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Electromagnetism > Electromagnetic Interference > Flashcards

Electromagnetic Interference Flashcards

1
Q

Define Electromagnetic Interference

A

Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling or conduction

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2
Q

What are 3 natural sources of EMI?

A

Atmospheric
Solar
Galactic

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3
Q

How is EMI categorized?

A

Narrowband

Broadband

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4
Q

Define Narrowband EMI

A

Intended transmissions such as radio and TV stations or cell phones

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5
Q

Define Broadband EMI

A

Unintentional radio from sources such as electric power transmission lines

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6
Q

Define EME

A

Electromagnetic Environment

The resulting product of power and time distribution of the EM emission levels in the environment

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7
Q

Define ELectromagnetic Compatability EMC

A

The ability of electronic and electrical equipment to operate without degradation due to EMI

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8
Q

What are the 3 main types of EMC problems?

A

Emissions
Immunity
Overvoltage/Grounding

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9
Q

Define Emissions as it relates to EMC

A

Meethods that prevent EM emissinos from causing faulty operation in other equipment

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10
Q

Define Immunity as it relates to EMC

A

Methods that enable equipment to operate stably and faultylessly even if it recieves EMI

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11
Q

Define Overvoltage/Grounding as it relates to EMC

A

Protects against excess voltages due to lightning, inductance, power accidents. Includes grounding

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12
Q

What are 3 coupling mechanisms?

A

Antenna to Antenna
Antenna to Cable
Antenna to equipment
Cable to cable
Hull to Antenna

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13
Q

Whats the cause of antenna to antenna coupling?

A

Poor isolation between transmit and recieve antenna

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14
Q

What causes Antenna to Cable coupling?

A

Cables penetrating hull become crude forms of antenna

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15
Q

What is the cause of Antenna to Equipment coupling?

A

Hazard mounted topside or within close proximity of radiating antenna

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16
Q

What causes cable to cable coupling?

A

Coupling from cable carrying high currents into cable connected to sensitive equipment.

17
Q

What causes hull to antenna coupling

A

Induced currents in the ship’s hull will be radiated.

Rusty connections and other nonlinear elements connected to the hull may change the frequency.

18
Q

What are supression techniques for Antenna to Antenna coupling?

A

Relocate antenna
Use null steering or directional antennas
Limit number of antennas
Better filtering

19
Q

How do we suppress Antenna to Cable coupling?

A

Re-route cables
Use double sheilded cables
Place cables in conduit

20
Q

How do we supress Antenna to Equipment coupling?

A

Relocate equipment
Add RFI gaskets
Protective casings
Internal EMI supression

21
Q

How do we suppress cable to cable coupling

A

Segregate cables
Add shielding
Re-route cables
Filter out conducted EMI

22
Q

How do we suppress Hull to Antenna coupling

A

Eliminate rusty bolts and other non-linearities

Replace metallic guardrails with non conducting material such as rope

23
Q

What do we use for shielding?

A

Metal barrier

24
Q

How does a Faraday cage work?

A

If the current is zero, the electric field inside the metal is zero. Ground the metal cage.

25
Q

How are cabinets protected from EMI?

A

Copper gasketing
Finger stock
Grounded cable panel

26
Q

How can the ship reduce its radar cross section?

A

Radar Absorbing Material (RAM)

27
Q

What are 4 categories of cabling as it pertains to EMI?

A

Active (A) - High level of voltage or current
Susceptible (S) Low level
Special Handling (X, M, PF) - radio transceiver, etc.
Passive Cabling - all other cables

28
Q

What is a ground loop?

A

When two grounds are connected from the same piece of equipment and they are not perfect grounds, they can create a potential difference between them in the ground. Also can be by two separate pieces of equipment.

29
Q

Describe Single Point Ground

A

No connection between cabineet and circuit. They are each grounded separately to the same ground.

30
Q

Describe Floating Signal Ground

A

The circuits and the cabinets are not connected and are grounded to their own separate grounds which do not connect.

31
Q

Describe Zonal Grounding

A

Ground within a ground within a ground

32
Q

What is a space wave

A
33
Q

Describe a Sky Wave

A
34
Q

Describe a Ground Wave

A

Electromagnetism (2 decks)

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