naval vessels are 440-volt, 60-hertz, 3-phase, 3-wire, ungrounded systems. The ac power distribution system consists of the power source, equipment to distribute the power, and the equipment which uses the power. A partial distribution chart is shown in figure 4-11.
The power source can be the ship service turbine generator or the emergency diesel generator. Power is normally distributed through the ship service distribution switchboards and power panels. Some large ships also use load centers (not shown) that function as remote switchboards.
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Power is used by any equipment that requires electrical power for its operation (lights, motors, director power drives, radar equipment, weapon direction equipment, computers, etc.). The maintenance of the ship service generators, the emergency generators, and distribution switchboards is the responsibility of the ship's engineers (machinist's mates, electrician's mates, enginemen, etc.).
If power from the ship service distribution system is interrupted, the emergency power distribution system is activated. The emergency system supplies an immediate and automatic source of electrical power to selected loads that are vital to the safety and defense of the ship. This system includes one or more emergency diesel generators and switchboards. The emergency generator is started automatically when a sensor detects the loss of normal power.
Bus transfer equipment is installed on switchboards, at load centers, on power panels, and on loads that are fed by both normal and alternate and/or emergency feeders (figure 4-11). Either the normal or alternate source of the ship's service power can be selected. Emergency power from the emergency distribution system can be used if an emergency feeder is also provided.
Automatic bus transfer (ABT) equipment is used to provide power to vital loads, while nonvital loads can be fed through manual bus transfer (MBT) equipment. For example, the interior communications (IC) switchboard is fed through an ABT in which the alternate input is from the emergency switchboard. A search radar might be fed through an MBT.
Many other supply voltages are used in radar systems and subsystems. They are usually used as reference voltages for specific functions. When you are missing a power input to your equipment, work backwards from the load to the source. Usually, the power panels and bus transfer units that feed the equipment are located nearby, possibly in the same space or in a passageway.
Keep in mind that technicians have corrected many suspected casualties merely by restoring a minor power input or signal reference, sometimes after hours of troubleshooting.
Q12. Most shipboard distribution systems use ac power that has what number of phases?
Q13. How is emergency power applied when normal power is lost?
Q14. What device is used to switch power from the normal source to an alternate source for nonvital users?
Q15. What procedure should you use when a power input to your equipment is missing?
Some radars depend on inputs of dry air for proper operation. Radar dry air is normally supplied by the ship's central dry-air system. This system produces high-pressure (hp) air and low-pressure (lp) dry air for distribution to user equipment, such as a search or a fire control radar.
The electronics dry-air branch is fed from the vital service lp air main through the Type II (desiccant) or Type III (combination refrigerant and desiccant) dehydrators, as shown in figure 4-12. The purpose of
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the electronics dry-air branch is to provide several electronic equipments with air that is dry enough for proper operation. Microwave components, such as waveguides, cavities, and power amplifiers, require dry air to prevent arcing and internal corrosion. The electronics dry-air branch must satisfy the dry-air requirements of the electronic user equipment. Dry air of less than the required specifications will degrade equipment performance. It may also incur major repairs, overhaul, or replacement of expensive electronic components.
The dry-air distribution system (figure 4-12) delivers dry air to each air control panel of the user equipment. The air control panels are used to control and regulate the dry-air pressure to that required by the electronic user equipment.
The air control panel (figure 4-13) provides a means of monitoring the dry-air supply to the user equipment. The type of control panel used varies, depending on the outlet pressure and flow rate required.
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The dew point (related to moisture content) and the flow of the lp dry air can be monitored at the air control panel. Also, the dry-air pressure can be monitored at the input to the control panel, at the input to the flowmeter (in which accuracy is calibrated at a certain pressure), and at the output of the control panel. A filter is installed to trap particles that affect proper pressure regulation. A metering valve bypass and a pressure relief valve are provided in case of malfunctions. The metering valve bypass permits manual control of air pressure to the user equipment.
Electronic Equipment Dehydrators.
Dehydrators or compressor-dehydrators are supplied as part of various radars. Many of them were provided prior to installation of properly configured central dry-air systems. These dehydrators are intended for emergency use in the event of the failure of the central dry-air system. In a typical configuration (figure 4-14), the outlet air from the local dehydrator is connected between the air control panel outlet and the user equipment or radar by a three-way valve.
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Local dehydrators depend on the ship's lp air for an inlet supply, while the local compressor- dehydrators can operate independently of the ship's air supply. Some units of electronic equipment that have local dehydrator units are pressure interlocked within the dehydrator unit. When the outlet air pressure is below a set value, the interlock prevents the equipment from going to a full OPERATE condition. When the central dry-air system is used, the pressure interlock is bypassed.
Some radars provide a tank of nitrogen as an emergency source that can be connected in place of dry air. Special safety precautions must be taken when you handle compressed gases because of the possibility of explosion. Nitrogen does not support life; when released in a confined space, it can cause asphyxiation.
Q16. What is the normal source of dry air for a radar system?
Q17. What is the major difference between the electronics dry-air branch and the vital service lp air main?
Q18. What is the air control panel designed to control?
Radar equipment, particularly the high-power transmitters, generate large amounts of heat. This heat must be dissipated to prevent damage to the equipment and to prevent erratic circuit operation. Most radar equipment rooms have high-capacity air-conditioning systems to control the ambient room temperature;
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however, equipment cabinets must have additional cooling to control the internal temperature. In the case of transmitters (and other high-voltage circuits), individual components may require cooling.
Cabinets that generate relatively small amounts of heat may only require a system of fans or blowers to maintain constant air circulation. In some cases the air is circulated through a liquid-cooled heat exchanger located inside the cabinet.
Most low-power amplifier tubes are air cooled; most high-power tubes, such as klystrons, crossed- field amplifiers, and magnetrons, are liquid cooled.
The main source of power and heat in a power amplifier package is the high-voltage power supply. Part of the power produced by the power amplifier is transmitted in the form of rf energy; the remainder of the power eventually converts to heat, and cooling is required to dissipate the heat.
Radars that use blowers for cooling will usually have an airflow sensing switch. If the blower fails, the switch will open and remove power from appropriate power supplies. Radars employing liquid cooling normally distribute the liquid into a large number of separate paths, because the flow requirements are quite dissimilar. Each of the various paths will have a low flow interlock. If one of the liquid cooling paths becomes restricted, the low flow interlock switch will open and remove power from the radar.
Liquid cooling systems also include pressure gauges and switches, temperature gauges, and overtemperature switches. Many systems have pressure or flow regulators. Some systems include audio and/or visual alarms that energize before damage actually occurs. In some cases this allows the problem to be corrected without turning off the equipment.
Figure 4-15 illustrates a typical transmitter cooling system showing the many protective devices.
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Distilled water is one of the best mediums for cooling high-power components, and, in many cases, the only medium that may be used.
For a distilled-water-cooling system to operate satisfactorily, the temperature, quantity, purity, flow, and pressure of the water must be controlled. This control is provided by various valves, regulators, sensors, meters, and instruments that measure the necessary characteristics and provide the required regulation.
Liquid-cooling systems consist of a sea water or a chilled (fresh) water section that cools the distilled water circulating through the electronic equipment. The main components of cooling systems are piping, valves, regulators, heat exchangers, strainers, circulating pumps, expansion tanks, gages, and demineralizers. Other specialized components are sometimes necessary to monitor cooling water to the electronic equipment.
A typical liquid-cooling system is composed of a PRIMARY LOOP and a SECONDARY LOOP (figure 4-16). The primary loop provides the initial source of cooling water and the secondary loop transfers the heat load from the electronic equipment to the primary loop. The source of cooling water for the primary loop is either sea water from a sea water supply or chilled water from the ship's air- conditioning plant. The cooling water used in the secondary loop is distilled water. Ultrapure systems are maintained by a demineralizer and use double-distilled water obtained through the Navy Supply System.
Additional information about liquid cooling systems can be found in Basic Liquid Cooling Systems for Shipboard Electronic Equipment Technician's Handbook, NAVSEA 0948-LP-122-8010.
Q19. What type of cooling is used to control ambient room temperature?
Q20. A typical liquid-cooling system is composed of what loops?
Q21. What loop of a cooling system is often supplied by sea water?
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Many safety and health hazards are involved with operating and maintaining high-power radars. These hazards result from high levels of rf radiation, X-ray emissions, the necessity of working aloft, and the generation of extremely high voltages.
Navy professionals are very safety conscious and, as a result, the number of accidents that occur on the job is small. Most of the safety precautions applicable to radar are published in radar technical manuals. Many of the safety regulations included in technical manuals are the result of actual experiences. Therefore, you should give them careful thought and strict observance.
Radar peak power may reach a million watts or more. Rf radiation hazards exist in the vicinity of radar transmitting antennas. These hazards are present not only in front of an antenna but also to the sides and sometimes even behind it because of spillover and reflection. At some frequencies, exposure to excessive levels of radiation will not produce a sufficient sensation of pain or discomfort to warn you of injury. If you suspect any injury, see your ship's doctor or corpsman. Be sure to acquaint yourself with the actual radiation hazard zones of the radars on your ship.
Personnel should observe the following precautions to ensure that persons are not exposed to harmful rf radiation:
• Visual inspection of feedhorns, open ends of waveguides, and any other opening that emits rf energy should not be made unless the equipment is properly secured and tagged for that purpose.
• Operating and maintenance personnel should observe all rf radiation hazard signs posted in the operating area.
• All personnel should observe rf radiation hazard (radhaz) warning signs (figure 4-17) that point out the existence of rf radiation hazards in a specific location or area. (You may encounter other types of rf radiation hazard signs, depending on the situation.)
• Ensure that radiation hazard warning signs are available and posted.
• Ensure that those radar antennas that normally rotate are rotated continuously while radiating or are trained to a known safe bearing.
• Ensure that those antennas that do not normally rotate are pointed away from inhabited areas (ships, piers, and the like) while radiating.
• Dummy loads should be employed where applicable in transmitting equipment during testing or checkout.
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X rays may be produced by the high-voltage electronic equipment in radars. X rays can penetrate human tissue and cause damage of a temporary or permanent nature. Unless the dosage is extremely high, no ill effects will be noticeable for days, weeks, or even years after the exposure.
