Page:Electronics Technician - Volume 7 - Antennas and Wave Propagation - NAVEDTRA 14092.pdf/55

 platform 12 feet in diameter on the mast; the CV-3372/UPX position programmer is located above deck; and the C-10063/UPX antenna control is located below deck.

The array is vertically polarized and provides a minimum 13-decibel gain. The scan rate is 0-60 rpm with a maximum beam positioning time of 50 microseconds. The transmit frequency is 1,030 MHz and the receive frequency is 1,090 MHz.

The antenna has a total of 64 cavity-backed dipole radiators. It uses 16 radiators at a time to create the directional beam; by use of sequential grouping (1-16, 2-17, 3-18, etc), there are 64 groups possible. The groups are electronically coarse and fine steered by phase shifters. They can produce 1,024 equally spaced beam patterns with a horizontal width of 6.8 degrees and a vertical width of 42 degrees. Beam stabilization is 20 degrees maximum for roll and 12 degrees maximum for pitch. See figure 2-51.

RF SAFETY PRECAUTIONS

Although radio frequency emissions are usually harmless, there are still certain safety precautions you should follow whenever you are near high-power rf sources. Normally, electromagnetic radiation from transmission lines and antennas isn't strong enough to electrocute personnel. However, it may lead to other accidents and can compound injuries. Voltages may be induced into metal objects both above and below ground, such as wire guys, wire cable, hand rails, and ladders. If you come into contact with these objects, you may receive a shock or an rf burn. The shock can cause you to jump involuntarily, to fall into nearby equipment, or, when working aloft, to fall from the elevated work area. Take care to ensure that all transmission lines or antennas are de-energized before working on or near them.

When working aloft aboard ship, be sure to use a working aloft chit. This will ensure that all radiators, not only those on your own ship but also those nearby are secured while you are aloft.

ALWAYS obey rf radiation warning signs and keep a safe distance from radiating antennas. The six types of warning signs for rf radiation hazards are shown in figure 2-52.

The two primary safety concerns associated with rf fields are rf burns and injuries caused by dielectric heating.

RF BURNS

Close or direct contact with rf transmission lines or antennas may result in rf burns caused by induced voltages. These burns are usually deep, penetrating, third-degree burns. To heal properly, rf burns must heal from the inside toward the skin's surface. Do NOT take rf burns lightly. To prevent infection, you must give proper attention to ALL rf burns, including the small pinhole burns. ALWAYS seek treatment for any rf burn or shock and report the incident to your supervisor so appropriate action can be taken to correct the hazard.

DIELECTRIC HEATING

While the severity of rf burns may vary from minor to major, burns or other damage done by DIELECTRIC HEATING may result in long-term injury, or even death. Dielectric heating is the heating of an insulating material caused by placing it in a high-frequency electric field. The heat results from the rapid reversal of molecular polarization dielectric material.

When a human is in an rf field, the body acts as the dielectric. If the power in the rf field exceeds 10 milliwatts per centimeter, the individual will have a noticeable rise in body temperature. Basically, the body is "cooking" in the rf field. The vital organs of the body are highly susceptible to dielectric heating. The eyes are also highly susceptible to dielectric heating. Do NOT look directly into devices radiating rf energy. Remember, rf radiation can be dangerous. For your own safety, you must NOT stand directly in the path of rf radiating devices. 2-33