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ET1 EOC U1 L5
Coast Guard Electronic Technician First Class
| Question | Answer |
|---|---|
| What are the three types of EMI? | Man-made, natural, and Inherent. |
| What is EMI? | Electro-Magnetic Iterference. |
| What can EMI be classified as? | Narrowband or Broadband. |
| Man-made interference impedes the _____ and ____ of electrical and electronic equipment. | reliable and efficient use |
| What are some examples of broadband transient EMI? | Function switches, motor starters, thermostats, and timer units. |
| What are some examples of broadband intermittent EMI? | Electronic computers, motor speed controls, poor ground connections, and welding equipment. |
| What are some examples of broadband continuous EMI? | Commutation noise, electronic typerwriters, ignition systems, arc and vapor lamps, pulse generators, RADAR modulators, and sliding contacts. |
| What are some examples of narrowband intermittent EMI? | Doppler shift RADAR, radio transmitters, and electronic computers. |
| What are some examples of narrowband continuous EMI? | Power line hum and receiver local oscillators. |
| What is narrowband interference? | Narrowband interference consists of a single frequency or a narrow band of frequencies that occupies little space in the total receiver passband. |
| What is one way to deal with interferance from a narrowband signal? | Tune the reciver away from the interfing narrowband signal. |
| What is broadband interference? | Broadband interference occupies a relatively large part of the radio frequency spectrum. |
| What can cause communication transmitters to produce spurious emissions? | Overdriven amplifiers, frequency multiplier stages, sideband splatter, modulator noise, and transmitter intermodulation or cross modulation. |
| What can cause radar transmitters to produce spurious emisions? | Arcing in PA stage, waveguide rotary joint or antenna. |
| Make-brake contactors, such as _____, cause sharp changes in the current waveform which may produce severe interference over a wide frequency band. | swithches and relays |
| What is the most common source of EMI? | Electrical motors and genterators. |
| DC motors or generators may cause EMI by ___. | arcing from brushes to commutator segments |
| AC motors or generators may cause EMI by ____. | arcing from brushes to slip rings |
| Rotating machinery may induce interference into nearby electronic equipment from ___. | the high energy magnetic fields |
| What is present to some degree in the out put of all DC generators. | Ripple. |
| What causes slot harmonics in electric motors? | Slot harmonics are the result of a lack of uniformity in the magnetic field caused by the effect of the armature slots on the distribution of the magnetic flux. |
| What can be a source of EMI on gasoline engines. | Ignition systems. |
| Igniters for jet engines that use high voltage and current can cause what _______. | severe interference. |
| The steep waveform associated with the operations of flourescent, mercury, sodium, and vapor lamps can cause _______. | broadband interference. |
| What natural interference causes impulses of high intensity, occuring intermittentlly? | local thunderstorms. |
| What is referred to as atmospheric noise or static? | Natural Interference. |
| What natural interference causes a steady rattling or crackling? | distant thunderstorms. |
| What is a continuous noise caused by the impact of charged particles against an antenna? | Precipitaion static. |
| A steady hiss type of static observed at high frequencies apparently haveing an ______. | intersteller origin. |
| A certain amount of interference inherent in receiving equipment caused by ______ of electrons in the circuit resistance. | thermal agitaion |
| What are the two ways that interference is transferred from an interfering source to the affected equipment? | Conduction and radiation. |
| What is conducted EMI? | The transfer of undesired energy through conductors betwen a source of interference and a susceptible device. |
| What are the most common paths for conducting current? | Power supply cables, control and accessory cables, grounding systems, and transmission lines. |
| What do the type of circuit, frequencies involved, power level, and amount of capacitive and inductive coupling between parts of the circuit have in common? | All have bearing on the generation of the interference that can be conducted from one piece of equipment to another. |
| What can reduce the amount of interference conducted from a piece of equipment and the degree of susceptibility of your equipment to this interference? | The care taken with lead dress, filtering, and shielding. |
| What is radiated EMI? | Any signal transferred through space by an electromagnetic field. |
| An electromagnetic field is generated whenever current flows in a ____. | conductor |
| What determines the strength of EMI's radiated field? | Amount of current flow in the conductor, efficiency of the conductor as an antenna, and frequency of the current waveform. |
| What is the best way to suppress radiated EMI? | Shielding the EMI source. |
| What types of rotating machinary produce EMI? | Rotary inverter, dynamotor, motors, and generators. |
| How can rotating machinary produce EMI? | Through arcing, induction, ripple and slot harmonics. |
| How does arcing occur in DC motors and generators? | By brushes sweeping over commutaor segments. |
| What is induction EMI? | Inerference voltage coused by the magnetic field associated with rotating electrical machines. |
| What type of EMI is present in the output of all DC generators? | Ripple. |
| What is a common source of slot harmonics? | Ships generators. |