The sources of these X rays are usually confined to magnetrons, klystrons, and cathode-ray tubes. Personnel should not linger near any of these types of equipments when the equipment covers have been removed. Klystrons, magnetrons, rectifiers, or other tubes that employ an excitation of 15,000 volts or more may emit X rays out to a few feet; thus, unshielded personnel standing or working close to the tubes will be endangered.
When performing maintenance on X-ray emitting devices, you should take the following precautions:
• Observe all warning signs (figure 4-18) on the equipment and all written precautions in the equipment technical manuals.
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• Unless called for in the technical manual, do not bypass interlocks to permit the servicing of operating equipment with the X-ray shield removed.
• Be sure to replace all protective X-ray shielding when servicing is complete.
This chapter has presented information on radar maintenance procedures. The information that follows summarizes the important points of this chapter.
Transmitter PERFORMANCE CHECKS are essential for you to maintain an efficient radar system. The transmitter output must be monitored closely for both frequency and power.
Transmitter energy is distributed symmetrically over a band of frequencies known as the SPECTRUM.
A SPECTRUM CURVE for a transmitter in good condition is shown in the illustration.
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The SPECTRUM ANALYZER and the ECHO BOX are two instruments used to check transmitter performance.
One of the more important measurements that can be performed with the echo box is RING TIME. Ring time gives a relative indication of both transmitter output power and receiver sensitivity.
Transmitter OUTPUT POWER MEASUREMENTS are a good indication of overall transmitter operation. POWER MEASUREMENTS are usually of average power read in dBm. The average power dBm reading must be converted to watts and the peak power calculated. The formula for peak power is:
RECEIVER PERFORMANCE CHECKS determine receiver sensitivity, tr recovery time, and receiver bandwidth.
You usually measure receiver sensitivity by measuring the MINIMUM DISCERNIBLE SIGNAL (mds) using the pulse method.
TR RECOVERY time is the time required for the tr tube to DEIONIZE after each transmitted pulse. You should keep a graph of tr recovery time to determine when the tr tube should be replaced. If not replaced in a timely manner, a weak tr tube will allow damage to the radar receiver.
Few radars can function without SUPPORT SYSTEMS. These support systems include ELECTRICAL POWER, DRY-AIR, and LIQUID-COOLING SYSTEMS.
The radar technician should learn the source and distribution routes for NORMAL and EMERGENCY POWER for the radar.
The DRY AIR needed for electronic equipment can be supplied by the ship's electronics dry-air system through an air control panel or from local dehydrators.
Radar transmitters generate large amounts of heat. Most of this heat is dissipated by a combination of AIR CONDITIONING, CABINET AIR BLOWERS, and a DISTILLED-WATER COOLING system.
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Personnel working on radars should always be aware of the hazards of RF RADIATION and X-RAY EMISSION.
All posted SAFETY PRECAUTIONS should be strictly observed.
ANSWERS TO QUESTIONS Q1. THROUGH Q21.
A1. Frequency distribution.
A2. In the center.
A3. Symmetrical above and below the carrier frequency.
A4. Power and frequency.
A5. Average power, pulse width, and prt.
A6. 1 milliwatt.
A7. Transmitter power loss.
A8. Minimum discernible signal (mds).
A9. Attenuations of the directional coupler and the connecting cable.
A10. Half-power points.
A11. Recovery time.
A12. Three.
A13. Automatically.
A14. Manual bus transfer (MBT) unit.
A15. Work backwards from the load to the source.
A16. Ship's central dry-air system.
A17. Degree of dehydration.
A18. Pressure.
A19. Air conditioning.
A20. Primary and secondary.
A21. The primary loop.
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A-SCOPE—A radar display on which slant range is shown as the distance along a horizontal trace.
ACQUISITION—Operational phase of a fire- control or track radar during which the radar system searches a small volume of space in a prearranged pattern.
AIR-CONTROL PANEL—Panel that monitors the dry-air input at each user equipment.
ALTITUDE—Vertical distance of an aircraft or object above a given reference, such as ground or sea level.
AMBIGUOUS RETURNS—Echoes that exceed the prt of a radar and appear at incorrect ranges.
AMPLITRON—See Crossed-Field Amplifier.
ANTENNA SYSTEM—Routes rf energy from the transmitter, radiates the energy into space, receives echoes, and routes the echoes to the receiver.
ANTIJAMMING CIRCUIT—Electronic circuit used to minimize the effects of enemy countermeasures, thereby permitting radar echoes to be visible on the indicator.
ANTITRANSMIT-RECEIVE TUBE (atr)—Tube that isolates the transmitter from the antenna and receiver. Used in conjunction with tr tube.
ARTIFICIAL TRANSMISSION LINE—An LC network that is designed to simulate characteristics of a transmission line.
ASYMMETRICAL MULTIVIBRATOR—Multivibrator that generates rectangular waves.
AUTOMATIC GAIN CONTROL—Circuit used to vary radar receiver gain for best reception of signals that have widely varying amplitudes.
AVERAGE POWER—Output power of a transmitter as measured from the start of one pulse to the start of the next pulse.
AZIMUTH—Angular measurement in the horizontal plane in a clockwise direction.
BALANCED MIXER—Waveguide arrangement that resembles a T and uses crystals for coupling the output to a balanced transformer.
BEAM—See Lobe.
BEARING RESOLUTION—Ability of a radar to distinguish between targets that are close together in bearing.
BEAT FREQUENCIES—Difference and sum frequencies which result from combining two different frequencies.
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BLIP—See Pip.
BLOCKING—A condition in an amplifier, caused by overdriving one or more stages, in which the amplifier is insensitive to small signals immediately after reception of a large signal.
BROADSIDE ARRAY—An antenna array in which the direction of maximum radiation is perpendicular to the plane of the array.
BUFFER AMPLIFIER STAGE—Amplifier stage that isolates one circuit from another.
CARRIER FREQUENCY—The frequency of an unmodulated transmitter output. CARRIER-CONTROLLED APPROACH—Shipboard radar system used to guide aircraft to safe
landings in poor visibility conditions.
CLUTTER—Confusing, unwanted echoes that interfere with the observation of desired signals on a radar indicator.
COHERENCE—A definite phase relationship between two energy waves, such as transmitted frequency and reference frequency.
COHERENT OSCILLATOR—In cw radar this oscillator supplies phase references to provide coherent video from target returns.
CONICAL SCANNING—Scanning in which the movement of the beam describes a cone, the axis of which coincides with that of the reflector.
CONTACT—In radar, an object that reflects rf energy; target. CORNER REFLECTOR—Two flat reflectors that meet at an angle and are normally fed by a half-wave
radiator.
CROSSED-FIELD AMPLIFIER—High-power electron tube that converts dc to microwave power by a combination of crossed electric and magnetic fields.
CYLINDRICAL PARABOLIC REFLECTOR—A parabolically shaped reflector that resembles part of a cylinder.
DEFLECTION COILS—In a cathode-ray tube, coils used to bend an electron beam a desired amount.
DEIONIZATION TIME—In a spark gap, the time required for ionized gas to return to its neutral state after the spark is removed.
DESIGNATION—Operational phase of a fire- control or track radar during which the radar is directed to the general direction of a desired target.
DIFFERENCE FREQUENCY—See Beat Frequency. DIODE DETECTOR—A demodulator that uses one or more diodes to provide a rectified output with an
average value that is proportional to the original modulation.
DIRECTIONAL ANTENNA—An antenna that radiates most effectively in only one direction.
DIRECTIVITY—Ability of an antenna to radiate or receive more energy in some directions than in others. The degree of sharpness of the antenna beam.
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DISCRIMINATOR—A circuit in which amplitude variations are derived in response to phase or frequency variations.
DISTILLED WATER—Water that has been purified through a process of evaporation and condensation.
DOPPLER EFFECT—In radar, the change in frequency of a received signal caused by the relative motion between the radar and the target.
DOPPLER FREQUENCY—Difference between transmitted and reflected frequencies; caused by the Doppler effect.
DOUBLE-MODING—In a transmitter output tube, the abrupt and random change from one frequency to another.
DRY-AIR SYSTEM—Provides dehumidified air for electronic equipment that is moisture critical.
DUCTING—Trapping of an rf wave between two layers of the earth's atmosphere or between an atmospheric layer and the earth.
DUPLEXER—A radar device that switches the antenna from the transmitter to the receiver and vice versa.
DUTY CYCLE—In a transmitter, ratio of time on to time off.
ECHO—The rf signal reflected back from a radar target.
ECHO BOX—A resonant cavity device that is used to check the overall performance of a radar system. It receives a portion of the transmitted pulse and retransmits it back to the receiver as a slowly decaying transient.
ELECTRICAL POWER SYSTEM—Provides the necessary input power.
ELECTRONIC COUNTER-COUNTERMEASURES (ECCM) CIRCUITS—See Antijamming Circuits.
ELECTRONIC EQUIPMENT DEHYDRATOR—Provides alternate dry-air input in the event of failure of the central dry-air system. May include a compressor.
ELECTRONIC FREQUENCY COUNTER—An instrument that counts the number of cycles (pulses) occurring during a precise time interval.
ELECTRONIC SCANNING—Scanning in which the axis of the beam is moved, relative to the antenna axis, in a desired pattern.
ELECTRONICS DRY-AIR BRANCH—A common line for providing dry air to various electronic equipment, such as search radar, fire-control radar, and repeaters.
ELEVATION ANGLE—The angle between the horizontal plane and the line of sight.
EMERGENCY POWER—Temporary source of limited electrical power used upon the loss of the normal power source.
EXTERNALLY SYNCHRONIZED RADAR—Radar system in which timing pulses are generated by a master oscillator external to the transmitter.
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FAST-TIME-CONSTANT CIRCUIT—Differentiator circuit in the first video amplifier that allows only the leading edges of target returns, no matter how small or large, to be used.
FEEDBACK—The return of a portion of the output of a circuit to its input.
FEEDHORN—A horn radiator used to feed a reflector.
FIRST DETECTOR—See Mixer.
FREQUENCY COMPENSATION NETWORK—Circuit modification used to improve or broaden the linearity of its frequency response.
FREQUENCY SCANNING—Varying the output frequency to achieve electronic scanning. FREQUENCY SPECTRUM—In a radar, the entire range of frequencies contained in an rf pulse or
signal.
FREQUENCY SYNTHESIZER—A bank of oscillators in which the outputs can be mixed in various combinations to produce a wide range of frequencies.
GAIN—Any increase in the strength of a signal.
GATED AGC—Circuit that permits automatic gain control to function only during short time intervals.
