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modern physics > Communication System > Flashcards

Communication System Flashcards

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1
Q

distance covered by a antenna of highet ‘h’

A
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2
Q

distance covered between two antenna at the line of sight

A
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2
Q

popoulation covered by the antenna if population density is given

A
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3
Q
A

B

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4
Q

skywave frequceny range

A

2-30 MHz

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5
Q

space wave propagation frequency range

A

30-300 MHz

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6
Q

carrier waves has high/low frequency

A

high frequcny

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7
Q

carrier wave has large or small wavelength

A

small

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8
Q

size of antenna is directly proportional to?

A

wavelength

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9
Q

how to make a antenna size small

A

increase the frequency

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10
Q

effective power radiated is related to?

A
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11
Q

number of channels formula

A

max frequency available divided by bandwidth frequency(2f)

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12
Q

what changed in AM?

A

amplitdue changes as the nam e suggests amplitude modulation

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13
Q

max and mimimum amplitude of AM!?

A
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14
Q

modulation index formula

A
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15
Q

modulation index is less or more than 1

A

less than one

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16
Q

final wave frequency depends on which freuency?!

A

carrier frequency

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17
Q

final wave equation

A
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18
Q

final wave equation in terms of side carriers and side bands

and what does side bands and main carrier denoted by

A
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19
Q

upper side band frequency formula

A
20
Q

lower side band frequency formula

A
21
Q

bandwidth formula

A
22
Q
A
22
Q

power of wave in main carrier wave

A
23
Q

power of side bands

A
24
Q

which of the following quantities will be filtered out from the band pass filter?

A
25
Q

wavelength ranges of the different type of light waves

A
26
Q

The two basic modes of communication are

A

point-to-point and broadcast.

26
Q

bandwidth required by

speech signals
music
Video signals
TV signal

A

speech signals:- 2800 Hz (3100 Hz– 300 Hz)
music:- 20 kHz
Video signals:- 4.2 MHz
TV signal:- 6 MHz

27
Q

frequency range for speech signals

A

300 Hz to 3100 Hz

28
Q

audible range of frequencies extends from

A

audible range of frequencies extends from 20 Hz to 20 kHz.

29
Q

bandwidth required by

Coaxial cable
Optical communication
optical fiber

A

Coaxial cable:- 750 MHz.
Optical communication:- 1 THz to 1000 THz
optical fiber:- 100 GHz.

30
Q

just keep this table in mind

A
31
Q

The ionosphere is so-called because

and it extends from a height of

A

The ionosphere is so-called because of the presence of a large number of ions or charged articles. It extends from a height of 65 Km to about 400 km above the earth’s surface.

32
Q

The density of the atmosphere increases/decreases with height.

A

The density of atmosphere decreases with height.

33
Q

The ionospheric layer acts as a reflector for a certain range of frequencies:

A

3 to 30 MHz

34
Q

Electromagnetic waves of frequencies higher than _____ penetrate the ionosphere and escape.

A

Electromagnetic waves of frequencies higher than 30 MHz penetrate the ionosphere and escape.

35
Q

sky wave propagation is used by

A

short wave broadcast services.

36
Q

Ionisation occurs due to the

A

absorption of the ultraviolet and other high-energy radiation coming from the sun by air molecules.

37
Q

write something abt the ionization of ions due to solar radiation

A

The degree of ionization varies with the height. The density of the atmosphere decreases with height. At great heights the solar radiation is intense but there are few molecules to be ionized. Close to the earth, even though the molecular concentration is very high, the radiation intensity is low so the ionization is again low. However, at some intermediate heights, there occurs a peak of ionization density.

38
Q

Space waves are used for

A

line-of-sight (LOS) communication as well as satellite communication.

39
Q

At frequencies above 40 MHz communication is essentially limited

A

At frequencies above 40 MHz, communication is essentially limited to line-of-sight paths.

40
Q

power radiated from an antenna is proportional to

A

power radiated is proportional to (l/λ)^2

41
Q

why do we need high frequency transmission

A

For a good transmission, we need high powers and hence this also points out the need of using the high-frequency transmission.

42
Q

define detection of signals

A

Detection is the process of recovering the modulating signal from the modulated carrier wave.

43
Q

the process of detection of signals

A
44
Q

whats Facsimile

A

Facsimile (FAX)
It scans the contents of a document (as an image, not text) to create electronic signals. These signals are then sent to the destination (another FAX machine) in an orderly manner using telephone lines. At the destination, the signals are reconverted into a replica of the original document. Note that FAX provides an image of a static document unlike the image provided by television of objects that might be dynamic.

45
Q

Mobile telephones operate typically in the ____ range of frequencies

A

about 800-950 MHz (UHF)

modern physics (5 decks)

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