| What are some examples of Spurious Emissions from transmitters? | Broadband emissions, spurious sidebands (splatter), harmonic radiation, parasitic oscillation, spurious outputs, transmitter noise, cross and intermodulation |
| What causes broadband emissions from a transmitter? | arcing either in the transmission line, tuner/coupler, transmitter, or in the rigging and deck equipment of the ship. |
| What can help eliminate broadband emissions? | Make the entire topside area of the ship a single conducting structure. |
| What causes spurios sidebands (splatter)? | Improperly tuned circuits, over modulation, or faulty equipment. |
| What causes Harmonic Radiation? | Nonlinearity of the power output stage. |
| How many db must the second harmonic be below the fundamental. | 60 db |
| Third and higher order harmonics must be at least ___ below the fundamental. | 80 db |
| What causes parasitic oscillations? | When a circuit is self excited. |
| What causes spurious outputs? | Non-linearity of the mixer or harmonics of master oscillator. |
| Where is transmitter noise generated? | Various RF stages. |
| What is cross modulation. | The transfer of modulation from one carrier to another. |
| What is intermodulation? | The generation of numerous new frequencies from two or more original signals. |
| What are the three ways that undesired signals intrude on a selected or desired signals? | Linear intrusion, Nonlinear intrusion, intrusion through ports not intended as a signal input. |
| What is linear intrusion? | Unwanted inputs with a spectrum centered at, or near, the tuned frequency of the RF. |
| What does a blanking device do? | Reduce effects of interference by cutting off or blanking the susceptible equipment during the time of interference. |
| What is co-channel interference? | Interference that takes place in communication systems that are assigned the same, or nearly the same, carrier frequency. |
| What is adjacent channel interference? | Adjacent channel interference occurs when some sidebands (no the center frequency or carrier of an undesired signal) are withen the receiver bandpass. |
| What is intermediate frequency interference? | The penetration of unwanted signals that are centered at any pass frequency within the receiver. |
| What is non-linear intrusion? | When a strong unwanted signal penetrates the input filter circuits and encounters a nonlinear element such as the mixerof an overloaded RF amplifier stage. |
| Interference signals caused by hull nonlinearities are directly related to? | The number and power level of transmitters and antennas being used at the same time. |
| A corroded joint or oxidised fastning is in the path of current flow rectification occurs. What is this effect? | Rusty bolt effect. |
| What are the different types of corrosion? | Galvanic, fatigue, crevise, stress, and welding. |
| What is the process called when two dissimeler metels are joined by the same corroding medium and elctrochemical corrosion occurs? | Galvanic corrosion. |
| What type of corrosion happens when a metal's protective film is broken down by bending or vibration? | Fatigue corrosion. |
| What causes crevice corrosion? | When corrosive solutions are retained in crevices. |
| What is the most difficult form of corrosion to predict? | Stress corrosion. |
| Welding corrosion couses what? | Variations in grain size. |
| What is Heterodyning? | The mixing of two frequencies to create a new frequency. |
| What happens when a frequency is distorted in any way? | Harmonics are created. |
| Sources of hull generated interference are? | Loose metalic objects, corroded stations and metalic life lines, rusty anchor chains, metalic cables, and mast items. |
| The level of hull-generated interference signals is determined by: | Transmitter output power, efficiency of the nonlinear element as a rectifier, coupling and amount of shielding between transmitter and the nonlinear element, The physical size and physical properties. |
| What metal is inherently nonlinear and produces intermodulation products? | Steel. |
| What is the best way to prevent nonlinear EMI? | Make the topside of the ship a single conductor. |
| Where can RF leakage occur in a RADAR system? | At any waveguide or coaxial cable joint. |
| What can prevent RF leakage in a RADAR system? | Wave should be firmly connected, bolts should be outside high intensity RF area, and the gasket should be between boltholes and RF area. |
| What can cause arcing in waveguides? | Foreign objects and a sharp bend in the waveguide. |
| What are the signs of arcing in RADAR waveguide? | Heat and high VSWR. |
| What may cause arcing in a RADAR rotary joint? | Dirt, ware, and misalignment. |
| What is the best way to detect arcing in mast cables? | At night when the RADAR is operating. |
| What is the best way to prevent arcing in mast cables? | Good housekeeping. |
| What is the most effective way to prevent PRF overload in a receiver? | Locate all reciever antennas out of the main beam of a RADAR. |
| What are "running raddits"? | A serias of moving dots on a RADAR display caused by several of the same type of RADAR operating within a few miles of each other. |
| What are some methods of bonding? | Welding, brazing and pressure connections. |
| What is bonding? | The process of providing a low impedance union between two metallic conductors. |
| What is Equipotential Ground Plane? | A large conducting area which offers little impedance to current flow. |
| What is direct bonding? | Metal-to-metal contact through welding of brazing. |
| What is indirect bonding? | The use of a jumper or bolts between two metal items. |
| What are the two main purposes of shielding? | Confine EMI within a specific region, and to prevent EMI from entering a specific region. |
Created by:
CG ET1
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