GLOW DISCHARGE—Discharge of electricity through a gas in an electron tube.
GROUND CLUTTER—Unwanted echoes from surrounding land masses that appear on a radar indicator.
GROUND RANGE—The distance on the surface of the earth between a radar and its target. Equal to slant range only if both radar and target are at the same altitude.
GROUND-CONTROLLED APPROACH—Radar system used to guide aircraft to safe landings in poor visibility conditions.
GUIDANCE RADAR—System which provides information that is used to guide a missile to a target.
HALF-POWER POINT—A point on a waveform or radar beam that corresponds to half the power of the maximum power point.
HARD-TUBE MODULATOR—A high-vacuum electron tube modulator that uses a driver for pulse forming.
HEIGHT-FINDING RADAR—Radar that provides target altitude, range, and bearing data.
HITS PER SCAN—The number of times an rf beam strikes a target per antenna revolution.
HORIZONTAL PLANE—Imaginary plane that is tangent (or parallel) to the earth's surface at a given location.
HORN ANTENNA—See Horn Radiator.
HORN RADIATOR—A tubular or rectangular microwave antenna that is tapered and is widest at the open end.
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HYBRID RING—A circular waveguide arrangement with four branches. When properly terminated, energy is transferred from any one branch into any two of the remaining three branches.
HYBRID MIXER—See Balanced Mixer.
IF AMPLIFIER—Usually a narrow-bandwidth IF amplifier that is tuned to one of the output frequencies produced by the mixer.
INDEX OF REFRACTION—The degree of bending of an rf wave when passing from one medium to another.
INDICATOR—Equipment that provides a visual presentation of target position information.
INSTANTANEOUS AUTOMATIC GAIN CONTROL (IAGC)—Circuit that can vary the gain of the radar receiver with each input pulse to maintain the output peak amplitude nearly constant.
INTERMEDIATE FREQUENCY (IF)—A lower frequency to which an rf echo is converted for ease of amplification.
KEEP-ALIVE CURRENT—See Keep-Alive Voltage.
KEEP-ALIVE VOLTAGE—Dc voltage applied to a tr gap electrode to produce a glow discharge that allows the tube to ionize faster when the transmitter fires.
KEYED-OSCILLATOR TRANSMITTER—A transmitter in which one stage is used to produce the rf pulse.
KEYER—See Synchronizer.
KLYSTRON POWER AMPLIFIER—Multicavity microwave electron tube that uses velocity modulation.
LIN-LOG AMPLIFIER—Amplifier in which the response is linear for weak signals and logarithmic for large signals.
LINE OF SIGHT—Straight line from a radar antenna to a target.
LINE-PULSING MODULATOR—Circuit that stores energy and forms pulses in the same circuit element, usually the pulse-forming network (pfn).
LIQUID-COOLING SYSTEM—Source of cooling for high-heat producing equipments, such as microwave components, radar repeaters, and transmitters.
LOBE—An area of greater signal strength in the transmission pattern of an antenna.
LOGARITHMIC RECEIVER—Receiver that uses a linear logarithmic amplifier (lin-log) instead of a normal linear amplifier.
LOW-NOISE AMPLIFIER—See Preamplifier.
MAGIC T—See Balanced Mixer.
MAGNETRON OSCILLATOR—Electron tube that provides a high power output. Theory of operation is based on interaction of electrons with the crossed electric and magnetic fields in a resonant cavity.
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MASTER OSCILLATOR—In a transmitter, the oscillator that establishes the carrier frequency of the output.
MECHANICAL SCANNING—The reflector, its feed source, or the entire antenna is moved in a desired pattern.
MINIMUM DISCERNIBLE SIGNAL (MDS)—The weakest signal that produces a usable signal at the output of a receiver. The weaker the signal, the more sensitive the receiver.
MIXER—In radar, a circuit that combines the received rf signal with a local-oscillator signal to effectively convert the received signal to a lower IF frequency signal.
MODE SHIFTING—In a magnetron, shifting from one mode to another during a pulse.
MODE SKIPPING—Rather than firing on each successive pulse as desired, the magnetron fires randomly.
MODES—Operational phases (of a radar). MODULATOR SWITCHING DEVICE—Controls the on (discharge) and off (charge) time of the
modulator.

MONOPULSE (SIMULTANEOUS) LOBING—Radar receiving method using two or more (usually four) partially overlapping lobes. Sum and difference channels locate the target with respect to the axis of the antenna.
MONOPULSE RADAR—A radar that gets the range, bearing, and elevation position data of a target from a single pulse.
MONOPULSE RECEIVER—See Monopulse Lobing.
MOISTURE LAPSE—Abnormal variation of moisture content at different altitudes because of high moisture located just above large bodies of water.
MOVING TARGET INDICATOR—A device that limits the display of radar information to moving targets.
NAUTICAL MILE—The length of a minute of arc of a great circle of the earth (6,076 ft.) NAUTICAL RADAR MILE—See Radar Mile.
NOISE—In radar, erratic or random deflection or intensity of the indicator sweep that tends to mask small echo signals.
NOISE FIGURE—The ratio of output noise to input noise in a receiver.
NUTATING—Moving an antenna feed point in a conical pattern so that the polarization of the beam does not change.
OMNIDIRECTIONAL ANTENNA—An antenna that radiates equally in all directions (nondirectional). ORANGE-PEEL PARABOLOID—A section of a complete circular paraboloid that is narrow in the
horizontal plane and wide in the vertical plane.
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PARABOLIC REFLECTOR—An antenna reflector in the shape of a parabola. It converts spherical wavefronts from the radiating element into plane wavefronts.
PARALLEL-CONNECTED DUPLEXER—Configuration in which the tr spark gap is connected across the two legs of the transmission line one-quarter wavelength from the Tjunction.
PARASITIC ARRAY—An antenna array containing one or more elements not connected to the transmission line.
PEAK POWER—Maximum power of the rf pulse from a radar transmitter.
PERSISTANCE—The length of time a phosphor dot glows on a crt before disappearing.
PHANTASTRON—A variable-length sawtooth generator used to produce a sweep on an A-scope.
PIP (BLIP)—On a crt display, a spot of light or a base-line irregularity representing the radar echo. PLANE WAVEFRONTS—Waves of energy that are flat, parallel planes and perpendicular to the
direction of propagation.
PLANNED-POSITION INDICATOR—A radar display in which range is indicated by the distance of a bright spot or pip from the center of the screen and the bearing is indicated by the radial angle of the spot.
POWER GAIN—In an antenna, the ratio of its radiated power to that of a reference.
POWER-AMPLIFIER (CHAIN) TRANSMITTER—Transmitter that uses a series of power amplifiers to create a high level of power.
PREAMPLIFIER (PREAMP)—An amplifier that raises the output of a low-level source for further processing without appreciable degradation of the signal-to-noise ratio.
PRIMARY LOOP—In a cooling system, the primary source of cooling for the distilled water.
PROBE COUPLER—A resonant conductor placed in a waveguide or cavity to insert or extract energy.
PULSE WIDTH—Duration of time between the leading and trailing edges of a pulse.
PULSE-FORMING NETWORK (PFN)—An LC network that alternately stores and releases energy in an approximately rectangular wave.
PULSE-REPETITION RATE (PRR)—Average number of pulses per unit of time; pulse rate. PULSE-REPETITION FREQUENCY (PRF)—The rate at which pulses are transmitted, given in hertz
or pulses per second; reciprocal of pulse-repetition time.
PULSE-REPETITION TIME (PRT)—Interval between the start of one pulse and the start of the next pulse; reciprocal of pulse-repetition frequency.
RADAR—An acronym for RAdio Detecting And Ranging.
RADAR ALTIMETER—Airborne radar that measures the distance of the aircraft above the ground.
RADAR BEAM—The space in front of a radar antenna where a target can be effectively detected or tracked.
AI-8
RADAR DISTRIBUTION SWITCHBOARD—An electrical switching panel used to connect inputs from any of several radars to repeaters.
RADAR MILE—Time interval (12.36 microseconds) for rf energy to travel out from a radar to a target and back to the radar; radar nautical mile.
RADAR TEST SET—Combination of several test circuits and equipment used to test various characteristics of a radar.
RANGE—The length of a straight line between a radar set and a target.
RANGE-HEIGHT INDICATOR—A radar display on which slant range is shown along the X axis and height along the Y axis.
RANGE-GATE—A movable gate used to select radar echoes from a very short-range interval.
RANGE MARKER—A movable vertical pulse on an A-scope or ring on a ppi scope used to measure the range of an echo or to calibrate the range scale.
RANGE RESOLUTION—Ability of a radar to distinguish between targets that are close together.
RANGE STEP—On an A-scope sweep, vertical displacement used to measure the range of an echo.
RECEIVER—In radar, a unit that converts rf echoes to video and/or audio signals.
RECEIVER SENSITIVITY—The degree to which a receiver can usefully detect a weak signal; the lower limit of useful signal input to the receiver.
RECOVERY TIME—In a radar, the time interval between the end of the transmitted pulse and the time when echo signals are no longer attenuated by the tr gap.
REFLECTING OBJECT—In radar, an air or surface contact that provides an echo.
REFLEX KLYSTRON—A microwave oscillator that is tuned by changing the repeller voltage.
REFRACTION—The bending of rf waves as the waves pass through mediums of different density.
REFRACTIVE INDEX—In a wave-transmission medium, the ratio between the phase velocity in free space and in the medium.
REGENERATION—See Feedback.
RELATIVE BEARING—Bearing of target measured in a clockwise direction from "dead ahead" of a ship or plane.
RESONANCE CHAMBER—See Echo Box.
RETURN—The rf signal reflected back from a radar target; echo.
RF RADIATION HAZARD—Health hazard caused by exposure to electromagnetic radiation or high- energy particles (ions). Abbreviated RADHAZ.
RING TIME—In radar, the time during which the output of an echo box remains above a specified level.
RINGING—Rf oscillations caused by shock excitation of a resonant circuit (cavity).
AI-9
SCANNING—Systematic movement of a radar beam to cover a definite pattern or area in space.
SEA CLUTTER—Unwanted echoes from the irregular surface of the sea that appear on a radar indicator.
SEARCH RADAR SYSTEM—Early-warning device that searches a fixed volume of space.
SECOND DETECTOR DEMODULATOR—The part of the receiver that separates the audio or video component from the modulated intermediate frequency.
