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Coast Guard Electronic Technician First Class

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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