The term radome is a combination of the words radar and dome. Radomes are used to cover and protect radar antennas from environmental effects such as wind, rain, hail, snow, ice, sand, salt spray, lightening, heat, and erosion. The ideal radome is transparent to the RF radiation from the antenna and its return pulses and protects the antenna from the environment. A radome's design is based on the expected environmental factors and the mechanical and electronic requirements of the RF antenna.

Although, in theory, a radome may be invisible to RF energy, in real life the radome effects antenna's performance in four ways. These are; beam deflection, transmission loss, reflected power, and secondary effects. Beam deflection is the shift of the RF beam's axis. This is a major consideration with tracking (i.e. FC) radar. Transmission loss is the loss of energy associated with reflection and absorption within the radome. Reflected power can cause antenna mismatch in small radomes and sidelobes in large radomes. Depolarization and increased antenna noise are a result of secondary effects.

As an FC, you will be primarily responsible maintaining the radome associated with your equipment. This normally will include routine cleaning and inspection according to your prescribed preventive maintenance schedule. Some minor repairs may be authorized by your technical manuals, but most repairs will normally be done by an authorized factory representative. You may be required to repaint the radome because of normal environmental wear and tear. If so, be especially careful to use only paint(s) authorized by the manufacturer and to follow the authorized step-by-step procedures.

Figure 1-12 is an example of a radome in use in today's Navy. Other systems that use radomes include, the Combined Antenna System of the Mk 92 Fire Control System, the AN/SPQ-9 series antenna for the Mk 86 Gun Fire Control System, and the Mk 23 Target

Figure 1-12.-Example of a search and track radome.

Acquisitioning System for the SEASPARROW missile system.

Control Group

The Control Group provides computer control for an equipment group, processes target detections to develop and maintain a track file, and interfaces with the specific weapon system being used. The Control Group normally consists of the following equipment: a computer, data terminal set, magnetic tape unit, and test set.

Support Systems

The equipment we discussed above composes the core of the radar system. To operate properly and efficiently, it requires a certain amount of support equipment. Examples of such equipment include power supplies (some also have frequency converters), chilled water systems, and dry air systems. Although your radar system normally receives 440 VAC directly from the ship's primary power source, it has other voltage requirements that may be stepped up, stepped down, or converted in order to make the radar fully operational. High-voltage amplifiers and peripheral equipment associated with producing RF energy create tremendous amounts of heat. Chilled water systems remove excessive heat from such equipment. Cooling systems may be either liquid-to-liquid or liquid-to-air types that use either sea water, or chilled water provided by the ship itself. Another important support system is the dry air system. Dry air is used for keeping the internal part of the waveguide assembly moisture free and to aid in properly conducting the RF energy being transmitted. The dry air may be either air taken from ship spaces and circulated through various filters or dehydrated air provided by the ship. Some systems use a special gas for their waveguides. An example of this is the Mk 92 Fire Control System, which uses the gas SF6 for its Continuous Wave Illumination (CWI) mode.

These are very important support systems to your radar. As you know, any system is only as good as its weakest link. Therefore, you must be sure to maintain the support equipment as required by the equipment's technical manuals and maintenance instructions.

Stable Elements

Hitting a target on a regular basis requires that the gun or launcher be stable in relation to the target. Ideally, the platform on which the gun or launcher is mounted is stable throughout the target acquisition and destruction cycle. Unfortunately Navy ships, on which the guns and launchers are mounted, are seldom stable. In even the calmest sea, they pitch and roll to some extent. The solution lies in stabilizing the guns and launchers while the ship continues to pitch and roll. This is done with gyroscopes (gyros) installed in the fire control systems.

Gyros provide a stable platform, called the horizontal plane, as an unvarying reference from which the fire control problem is computed. The basic fundamentals and functions of gyros are covered in NEETS Module 15-Principles of Synchros, Servos, and Gyros.

In fire control, we call the stabilizing unit a stable element. As its name implies, the stable element uses a stabilizing gyro. The stabilizing gyro is also the primary reference for navigation of the ship. It gives the ship a true North reference for all navigational equipment. The WSN-2 or WSN-5 are examples of stabilizing gyros used in today's ships. The maintenance and operation of these gyros is the responsibility of the Interior Communications (IC) technicians. Figure 1-13 shows a phantom view of a gyro you might see on your ship.

The primary purpose of the stable element for fire control equipment is to measure accurately any deviation of the reference element (antenna, director, launcher, etc.) from the horizontal plane. Deviation measurements are sent to the fire control computer to create a stationary foundation from which to solve the fire control problem. They are also sent to the gun director, radar antenna, or optical equipment, depending upon the fire control system, to stabilize these units of the fire control system.

Q5. What is the switching time of a duplexer called?

Q6. What are the two types of lens antennas?

Q7. What determines the position of a phased array antenna beam?

Q8. What part of a radar system provides computer control for an equipment group?

Q9. What is the primary purpose of the stable element for fire control equipment?