SECOND-SWEEP ECHOES—See Ambiguous Returns.
SECONDARY LOOP—In a cooling system, the loop that transfers the heat from the heat source (electronic equipment) to the primary loop; usually distilled water.
SELF-SYNCHRONIZED RADAR—A type of radar in which the timing pulses are generated within the transmitter.
SENSITIVITY TIME CONTROL (STC)—A circuit that varies the gain of a receiver as a function of time.
SERIES-CONNECTED DUPLEXER—Configuration in which the tr spark gap is connected in series in one leg of the transmission line one-half wavelength away from the T- junction.
SHADOW—A dead spot (minimum radiation) caused by the physical obstruction of transmitted waves by a feed horn.
SINGLE-ENDED MIXER—See Unbalanced Crystal Mixer.
SINGLE, STATIONARY-LOBE SCANNING SYSTEM—Antenna (with a single, stationary beam) that is rotated to obtain 360-degree coverage.
SLANT RANGE—See Range.
SPECTRUM ANALYZER—A test instrument that provides a visual display of the frequency distribution of a transmitter output.
SPHERICAL WAVEFRONTS—Waves of energy that spread out in concentric circles.
STABILITY—In a magnetron, the ability to maintain normal operating characteristics.
STATUTE MILE—I5,280 ft.
STUB—A short section of transmission line connected in parallel with the main transmission line.
SCINTILLATION—Apparent change in target reflectivity. Motion of the target causes radar pulses to bounce off different parts of the target, such as fuselage and wingtip.
SUPERHETERODYNE RECEIVER—A type of receiver that uses a mixer to convert the rf echo to an IF signal for amplification.
SUPPORT SYSTEM—For a radar, a system that provides an auxiliary input, such as dry air, electrical power, or liquid cooling.
SYMMETRICAL MULTIVIBRATOR—Circuit that generates square waves.
AI-10
SYNCHRONIZER—Circuit that supplies timing signals to other radar components.
TARGET—In radar, a specific object of radar search or detection. TARGET RESOLUTION—The ability of a radar to distinguish between two or more targets that are
close to each other.
THREE-DIMENSIONAL RADAR (3D)—Measures the range, bearing, and altitude of a target. THYRATRON—Gas tube used as a modulator switching device.
TIMER—See Synchronizer.
TR RECOVERY TIME—Time required for a fired tr or atr tube to deionize to a normal level of conductance.
TRACK—Operational phase of a fire-control or track radar during which the radar beam is kept on the target.
TRACK RADAR—Radar that provides continuous range, bearing, and elevation data by keeping the rf beam on the target.
TRANSMIT-RECEIVE TUBE (TR)—Gas-filled rf switch that is used as a duplexer. TRANSMITTER—Equipment that generates, amplifies, and modulates electromagnetic energy.
TRANSMITTER FREQUENCY (CARRIER FREQUENCY)—The frequency of the unmodulated output of a transmitter.
TRAVERSE (BEARING) SIGNAL—In a monopulse radar system, the combination of individual lobe signals that represents target offset direction and amplitude from the antenna axis.
TRIGGER GENERATOR—See Synchronizer.
TRIGGER PULSES—In radar, pulses that are used to initiate specific events.
TRUE BEARING—Angle between a target and true north measured clockwise in the horizontal plane.
TRUE NORTH—Geographic north.
TRUNCATED PARABOLOID—A paraboloid reflector that has been cut away at the top and bottom to increase beam width in the vertical plane.
TWO-DIMENSIONAL RADAR (2D)—Measures the range and bearing to a target. UNBALANCED CRYSTAL MIXER—Circuit consisting of a section of coaxial transmission line one-
half wavelength long that is tuned to the difference (intermediate) frequency between the local oscillator and rf echo signals.
VERTICAL PLANE—Imaginary plane that is perpendicular to the horizontal plane.
VIDEO ENHANCEMENT FEATURES—See Antijamming Circuits. VOLTAGE STANDING WAVE RATIO (VSWR)—In a waveguide, the ratio of the electric field at a
maximum point to that of an adjacent minimum point.
AI-11
WAVEGUIDE DUPLEXER—Consists of tr and atr tubes housed in a resonant cavity attached to a waveguide system.
WAVEMETER—An instrument for measuring the wavelength of an rf wave.
X-RAY EMISSION—Penetrating radiation similar to light, but with shorter wavelength, that can penetrate human tissue.
AII-1
Shipboard Electronics Material Officer, NAVEDTRA 10478-A, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1982.
Basic Electronics, Vol. 1, NAVPERS 10087-C, Bureau of Naval Personnel, Washington, DC.
Aviation Fire Control Technician 3 & 2, NAVEDTRA 10387-B, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1977.
Fire Control Technician M 3, NAVEDTRA 10224, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1981.
Fire Control Technician M 3 & 2, NAVEDTRA 10209-A, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1974.
Aviation Fire Control Technician 3 & 2, NAVEDTRA 10387-B, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1977.
Basic Electronics, Vol. 2, NAVEDTRA 10087-CI, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1979.
Fire Control Technician M 1 & C, NAVPERS 10210, Bureau of Naval Personnel, Washington, D.C.
Fire Control Technician M 3 & 2, NAVEDTRA 10209-A, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1974.
Shipboard Electronics Material Officer, NAVEDTRA 10478-A, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1982.
Basic Electronics, Vol. 2, NAVEDTRA 10087-C1, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1979.
Aviation Fire Control Technician 3 & 2, NAVEDTRA 10387-B, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1977.
AII-2
Fire Control Technician G 3 & 2, NAVEDTRA 10207-B, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1976.
Electronics Technician 3 & 2, Vol. 2, NAVEDTRA 10195-A, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1979.
Aviation Fire Control Technician 3 & 2, NAVEDTRA 10387-B, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1977.
Fire Control Technician M 3, NAVEDTRA 10224, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1981.
Basic Electronics, Vol 2, NAVEDTRA 10087-C 1, Naval Education and Training Professional Development and Technology Center, Pensacola, FL, 1979.
INDEX-1
INDEX-2
INDEX-3
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
ASSIGNMENT 1 Textbook assignment: Chapter 1, “Radar Fundamentals,” pages 1-1 through 1-45.
1-1. Radar uses what form of energy to detect ships, planes, and land masses?
1. Sound waves 2. Visible light 3. Infrared radiation 4. Electromagnetic energy
1-2. What radar measurement of an object is referenced to true north?
1. Height 2. Surface angle 3. Vertical angle 4. One-way distance
1-3. The elevation angle to the target is the angle between which of the following references?
1. Ship's heading and line of sight 2. Vertical plane and line of sight 3. Horizontal plane and line of sight 4. Vertical plane and horizontal plane
1-4. Electromagnetic energy travels through air at approximately what speed?
1. 984 feet per microsecond 2. 186,000 statute miles per second 3. 162,000 nautical miles per second 4. Each of the above is correct
1-5. For an object that is detected 15 miles from a radar set, what is the approximate time required for the rf energy to travel to and return from the object?
1. 7 microseconds 2. 185 microseconds 3. 271 microseconds 4. 927 microseconds
1-6. The minimum range of a radar depends on the length of time of the transmitter pulse (pulse width) and recovery time. During this period, the radar can NOT receive energy. A radar set with a pulse width of 5 microseconds and a recovery time of 0. 2 microseconds has a minimum range of approximately
1. 614 yards 2. 787 yards 3. 852 yards 4. 4,100 yards
1-7. Of the following radar characteristics, which has NO effect on maximum range capability?
1. Recovery time 2. Carrier frequency 3. Receiver sensitivity 4. Pulse-repetition frequency
1-8. Which of the following characteristics of a radar system determines the degree to which the radiated energy is affected by atmospheric conditions?
1. Pulse peak power 2. Carrier frequency 3. Receiver sensitivity 4. Pulse-repetition frequency
1-9. Pulse-repetition time is described as the
1. reciprocal of pulse width 2. period of time from the beginning to
the end of a transmitter pulse 3. period of time required for the pulse
to travel to the target and return 4. period of time from the beginning of
2
1-10. Which of the following terms describes radar returns that exceed the prt of the radar?
1. Clutter 2. Ambiguous 3. Reciprocal 4. Acquisition
1-11. What type of transmitter power is measured over a period of time?
1. Peak 2. Return 3. Average 4. Reciprocal
1-12. Which of the following formulas can be used to compute the duty cycle of a radar set?
1.
2.
3.
4.
IN ANSWERING QUESTIONS 1-13 AND 1-14, ASSUME THAT A RADAR SET HAS THE FOLLOWING CHARACTERISTICS: AVERAGE POWER = 700 WATTS PULSE WIDTH = 3. 5 MICROSECONDS PRF = 400 HERTZ
1-13. What is the peak power (in kilowatts) for this radar set?
1. 500 2. 1,500 3. 2,000 4. 2,500
1-14. What is the pulse-repetition time (in microseconds) for this radar set?
1. 1,500 2. 2,000 3. 2,500 4. 4,000
1-15. For a radar set with a pulse width of 25 microseconds and a prf of 600 pulses per second, what is the duty cycle?
1. 0.015 2. 0.024 3. 0.15 4. 0.24
1-16. What is the maximum radar horizon distance for a radar set with an antenna 100 feet above the surface of the earth?
1. 8 miles 2. 12.5 miles 3. 80 miles 4. 125 miles
1-17. A radar set with a prf of 1,000 pps and an antenna rotation rate of 15 rpm produces what maximum number of pulses per degree?
1. 2.7 2. 11.1 3. 14.4 4. 36
1-18. The relative bearing of a radar echo is measured with respect to which of the following reference points?
1. True north 2. Magnetic north 3. Centerline of your own ship 4. The position of the antenna
3
1-19. Altitude- or height-finding radar systems require a beam with which of the following characteristics?
1. Narrow in the vertical plane 2. Narrow in the horizontal plane 3. Broad in the horizontal plane 4. Broad in the vertical plane
1-20. Target resolution is the ability of a radar to distinguish between targets that are at nearly the same range and/or bearing. Range resolution is dependent on which of the following factors?
1. Peak power and beam width 2. Pulse width and beam width 3. Pulse width and target size 4. Peak power and target size
1-21. What is the approximate range resolution (in yards) of a radar set with a pulse width of 15 microseconds and a peak power of 2 kilowatts?
1. 10 2. 24 3. 1,093 4. 2,460
1-22. The width of a radar beam and range to a detected object are the determining factors in which of the following radar system characteristics?
