Module 18 - Radar Principles
Navy Electricity and Electronics Training Series (NEETS)
Chapter 4:  Pages 4-21 through 4-26

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.

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 loops?

Q21. What loop of a cooling system is often supplied by sea water?

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Safety

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.

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.

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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Figure 4-17. - Sample of one type of RADHAZ sign.

X-RAY EMIsSIONS

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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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.

Summary

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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