Electromagnetic Interference Flashcards
Define Electromagnetic Interference
Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling or conduction
What are 3 natural sources of EMI?
Atmospheric
Solar
Galactic
How is EMI categorized?
Narrowband
Broadband
Define Narrowband EMI
Intended transmissions such as radio and TV stations or cell phones
Define Broadband EMI
Unintentional radio from sources such as electric power transmission lines
Define EME
Electromagnetic Environment
The resulting product of power and time distribution of the EM emission levels in the environment
Define ELectromagnetic Compatability EMC
The ability of electronic and electrical equipment to operate without degradation due to EMI
What are the 3 main types of EMC problems?
Emissions
Immunity
Overvoltage/Grounding
Define Emissions as it relates to EMC
Meethods that prevent EM emissinos from causing faulty operation in other equipment
Define Immunity as it relates to EMC
Methods that enable equipment to operate stably and faultylessly even if it recieves EMI
Define Overvoltage/Grounding as it relates to EMC
Protects against excess voltages due to lightning, inductance, power accidents. Includes grounding
What are 3 coupling mechanisms?
Antenna to Antenna
Antenna to Cable
Antenna to equipment
Cable to cable
Hull to Antenna
Whats the cause of antenna to antenna coupling?
Poor isolation between transmit and recieve antenna
What causes Antenna to Cable coupling?
Cables penetrating hull become crude forms of antenna
What is the cause of Antenna to Equipment coupling?
Hazard mounted topside or within close proximity of radiating antenna
What causes cable to cable coupling?
Coupling from cable carrying high currents into cable connected to sensitive equipment.
What causes hull to antenna coupling
Induced currents in the ship’s hull will be radiated.
Rusty connections and other nonlinear elements connected to the hull may change the frequency.
What are supression techniques for Antenna to Antenna coupling?
Relocate antenna
Use null steering or directional antennas
Limit number of antennas
Better filtering
How do we suppress Antenna to Cable coupling?
Re-route cables
Use double sheilded cables
Place cables in conduit
How do we supress Antenna to Equipment coupling?
Relocate equipment
Add RFI gaskets
Protective casings
Internal EMI supression
How do we suppress cable to cable coupling
Segregate cables
Add shielding
Re-route cables
Filter out conducted EMI
How do we suppress Hull to Antenna coupling
Eliminate rusty bolts and other non-linearities
Replace metallic guardrails with non conducting material such as rope
What do we use for shielding?
Metal barrier
How does a Faraday cage work?
If the current is zero, the electric field inside the metal is zero. Ground the metal cage.