1. Range resolution 2. Bearing resolution 3. Beam half-power points 4. Altitude detection accuracy
1-23. Which of the following factors has/have the greatest effect on the accuracy of a pulse radar?
1. Resolution 2. Average power 3. Atmospheric conditions 4. Each of the above
1-24. To detect nearby objects, the output pulse of a radar transmitter should possess which of the following characteristic shapes?
1. Narrow and square 2. Narrow with a sloping trailing edge 3. Wide and trapezoidal 4. Wide and square
1-25. Refractions and speed changes are known to occur in electromagnetic wavefronts. These phenomena are caused by which of the following conditions?
1. Temperature 2. Vapor content 3. Atmospheric pressure 4. All of the above
1-26. Temperature inversions and/or moisture lapses in the atmosphere may extend or reduce the range of a radar by creating
1. ducts 2. ionic layers 3. surface waves 4. reflective layers
1-27. In a pulse radar system, which of the following components should you expect to find?
1. Synchronizer and transmitter 2. Duplexer and antenna system 3. Receiver and indicator 4. All of the above
1-28. In a pulse radar system, what component controls timing throughout the system?
1. Power supply 2. Synchronizer 3. Indicator 4. Receiver
4
1-29. What component of the transmitter supplies the trigger pulse, which acts as a switch to turn the klystron on and off?
1. Magnetron 2. Modulator 3. Indicator 4. Power supply
1-30. Which of the following radar components allows the use of one antenna for both transmitting and receiving radar energy?
1. Synchronizer 2. Modulator 3. Duplexer 4. Mixer
1-31. To make amplification of received rf energy easier, the returning rf signal is converted to a lower, intermediate frequency. What component of the radar system performs this function?
1. A duo-diode duplexer 2. A three-stage synchronizer 3. A cross-field amplifier 4. A superheterodyne receiver
1-32. The sweep frequency of a radar indicator is determined by what parameter of the radar system?
1. Duty cycle 2. Pulse width 3. Carrier frequency 4. Pulse-repetition frequency
1-33. The type and method of scanning used by a radar system depend upon which of the following radar system design considerations?
1. Antenna size 2. Type of radar 3. Purpose of the radar 4. All of the above
1-34. In a single stationary-lobe scanning system, complete azimuth coverage is achieved by which of the following methods?
1. Multiple overlapping beams 2. An omnidirectional antenna 3. A continuously rotating antenna 4. Very wide, flat beams
1-35. Which of the following methods can be used to achieve radar-beam scanning?
1. Mechanical 2. Electronic 3. Combined mechanical and electronic 4. Each of the above
1-36. In a conical-scan antenna, nutation of the radar beam is usually accomplished by which of the following methods?
1. By moving the reflector 2. By moving the feed point 3. By varying the signal phase at the
feed point 4. By moving both the feed point and
1-37. At any given distance from the antenna, the radar beam axis of a conical-scan antenna follows what pattern?
1. A circle around the scan axis 2. An ellipse in the vertical plane 3. An ellipse in the horizontal plane 4. Two circles covering the scan axis in
1-38. In a monopulse scanning radar, the relative position of a target with respect to the radar-beam axis is determined by comparing which of the following signal components?
1. The phases of the radiated rf energy 2. The phases of the returning rf energy 3. The amplitudes of the returning rf
energy in each horn 4. The amplitudes of the returning rf
5
1-39. In a monopulse scanning system, which of the following feedhorn signal combinations makes up the bearing signal?
1. (A + D) - (A + C) 2. (A + B) - (C + D) 3. (A + C) - (B + D) 4. A + B + C + D
1-40. In a monopulse scanning system, which of the following combinations make up the range signal?
1. (A + D) - (A + C) 2. (A + B) - (C + D) 3. (A + C) - (B + D) 4. A + B + C + D
1-41. Monopulse receivers use what signal as a phase reference?
1. Range 2. Traverse 3. Elevation 4. Angle-tracking
1-42. In the cw radar transmission method, the Doppler effect provides which of the following target information?
1. Speed of the target 2. Presence of the target 3. Both 1 and 2 above 4. Relative bearing of the target
1-43. The frequency of the returned signal increases when a target is approaching and decreases when a target is moving away in which of the following types of radar systems?
1. Search 2. Doppler 3. Pulse-modulation 4. Frequency-modulation
1-44. Continuous-wave radar that uses the Doppler effect is best used in detecting which of the following types of targets?
1. Stationary 2. Past-moving 3. Targets with a high degree of range
resolution 4. Targets with a high degree of bearing
1-45. Range information can be obtained in a Doppler radar by which of the following methods?
1. Sweeping the transmitter frequency 2. Using two separate transmitters 3. Both 1 and 2 above 4. Using two separate antennas
1-46. Frequency-modulated radars transmit a wave that continuously changes in frequency about a center frequency. Using frequency modulation, the range to a target is determined by using which of the following methods?
1. By comparing the frequency of the transmitted signal with the returned frequency from the target
2. By comparing the magnitude of transmitted pulses with the magnitude of returned pulses
3. By comparing the velocity of the received energy with the velocity of the transmitted energy
4. By measuring the Doppler shift that occurs in the returning signal
6
1-47. Which of the following statements describes the advantage of using pulse modulation (pm) rather than continuous- wave (cw) in a radar system?
1. Pm may be used to detect moving targets; cw is effective only against stationary targets
2. Pm may be used to determine relative velocity much more accurately than cw
3. Pm does not require frequency stabilization of the carrier wave; cw does
4. Pm does not depend on target motion; cw does
1-48. In Doppler radar, some definite relationship must exist between the transmitted frequency and the reference frequency. For what purpose is this relationship used?
1. To detect the heterodyning signal 2. To detect the continuous-wave signal 3. To detect the Doppler shift of the
received signal 4. To detect the frequency shift of the
1-49. Which of the following JETDS classifications identifies a shipboard fire control radar set?
1. AN/SPS-39 2. AN/SPG-55 3. AN/APG-12 4. AN/MRC-20
1-50. For most military applications, which of the following radar systems is/are used?
1. Track radar only 2. Search radar only 3. Both track and search radars are used 4. Moving-target indicators
1-51. Detection of surface and low-altitude air targets is the primary purpose of which of the following types of radar?
1. Surface search 2. Height finding 3. Fire control 4. Air search
1-52. Which of the following are typical characteristics of surface-search radars?
1. High pulse-repetition rates 2. Narrow pulse widths 3. High frequencies 4. All of the above
1-53. Long-range aircraft detection is provided by which of the following types of radar?
1. Track 2. Air search 3. Fire control 4. Surface search
1-54. Which of the following are characteristics of a typical air-search radar?
1. Low frequency 2. Narrow pulse width 3. High pulse-repetition rate 4. All of the above
1-55. Which of the following types of radar provides accurate range, bearing, and altitude of aircraft?
1. Air search 2. Guidance 3. Height-finding 4. Surface search
1-56. Which of the following radars would most likely be used to direct CAP aircraft during an intercept?
1. Track radar 2. Fire-control radar 3. Surface-search radar 4. Three-coordinate radar
7
1-57. The range capability of a 3D radar is limited by which of the following characteristics?
1. Low prf 2. Long prt 3. Low output power 4. High operating frequency
1-58. Fire control radars must be directed to the general location of a desired target. This is because of which of the following characteristics?
1. Low output power level 2. Low degree of accuracy 3. Narrow beam pattern 4. Poor resolution
1-59. When a fire-control radar antenna approaches the general direction of a target, the radar enters which of the following modes of operation?
1. Acquisition 2. Designation 3. Lock-on 4. Track
1-60. Which of the following characteristics is/are typical of a fire-control radar?
1. Very high prf 2. Very narrow pw 3. Very narrow beam 4. All of the above
1-61. Complete control of a beam-rider missile requires what minimum number of radar beams?
1. 1 2. 2 3. 3 4. 4
8
Textbook assignment: Chapter 2, “Radar Subsystems,” pages 2-1 through 2-51. ___________________________________________________________________________________
2-1. Which of the following units of a radar system determines timing for all units of the radar?
1. Automatic tracker 2. Synchronizer 3. Transmitter 4. Receiver
2-2. Which of the following classifications describes a radar system that uses a master oscillator to produce timing pulses?
1. Externally synchronized 2. Self-synchronized 3. Unsynchronized 4. Free-running
2-3. Which of the following oscillators may be used as the master oscillator in a radar system?
1. A stable multivibrator 2. Sine-wave oscillator 3. Blocking oscillator 4. Each of the above
2-4. Which of the following oscillators, used in a synchronizer to provide timing trigger pulses, does NOT require a pulse- shaping circuit in its output?
1. Phase-shift oscillator 2. Square-wave oscillator 3. Sine-wave oscillator 4. Blocking oscillator
2-5. A radar system in which timing triggers are determined by the pulse-repetition rate of the modulator uses what type of synchronization?
1. Self 2. External 3. Free-running 4. Stable blocked
2-6. Which of the following radar indicator functions is/are controlled by gate pulses from the synchronizer?
1. Sweep duration 2. Sweep initiation 3. Range-mark generator gating 4. All of the above
2-7. Indicator sweep voltage in a radar is normally initiated at which of the following times?
1. At the same time as the transmitter trigger
2. Before the transmitter trigger 3. After the transmitter trigger 4. Each of the above
2-8. The flyback retrace of a radar system indicator is prevented from appearing on the cathode-ray tube by removing the
1. negative-intensity gate pulse applied to the control grid
2. positive-intensity gate pulse applied to the control grid
3. negative-intensity gate pulse applied to the cathode
4. positive-intensity gate pulse applied to the cathode
9
2-9. Which of the following characteristics is NOT a requirement of a basic radar system timing circuit?
1. It must be free-funning 2. Frequency must be variable 3. It must develop random frequencies 4. It should provide a stable frequency
2-10. Which of the following circuits converts square waves to positive and negative triggers?
1. A negative limiter 2. A positive limiter 3. A long-time-constant RC
differentiator 4. A short-time-constant RC
2-11. Which of the following circuits is used to remove either the negative or positive triggers from the output of a sine-wave oscillator?
1. A clipper 2. A limiter 3. An LC network 4. A differentiator
2-12. When the master oscillator in a multivibrator timer is asymmetrical, the output of the master oscillator is in the form of
1. rectangular waves 2. negative pulses 3. square waves 4. sine waves
2-13. The positive and negative output pulses of the astable multivibrator are sent to the indicator for which of the following purposes?
