ELECTROMAGNETIC RADIATION

3-40 of a desired signal intermodulates with the carrier of an undesired signal. Extremely strong, off-frequency signals may even burn out the sensitive front-end stages of a receiver. Emi also can degrade overall receiver performance in a less noticeable way. It does this by desensitizing the receiver front end. The noise level is raised and effectively lowers the signal to noise ratio and thus the sensitivity. This causes a decrease in desired signal amplification. For these reasons, shipboard receive systems are designed to include protective circuitry between the antenna and receiver to filter out off-frequency signals. This prevents or limits interference, desensitization, or burnout. Depending upon the system, these protective devices may include filters, multicouplers, preselectors, and so forth. These devices can minimize interference caused by inadequate frequency separation or poor physical isolation between transmit and receive antennas. Q35. What is the purpose of QMCS? Q36. What is emi? Q37. What are the two emi transmission methods? ELECTROMAGNETIC RADIATION Radio-frequency (rf) transmitting systems with high-power transmitting tubes and high-gain antennas have increased the possibility of injury to personnel working in the vicinity. An electromagnetic radiation hazard exists when electronic equipment generates a strong enough electromagnetic field to fall in a category listed below: � Causes harmful or injurious effects to humans and wildlife � Induces or otherwise couples currents and/or voltages of magnitudes large enough to initiate electroexplosive devices or other sensitive explosive components of weapons systems, ordnance, or other explosive devices � Creates sparks large enough to ignite flammable mixtures or materials that must be handled in the affected areas These hazardous situations can be caused by a transmitter or antenna installation. These generate electromagnetic radiation in the vicinity of personnel, ordnance, or fueling operations in excess of established safe levels. Sometimes the existing electromagnetic radiation levels increase to a hazardous level. When personnel, ordnance, or fueling evolutions are located in an area that can be illuminated by electromagnetic radiation, hazardous situations may occur. Electromagnetic radiation is hazardous to personnel in two ways. It can cause rf burns; and it can cause biological, thermal, and neurological effects to personnel (RADHAZ). Because of the differences in characteristics and safety precautions required for each of the two types, they will be discussed separately. An rf burn hazard is a hazardous condition caused by the existence of radio frequency (rf) voltages in places where they are not intended to be. Any ship with high-power hf transmitters is susceptible. Potentially hazardous voltages have been found in many areas. Some of these areas are lifelines, vertical ladders, ASROC launchers, gun mounts, rigging for underway replenishment, and boat davits. Another of these areas is on aircraft tied down on carrier and helicopter flight decks. Whether or not an induced voltage creates an rf burn hazard depends on whether personnel will come into contact with the object being energized. Generally, only the voltage between an object and the deck is important. The rf burn occurs when a person comes into contact with a source of rf voltage in a