Module 18—Radar Principles
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1-21 to 1-30
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1-41 to 1-45
, 2-1 to 2-10
2-11 to 2-20
, 2-21 to 2-30
2-31 to 2-40
, 2-41 to 2-51
3-1 to 3-10
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3-21 to 3-23
, 4-1 to 4-10
4-11 to 4-20
, 4-21 to 4-26
AI-1 to AI-11
, AII-1 to AII-2
Index-1 to 3
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.
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.
Figure 4-16.—Liquid cooling system block diagram.
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
Q21. What loop of a cooling system is often supplied by sea water?
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
RF RADIATION HAZARDS
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.
observe the following precautions to ensure that persons are not exposed to harmful RF radiation:
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
• 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.
loads should be employed where applicable in transmitting equipment during testing or checkout.
Figure 4-17.—Sample of one type of RADHAZ sign.
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.
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.
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.
Figure 4-18.—X-ray caution label.
• 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.
The SPECTRUM ANALYZER and the ECHO BOX are two instruments used to check
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.
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
You usually measure receiver sensitivity by measuring the MINIMUM DISCERNIBLE SIGNAL (MDS) using the pulse
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
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.
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
A4. Power and frequency.
A5. Average power, pulse width, and PRT.
A7. Transmitter power loss.
A8. Minimum discernible signal (MDS).
Attenuations of the directional coupler and the connecting cable.
A10. Half-power points.
A14. Manual bus transfer (MBT) unit.
backwards from the load to the source.
A16. Ship's central dry-air system.
A17. Degree of
A19. Air conditioning.
A20. Primary and secondary.
A21. The primary
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