1. To intensify the crt beam 2. To gate the range-marker generator 3. Both 1 and 2 above 4. To gate the transmitter output
2-14. Which of the following oscillators generates sharp trigger pulses without additional circuitry?
1. Sine-wave oscillator 2. Wien-bridge oscillator 3. One-shot multivibrator 4. Single-swing blocking oscillator
2-15. A radar transmitter is triggered directly by high voltage pulses from what unit?
1. The timer 2. The antenna 3. The indicator 4. The modulator
2-16. The peak power of a transmitted rf pulse depends on which of the following factors?
1. Width of the modulator pulse 2. Amplitude of the modulator pulse 3. Prf of trigger pulses from the timer 4. Delay time between trigger and
2-17. The transmitter range timing circuit must be triggered at the instant the transmitted pulse leaves the transmitter. For which of the following reasons is this timing so important?
1. To ensure accurate range 2. The ensure long range targets are
detected 3. To ensure that the target is "painted"
on the crt by each transmitted pulse 4. To keep the magnetron oscillating at
2-18. For proper operation of the magnetron, the modulator pulse must have which of the following characteristics?
1. A flat top 2. A steep leading edge 3. A steep trailing edge 4. All of the above
10
2-19. In order that nearby targets may be detected, which of the following characteristics must the transmitted pulse have?
1. A steep leading edge 2. A steep trailing edge 3. A sloping leading edge 4. A sloping trailing edge
2-20. Compared to the hard-tube modulator, the line-pulsing modulator has which of the following advantages?
1. It is more complex 2. It is more efficient 3. It is more sensitive to voltage
changes 4. It requires a higher power-supply
2-21. The modulator of a radar basically consists of a power supply, a switch, a storage element, and a/an
1. IF strip 2. oscillator 3. transmitter 4. charging impedance
2-22. Which of the following devices can be used as the storage element in a radar modulator?
1. A capacitor 2. A pulse-forming network 3. An artificial transmission line 4. Each of the above
2-23. A signal introduced at the input end of an artificial transmission line moves through the circuit to the output end and is reflected back to the input. The output end of an artificial transmission line appears to the input signal as what type of circuit?
1. Open 2. Short 3. Inductive reactance 4. Capacitive reactance
2-24. The discharge pulse from the artificial transmission line causes a voltage of what magnitude to appear across the primary of the pulse transformer?
1. Twice the original charge voltage 2. One-half the original charge voltage 3. The same as the original charge
voltage 4. One-fourth the original charge
2-25. What parameter, if any, of the output pulse from an artificial transmission line is affected by the inductance and capacitance of each section of the line?
1. Width 2. Amplitude 3. Frequency 4. None of the above
2-26. A pulse-forming network exhibits electrical behavior similar to which of the following devices?
1. A resistance-capacitance network 2. An artificial transmission line 3. A capacitor 4. An inductor
2-27. The requirements of a modulator switch are to (1) reach full conduction quickly, (2) consume low power, (3) start and stop conduction suddenly, and (4) conduct high currents and handle high voltages. Which of the following tubes meets these requirements?
1. A tetrode 2. A thyratron 3. A magnetron 4. A beam-powered amplifier
11
2-28. What modulator circuit characteristic determines the charging rate of the storage element?
1. Resistance 2. Capacitance 3. Charging impedance 4. Pulse-repetition frequency
2-29. Which of the following types of instability are common to magnetron oscillators?
1. Mode skipping 2. Mode shifting 3. Both 1 and 2 above 4. Magnetic fluctuation
2-30. Which of the following magnetron characteristics can be caused by low magnetic field strength?
1. Low power output 2. Excessive plate current 3. Incorrect operating frequency 4. All of the above
2-31. Which of the following maximum tuning ranges is typical for a tunable magnetron?
1. – 10 percent around the center frequency
2. – 5 percent around the center frequency
3. 1 to 5 percent above the center frequency
4. 1 to 10 percent below the center frequency
2-32. Compared to the keyed-oscillator transmitter, power-amplifier transmitters are used more often with mti radar systems because power-amplifier transmitters provide
1. better stability 2. lower output power 3. higher output power 4. greater frequency range
2-33. Which of the following tubes should be used as the power amplifier in a radar transmitter?
1. The magnetron 2. The thyratron 3. The reflex klystron 4. The multicavity klystron
2-34. Which of the following components determines the pulse width of a power- amplifier transmitter?
1. The modulator 2. The mixer-amplifier 3. The local oscillator 4. The power-amplifier tube
2-35. The intermediate stages of a power- amplifier transmitter have operating power only during which of the following times?
1. When the coherent rf pulse is applied 2. When the local oscillator signal is
applied 3. During the time the modulator pulse
is applied 4. Immediately after the coherent rf
2-36. Using a frequency synthesizer instead of a heterodyning mixer as the frequency generating source for a power-amplifier transmitter is an advantage because the frequency synthesizer
1. is more stable 2. is simpler to construct 3. produces a single frequency 4. produces discrete frequencies over a
12
2-37. Unwanted oscillations in an rf amplifier transmitter are prevented because of which of the following pulse relationships?
1. The rf pulse is wider than the modulator pulse
2. The rf pulse is narrower than the modulator pulse
3. The rf pulse frequency is equal to the local oscillator frequency
4. The rf pulse frequency is less than the local oscillator frequency
2-38. A power-amplifier transmitter that transmits a broad band of frequencies typically uses which of the following tubes as the final stage?
1. A crossed-field amplifier 2. A multicavity klystron 3. A magnetron 4. A twt
2-39. What is the primary function of the radar duplexing system?
1. To prevent the formation of standing waves in the waveguide system
2. To permit the use of one antenna for transmission and reception
3. To increase the effective range of the radar
4. To increase antenna directivity
2-40. A defective duplexer in a radar will most likely cause damage to which of the following components?
1. The receiver 2. The waveguide 3. The magnetron 4. The local oscillator
2-41. Why is it desirable that the duplexer quickly connect the receiver to the antenna after the transmitted pulse?
1. So that line-match will remain balanced
2. So that the transmitter power dissipated will be minimum
3. So that echoes from nearby targets will be received
4. So that echoes from nearby targets will not prolong ionization
2-42. The action of tr-atr circuits depends upon the impedance characteristics of which of the following lengths of transmission line segments?
1. 1 wave length 2. 1/2 wave length 3. 1/4 wave length 4. 1/8 wave length
2-43. Which of the following requirements is/are essential for proper tr spark gap operation?
1. High impedance during arc time 2. Low impedance during arc time 3. High impedance prior to arc time 4. Both 2 and 3 above
2-44. What is the purpose of introducing water vapor into a tr tube?
1. It increases recovery time 2. It prevents early ionization 3. It decreases deionization time 4. It increases the gap breakdown
13
2-45. Keep-alive voltage is applied to the tr tube for which of the following reasons?
1. To maintain ionization within the tube after the breakdown voltage is removed
2. To ensure that the tube will rapidly return to the deionized state
3. To maintain a glow discharge within the tube so that firing will occur rapidly
4. To prevent breakdown within the tube prior to pulse transmission so that firing will not be premature
2-46. Atr tubes generally have a longer duty life than tr tubes because atr tubes do NOT use
1. radioactive materials and chemically active gas
2. chemically active gas and keep-alive voltages
3. keep-alive voltages and radioactive materials
4. keep-alive voltages and pure inert gas
2-47. In a series-connected duplexer, what spark gap, if any, fires during reception?
1. The tr only 2. The atr only 3. Both the tr and atr 4. None of the above
2-48. Indirectly coupled waveguide duplexers are normally connected to the main waveguide by which of the following devices?
1. A two-wire line 2. A coaxial cable 3. A short quarter-wave stub 4. A short section of waveguide
2-49. The direct-coupled waveguide duplexer is connected to the waveguide at the location of
1. minimum current flow 2. minimum magnetic field intensity 3. maximum magnetic field intensity 4. maximum electric field intensity
2-50. In a hybrid-ring duplexer, the fields at the entrance of an arm must have what phase relationship to propagate energy down the arm?
1. 0 degrees 2. 90 degrees 3. 180 degrees 4. 270 degrees
2-51. Which of the following are requirements of a microwave receiver?
1. Amplify extremely high-frequency pulses
2. Detect and amplify pulses in the microvolt range
3. Detect pulses with a duration of a few microseconds
4. All of the above
2-52. The maximum range at which a radar receiver can detect an object is limited by which of the following factors?
1. Noise 2. Signal distortion 3. Receiver bandwidth 4. Transmitter frequency
2-53. An effective radar receiver should have a gain factor that is in which of the following ranges?
1. 101 to 102
2. 103 to 104 3. 106 to 108 4. 109 to 1010
14
2-54. An overdriven amplifier stage in a receiver may cause which of the following conditions?
1. Blocking 2. Inaccurate ranges 3. Increased sensitivity 4. Large signal distortion
2-55. The intermediate frequency is produced in what stage of a microwave receiver?
1. The mixer 2. The IF amplifier 3. The second detector 4. The local oscillator
2-56. What section of a radar receiver usually determines the overall bandwidth?
1. The mixer 2. The IF amplifier 3. The video amplifier 4. The local oscillator
2-57. What component in a receiver afc circuit produces an output voltage proportional in amplitude and polarity to any change in the intermediate frequency?
1. The mixer 2. The IF amplifier 3. The discriminator 4. The local oscillator
2-58. An efficient local oscillator must have which of the following characteristics?
1. Tunable frequency 2. Stable output frequency 3. Operation in the 4,000 megahertz
range 4. All of the above
2-59. Which of the following devices would be used as a local oscillator in a radar receiver?
1. A magnetron 2. A crystal diode 3. A reflex klystron 4. A parametric amplifier
2-60. Which of the following advantages is gained by using a crystal mixer in a microwave receiver?
1. Less noise 2. Reduced saturation 3. Increased overall gain 4. Improved oscillator stability
2-61. The resonant circuit at the output of an unbalanced crystal mixer serves which of the following purposes?
1. It amplifies the IF signal 2. It produces the IF signal 3. It eliminates unwanted signals 4. It amplifies the local oscillator signal
2-62. The balanced transformer connected to the crystals of a balanced mixer has a secondary that is tuned to what frequency?
1. The desired IF 2. The local oscillator frequency 3. The afc discriminator frequency 4. The transmitter carrier frequency
2-63. The IF amplifier stage of a radar receiver determines which of the following receiver characteristics?
1. The gain 2. The effective bandwidth 3. The signal-to-noise ratio 4. All of the above
15
2-64. The detector in a radar receiver converts the IF pulses into what form?
1. Video pulses 2. Square waves 3. Dc voltage levels 4. Continuous-wave signals
2-65. Agc automatically adjusts the gain of the receiver by controlling which of the following quantities?
1. Detector bias 2. IF amplifier bias 3. Mixer output signal level 4. Video amplifier output signal level
2-66. A radar receiver uses iagc for which of the following purposes?
1. To reduce the amplitude of echoes from distant targets
2. To prevent full amplification of strong signals
3. To permit full amplification of weak signals
4. Both 2 and 3 above
2-67. In a radar receiver, which of the following purposes is served by using stc?
1. Prevents full amplification of echoes from nearby targets
2. Permits full amplification of echoes from distant targets
3. Both 1 and 2 above 4. Prevents target echoes within a
2-68. In the input of the first video amplifier of a radar receiver, the differentiator circuit performs which of the following functions?
1. Ftc 2. Gagc 3. Afc 4. Iagc
2-69. The primary function of the mti system is to display which of the following types of targets?
1. Moving targets only 2. Motionless targets only 3. Moving and motionless targets
during each sweep 4. Moving and motionless targets
2-70. Delaying the received signals in the mti system permits them to be combined with the next set of received signals so that only desired signals are displayed. The signals displayed are formed by which of the following methods?
1. Division 2. Addition 3. Subtraction 4. Multiplication
2-71. In the mti system, what is the purpose of the coho lock pulse?
1. To synchronize the coho and transmitted frequency phase relationship
2. To control the transmitter pulse- repetition frequency
3. To synchronize the phase of the timing circuits with the phase detector
4. To control the polarity of the coherent video
2-72. The amplitude of coherent video is determined by the phase difference between which of the following signals?
1. Coho reference and transmitted pulse 2. Coho reference and coho lock pulse 3. Coho reference and IF echo 4. IF echo and received echo
16
2-73. The purpose of the mti system timing circuits is to
1. synchronize the coho and transmitted frequency phase relationship
2. control the transmitter pulse- repetition frequency
3. synchronize the phase of the video balancer with the phase detector
4. select the polarity of the coherent video
2-74. The lin-log amplifier provides (a) a linear output voltage for what amplitude of input signal and (b) a logarithmic output voltage for what amplitude of input signal?
1. (a) Low (b) low 2. (a) Low (b) high 3. (a) High (b) high 4. (a) High (b) low
2-75. What channel in a monopulse receiver is used as the reference channel?
1. IF 2. Range 3. Bearing 4. Elevation
17
ASSIGNMENT 3 Textbook assignment: Chapter 3, “Radar Indicators and Antennas,” pages 3-1 through 3-22. Chapter 4,
“Radar Maintenance,” pages 4-1 through 4-23. ___________________________________________________________________________________
3-1. Which of the following geometrical quantities is/are used as coordinates for radar displays?
1. Range 2. Bearing 3. Elevation 4. All of the above
3-2. Of the following target parameters, which would most likely be displayed on all radar sets?
1. Altitude 2. Slant range 3. Ground range 4. All of the above
3-3. Which of the following quantities determines total distance represented on a crt display.
1. Crt size 2. Sweep speed 3. Sweep length 4. Echo spacing
3-4. To correctly represent the location of a target, a radar repeater must receive which of the following quantities?
1. Video 2. Timing pulses 3. Antenna information 4. All of the above
3-5. The A-scope crt normally uses what type of sweep deflection?
1. Mechanical 2. Electrostatic 3. Electromagnetic 4. Electromechanical
3-6. The rhi scope provides the operator with information concerning the target's
1. range only 2. altitude only 3. range and altitude 4. range and bearing
3-7. Own ship position is at the center of the scope in which of the following radar displays?
1. A-scope 2. B-scope 3. Rhi scope 4. Ppi scope
3-8. Synchronization of events in ppi circuitry is of special importance for which of the following reasons?
1. To ensure that bearing readings are accurate
2. To ensure that range readings are accurate
3. To ensure the deflection coils do not overheat
4. To ensure the power supply is activated at the instant the transmitter fires
3-9. Pulses used to synchronize the ppi with the transmitter are developed in which of the following circuits?
1. Gate 2. Sweep control 3. Sweep generator 4. Intensity gate generator
18
3-10. Which of the following circuits produces currents that deflect the electron beam across the crt?
1. Gate 2. Sweep control 3. Sweep generator 4. Intensity gate generator
3-11. Electromagnetic deflection is preferred over electrostatic deflection in ppi scopes because it provides which of the following advantages?
1. Better control of the beam 2. Better beam position accuracy 3. Better deflection sensitivity 4. All of the above
3-12. Focusing is accomplished in an electromagnetic crt by varying the
1. potential on the deflection plates 2. potential between the first anode and
the cathode 3. current through the coil around the
neck of the tube 4. do bias current in the deflection coils
3-13. Because the electromagnetic crt uses magnetic deflection, the sweep circuits must provide the deflection coils with which of the following signals?
1. Linear trace current 2. Trapezoidal voltage 3. Sinusoidal voltage 4. Direct current
3-14. In a ppi scope that uses electromagnetic deflection, the amplitudes and polarities of the sawtooth currents are determined by which of the following inputs?
1. Target position and speed 2. Antenna rotation speed 3. Antenna position 4. Both 2 and 3 above
3-15. On the screen of a ppi scope, range markers appear as
1. vertical pulses 2. radial grid lines 3. concentric circles 4. horizontal grid lines
3-16. The range sweep in a range-gate generator is started at the same time the transmitter fires. A pulse from which of the following circuits causes this timing?
1. Receiver 2. Indicator 3. Transmitter 4. Synchronizer
3-17. When used with a ppi presentation, a range gate must have which of the following characteristics?
1. Movable in range 2. Movable in bearing 3. Both 1 and 2 above 4. Fixed in range and bearing
3-18. Range-markers are produced on the basis of which of the following timing constants?
1. Radar mile 2. Transmitter prf 3. Receiver bandwidth 4. Transmitter pulse width
3-19. To read range directly, the range step is placed in what position relative to an echo pulse?
1. The range step is centered on the echo pulse
2. The range step coincides with the leading edge of the echo pulse
3. The range step coincides with the trailing edge of the echo pulse
4. The range step covers the entire echo pulse
19
3-20. Compared to omnidirectional antennas, directional antennas provide which of the following advantages?
1. Power gain and selectivity 2. Power gain and directivity 3. Sensitivity and selectivity 4. Sensitivity and directivity
3-21. If the vertical beam width of a radar antenna is decreased, what will be the effect on (a) power gain and (b) vertical directivity?
1. (a) Decrease (b) decrease 2. (a) Decrease (b) increase 3. (a) Increase (b) increase 4. (a) Increase (b) decrease
3-22. An array of twelve dipoles are set in the same position as a reference dipole and are fed with the same line. The power gain will be
1. less than unity 2. one-twelfth the reference 3. twelve times the reference 4. dependent on the directivity of the
3-23. If the slant range and altitude of a target are known, which of the following coordinates can be computed using trigonometric functions?
1. Elevation angle 2. True-bearing angle 3. Relative-bearing angle 4. All of the above
3-24. To convert diverging waves into parallel waves, where must the radiating element be placed in relation to a parabolic reflector?
1. At the focal point of the reflector 2. 1/4 wavelength from the reflector 3. 1/2 wavelength from the reflector 4. At the focal point of the
3-25. What is the function of the hemispherical shield of the parabolic reflector?
1. To polarize all reflected waves in the vertical plane
2. To polarize all reflected waves in the horizontal plane
3. To convert the spherical waves radiated by the dipole into vertical lines of rf energy
4. To reflect rf energy radiated forward of the dipole back to the parabolic reflector
3-26. Which of the following types of parabolic reflectors has a focal line rather than a single focal point?
1. Truncated 2. Rotational 3. Orange-peel 4. Cylindrical
3-27. A broadside array causes maximum energy to be radiated perpendicular to the plane of the dipole for which of the following reasons?
1. Because dipoles are excited in phase with each other
2. Because dipoles are parallel to each other
3. Because dipoles are 1/2 wavelength apart
4. Because dipoles are 1/8 wavelength away from the reflector
3-28. The directivity of a horn radiator is dependent on which of the following physical dimensions of the horn?
1. The shape 2. The length 3. The mouth size 4. All of the above
20
3-29. Feedhorn shadows can be eliminated by taking which of the following actions?
1. By making the horn smaller 2. By making the reflector smaller 3. By offsetting the horn from the
center of the reflector 4. By putting the horn behind the
3-30. Airborne radars have unique physical design requirements. Which of the following functions is performed by the radome?
1. It serves as the antenna 2. It provides aerodynamic shape 3. It protects the antenna from low air
pressure 4. All of the above
3-31. If a fixed-frequency radar transmitter is found to be off its normal operating band, which of the following corrective actions should be taken?
1. Retune the transmitter 2. Change the assigned frequency 3. Replace the defective part causing
the error 4. Check the frequency again, an error
3-32. If a transmitter carrier wave is modulated by a square wave, what maximum number of different frequencies will be produced?
1. An infinite number 2. 2 3. 3 4. 4
3-33. Which of the following statements describes a radar transmitter frequency spectrum?
1. The distribution of energy over a band of frequencies
2. The distribution of energy over time 3. The prf multiplied by the duty cycle 4. The pulse width versus peak power
3-34. What total number of modulating components are present in the output spectrum of a pulse radar transmitter?
1. 1 2. 2 3. 3 4. 4
3-35. An ideal radar frequency spectrum would be best described in which of the following ways?
1. It is symmetrical 2. It has a wide lobe 3. It has narrow side lobes 4. It has no minimum points
3-36. In a good spectrum curve the distance between the two minima is proportional to which of the following transmitter parameters?
1. Prt 2. Prf 3. Peak power 4. Pulse width
3-37. The echo box is a good instrument for measuring overall radar system performance because it indicates the combined effectiveness of which of the following components?
1. Antenna and duplexer 2. Transmitter and antenna 3. Transmitter and receiver 4. Receiver and synchronizer
21
3-38. Oscillations in an echo box are known as ringing. Which of the following conditions cause this ringing?
1. A weak transmitter 2. A saturated receiver 3. A normally operating receiver 4. A normally operating transmitter
3-39. What constitutes the single most useful measurement you can make with the echo box?
1. Ring time 2. Duty cycle 3. Power distribution 4. Frequency distribution
3-40. Desirable transmitter output power characteristics include what relative levels of (a) peak power and (b) average power?
1. (a) Low (b) low 2. (a) Low (b) high 3. (a) High (b) high 4. (a) High (b) low
3-41. Most transmitter power readings are referenced to which of the following quantities?
1. 1 microwatt 2. 1 milliwatt 3. 1 watt 4. 1 kilowatt
3-42. Which of the following factors determines the overall performance of a radar receiver?
1. Bandwidth 2. Sensitivity 3. Recovery time of the tr 4. All of the above
3-43. Of the following receiver special circuits, which one is used during sensitivity tests?
1. Afc 2. Agc 3. Ftc 4. Iagc
3-44. The ability of a receiver to detect weak signals can be determined by which of the following measurements?
1. Noise figure 2. Minimum discernable signal 3. Both 1 and 2 above 4. Bandwidth
3-45. When several mds checks are to be taken over a period of time, the length of the test pulse used in the tests should
1. be the same on each check 2. be different on each check 3. vary with the transmitter pulse length
on each check 4. vary with the noise figure on each
3-46. When expressing the sensitivity of a radar receiver, which of the following quantities is used?
1. The signal generator reading 2. The combined attenuation value of
3. The sum of both 1 and 2 above 4. The attenuation value of the signal
3-47. Tr recovery time places limits on which of the following quantities?
1. Minimum range 2. Maximum range 3. Receiver bandwidth 4. Receiver sensitivity
22
3-48. Which of the following methods is/are used to determine the effectiveness of a tr tube?
1. Measure the keep-alive current 2. Measure the keep-alive voltage 3. Graph the correlation between
recovery time and leakage power 4. All of the above
3-49. The presence of standing waves on a transmission line indicates which of the following conditions?
1. Excessive output power 2. An impedance mismatch 3. Excessive pulse width 4. Excessive prf
3-50. Of the following conditions, which would be a likely indication of a high vswr?
1. Insufficient reflection 2. Cold spots in the transmission line 3. Arc-over at the maximum points 4. All of the above
3-51. Most primary shipboard ac distribution systems provide which of the following types of electrical power?
1. 60 Hz, 3 phase, ungrounded 2. 60 Hz, 1 phase, ungrounded 3. 400 Hz, 1 phase, ungrounded 4. 400 Hz, 3 phase, ungrounded
3-52. If your equipment is missing a certain voltage input, which of the following actions should you take first?
1. Call an electrician 2. Energize the emergency generator 3. Check the input to the switchboard 4. Check the power panel that feeds
3-53. What is the normal source of dry air for a shipboard radar system?
1. Compressed-air bottles 2. Central dry-air system 3. Dehumidifying ovens 4. Local dehydrators
3-54. The air control panel is designed to regulate
1. flow 2. purity 3. pressure 4. dew point
3-55. Which of the following units may be available as an emergency back-up to the central dry-air system?
1. Nitrogen tank 2. Local dehydrator 3. Local compressor-dehydrator 4. Each of the above
3-56. Which of the following methods is used to cool radar system components?
1. Air blowers 2. Liquid-cooling loops 3. Air-conditioning systems 4. Each of the above
3-57. A radar cooling system has a low-flow alarm in the sea-water loop. What is the primary purpose of this alarm?
1. It allows correction before damage occurs
2. It increases the flow in the distilled- water loop
3. It removes power from the system 4. It increases the sea-water pressure
23
3-58. Which of the following characteristics of cooling water for electronic equipment must be carefully controlled?
1. Purity 2. Pressure 3. Quantity 4. All of the above
3-59. For which of the following reasons do personnel sometimes develop a false sense of security concerning exposure to radiation?
1. Rf radiation does not always produce pain
2. Rf radiation is visible only at night 3. Only search radars are hazardous 4. Rf hazards occur only at night
3-60. Injury from X-rays would most likely result from which of the following actions?
1. Standing near unshielded high- voltage components
2. Working alone on low-voltage power supplies
3. Bypassing interlocks on shielded equipment
4. Working too close to a crt with a potential of 1,500 volts


Flowers not only have the power of cheering us up when we are feeling down, but they also have many other properties such as helping us get a proper night of sleep, boosting our creativity, increasing our productivity, making our tolerance to pain higher, boosting our health, and even improving our attention span. The researches demonstrate that workers’ idea generation, creative performance and problem-solving skills improve substantially in workplace environments that include flowers and plants. Classrooms with flowers and plants in it have a bigger attendance span, and students show more creativity, free-thinking skills, and overall satisfaction. Fill your home with blooms to keep your mind distracted from the day-to-day stress of life. Place them in your bedroom to wake up to a soothing and cheering view every morning, or to help you get a nice and relaxing night of sleep (choose flowers like Lavender, Jasmine or Gardenia. Flowers also help you create intimate connections and strengthen bonds with family and friends, which, ultimately, leads to a happier, more fulfilled life. COLOR-CHARACTERISTICS: In addition, color plays a big part in the emotion conveyed when sending flowers. According to Leatrice Eiseman, Executive Director of the Pantone Color Institute, “Our response to color is intensely emotional, and flowers can be a catalyst for feelings that stimulate more than just our senses of sight and smell.” Tradition dictates that certain flowers and colors are associated with specific occasions. However, in terms of emotional health, color choices take on different meanings. Red, traditionally associated with love and romance, has a positive effect on the immune system. Consider sending red flowers to someone who has recently had surgery, or experienced and illness. Red is also an energizing color for those who suffer from fatigue or exhaustion.


DynamoDBDocument client instance. Must be declared before configuring the model.
Regular expression to use when checking if the hash
key has the tenant
prefixed.
The name of the hash
key.
The type of the hash
key.
The name of the index to use when running an index
operation. By default
if will be called byGSIK
. If the index is not created before hand, and
the model is configured with a tenant
, then the method will fail.
The maximum GSIK values to use to index the models. This is necessary when
configuring a tenant
, since you can't configure an IAM policy to restrict
access to an item with a prefix on its hash ID. So, a GSIK will be
configured on every item by the library, using the tenant
value plus a
number between 0
and maxGSIK
. Then you can create an IAM policy that
restrict access on the index (called by defaylt byGSIK
) with access only
on the items with the appropiate GSIK value.
The name of the range
key.
The type of the range
key.
Struct instance created from the struct
data passed through the model
configuration.
The table name. If not provided it will try to use the table
name
globally configured.
The tenant
unique identifier.
Value used to track the dates where modifications were done to the item.
Generated using TypeDoc
Abstract class used to bootstrap a new Model.
Model
{IModel}


Redirecting to MTSvieweR (might take few seconds)
If it takes longer than 20 seconds, please contact with saeid.amiri@mcgill.ca


What’s that you’re drinking now?
Rate your drink and share with
the Glass society.
From your own list of booze,
tap, tap, tap to see which one you
love the most.
With world-best recommendation
algorithms (so far, at least!)
drinking will be even more fun.
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I enjoy Sculfin IPA from Ballast Point Brewery. What’s yours?
Top secret.
We are working and drinking very hard to release the official version. We expect to have it ready in 2015.
For iOS, you need at least iOS8, and for Android, you can check it now by visiting Google Play store.
Yes. They are undoubtedly accurate. We developed the most accurate recommendation engine in the world by using rating data and comparison data. This means that you can contribute to make it even better by being a member of the Glass society.
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I want to drink beer.
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My dream is to buy the Apple.
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...
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At least I draw 188 different views for this app.
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Recommendation is an art.
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RGB Color
Or pick a color:
Meals
Pizza
Lettuce (indoor): 3 seeds
Potatoo (outdoor): 4 seeds
Indoor Crops (hydroponics)
Lettuce
Harvest date:
2018-06-14
# Seeds:
Start
Outdoor Crops (farmbot)
Potatoo


---
layout: post
title: New Album Update
date: '2008-02-26T23:24:00.001-06:00'
author: Tom Ray
tags:
modified_time: '2008-02-26T23:24:58.863-06:00'
blogger_id: tag:blogger.com,1999:blog-11319466.post-6643823956147871372
blogger_orig_url: http://www.lorenzosmusic.com/2008/02/new-album-update.html
---
Well if you've been watching our netcasts you may have realized that we did not meet our Valentine's Day deadline for finishing the new album. Mark and I one night had a new song and decided we wanted to add it to the new album as well. It's been tracked and mixed and we're pretty happy with it. Although it did take a chunk of our time to do so. We are however done recording and mixing now, all that's left is mastering the tracks. So it's almost here.
In addition the artwork and design of the album and new website is underway too. We hope to be up and running very shortly. We will release the new songs on the website as soon as all this is finished and you will be able to purchase new CD's soon after that. We'll keep you posted.


Try to fetch this url as a bot (facebook, twitter, slack, etc) https://instafire-app.firebaseapp.com
https://instafire-app.firebaseapp.com


{% extends "git/base.html" %} {% load staticfiles %} {% block body %} {% regroup project.commit_set.all by commit_time|date as commit_list %}


What I've come to see as probably my greatest gift is the ability to take an extraordinarily complex, integrated, multidimensional problem and get arms around it conceptually in a way that helps, that informs and empowers practitioners to actually do things.
- Porter 2010
Porter's Five forces analysis is a framework that attempts to analyze the level of competition within an industry and business strategy development.


Abyssal Celebrant Undrias:
May the blessing of the abyss be with you!
The massive structure you see behind me is the Temple of Shilen where we serve Shilen, mother of the abyss. I am the Abyssal Celebrant Undrias who serves our goddess.
Ask about the Shilen Temple
Ask about the Dark Elf village
Quest


Commons Math Issue trackingCommons Math uses ASF JIRA for tracking issues. See the Commons Math JIRA project page. To use JIRA you may need to create an account (if you have previously created/updated Commons issues using Bugzilla an account will have been automatically created and you can use the Forgot Password page to get a new password). If you would like to report a bug, or raise an enhancement request with Commons Math please do the following:
Please also remember these points:
For more information on subversion and creating patches see the Apache Contributors Guide. You may also find these links useful: |


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