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TM355 > B1P1 - Channels for communication > Flashcards

B1P1 - Channels for communication Flashcards

1
Q

absorption

A

where EMR is attenuated from passing through a medium;

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2
Q

amplitude

A

the maximum absolute value of a periodic signal;

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3
Q

analogue signal

A

a signal that can take any value within a continuous range;

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4
Q

attenuation

A

reduction in the power of a signal, e.g. through absorption;

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5
Q

attenuation coefficient

A

how much a signal is attenuated when passing through a specific medium; units are dB m^-1;

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6
Q

bandwidth (B)

A

the amount of spectrum occupied by the signal spectrum: B = f_max - f_min;

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7
Q

beamwidth

A

the cone angle containing the antenna’s radiation above maxPower - 3dB;

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8
Q

antenna

A

EMR <==> current

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9
Q

bipolar signal

A

a signal that uses positive and negative voltages to rep data 1s and 0s;

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10
Q

Carson’s rule (formula)

A

gives bandwidth of a freq-modulated signal:

B_fm = 2 * (delta_f + f_mod) = 2 * (1 + beta) * f_mod

…where
delta_f = f_max - f_min
f_mod = is the max(mod_freq)
beta = mod_index;

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11
Q

cladding

A

the layer (with a lower refractive index) surrounding the central core of an optical fibre;

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12
Q

combiner

A

a device taking input signals from 2+ optical fibres and merging them into a single output;

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13
Q

core

A

the innermost part (with a higher refractive index) of an optical fibre;

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14
Q

crosstalk

A

where neighbouring copper cables carrying different signals interfere with each other;

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15
Q

current

A

transfers energy in a cable through the movement of electrons;

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16
Q

decade

A

a range of values covering a ten-fold increase, e.g. 20 to 200;

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17
Q

decibel

A

an alternative rep of = power1/power2 = G_dB:

G_dB = 10 * log_10(power1 / power2);

power1/power2 = 10^(G_dB/10);

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18
Q

demultiplexing

A

converting a multiplexed signal back to the original set of signals;

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19
Q

dielectric (insulating) loss

A

where the signal energy is dissipated through the material separating the copper cable’s conductors;

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20
Q

diffraction

A

where EMR spreads / bends / wraps round when passing through a gap or by a sharp corner;

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21
Q

digital signal

A

can take one of a set of discrete values;

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22
Q

dipole

A

an antenna consisting of two straight conductors in a line:

———-<>———-;

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23
Q

directional coupler

A

combines or splits optical signals;

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24
Q

dispersion

A

where the signal is distorted due to there being light of varying frequencies and speeds in the optical fibre;

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25
Q

distributed amplifier

A

a device which laser-zaps an optical fibre’s full transmission path to amplify the signal;

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26
Q

envelope

A

the shape of an amplitude modulated signal;

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27
Q

erbium-doped fibre amplifier (EDFA)

A

where erbium atoms are added to a section of the optical fibre and then lazer-zapped to amplify the signal;

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28
Q

far field

A

all space outwith a few wavelengths from the antenna and where 1/d^2 law applies;

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29
Q

filtering

A

where only a subset of frequencies are allowed to pass through;

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30
Q

frequency deviation

A

for a freq-modulated signal, the max. difference between mod-frequency and carrier-frequency;

31
Q

frequency modulation

A

where the mod-wave inflects the carrier-wave’s frequency to rep symbols;

32
Q

graded-index fibre

A

where the refractive index changes smoothly from high in the core to low in the cladding;

33
Q

inverse fourth-power law

A

1 / (d^4);

34
Q

inverse square law

A

1 / (d^2);

35
Q

ionosphere

A

a layer of the atmosphere containing molecules with a net charge [i.e. #protons != #eletrons];

36
Q

isotropic

A

an antenna that has a 3D spherical radiation envelope;

37
Q

light-emitting diode (LED)

A

current ==> EMR;

38
Q

logarithmic scale

A

where each tick on the scale is the previous tick multiplied by n, where n is the base of the log (typically 2, 10, or e);

39
Q

modulating signal

A

the signal inflecting the carrier-signal to rep symbols;

40
Q

modulation

A

where a carrier-signal is inflected by a mod-signal to rep symbols;

41
Q

modulation index

A

the ratio of frequency deviation to max frequency in the mod-signal:

beta = delta_freq / freq_max;

42
Q

multimode fibre

A

where the core diameter is large compared to wavelength, allowing light to take many paths;

43
Q

multipath reception

A

where EMR signals are received via 2+ paths;

44
Q

multiplexing

A

where 2+ signals are transmitted through a single medium;

45
Q

near field

A

all space within a few wavelengths of the antenna and where 1/d^2 law does not apply;

46
Q

omnidirectional

A

an antenna that has a flat 2D disc-like radiation envelope;

47
Q

passband

A

the frequencies that a filter allows to pass through;

48
Q

period

A

T = 1 / freq.

49
Q

periodic signal

A

a signal that repeats at regular time intervals;

50
Q

phase

A

from the interval [0, 2pi), the amount a periodic signal has been shifted along the horizontal axis;

51
Q

phase modulation (PM)

A

where the phases of the mod-wave and carrier-wave differ by for example pi, and each are switched on and off to rep symbols;

52
Q

photodiode

A

EMR ==> current

53
Q

polarisation mode distortion

A

where some light zig-zags and some zooms in narrow fibres thereby distrorting the signal;

54
Q

pulse spreading

A

where the sharp states of a digital signal diffuse in transmission;

[ |’’‘| ==> _/’’‘_ ]

55
Q

quantising

A

where, at regular time intervals, an analogue signal is rounded to the nearest value from an value-alphabet;

56
Q

refractive index

A

refractive_index = c / v_medium;

57
Q

regenerator

A

a midway device that relays a corrected version of the received signal;

58
Q

repeater

A

a midway device that relays just an amped up version of the received signal;

59
Q

resistance

A

how difficult it is for an electric current to pass through a conductor;

60
Q

resolution

A

for quantising, the number of discrete levels chosen to rep an analogue signal: bits_to_rep_level = log_2(numLevels);

61
Q

(frequency) response

A

how sensitive an antenna is to frequencies at / around its tuned frequency;

62
Q

sampling

A

measuring an analogue signal at regular time intervals;

63
Q

selectivity

A

how well an antenna can reject signals outside its passband;

64
Q

single-mode fibre

A

where light can travel only one way through due to the fibre’s narrow core;

65
Q

sinusoid

A

a periodic signal with the general form v(t) = A * sin((2pif*t) + phi);

66
Q

sky wave

A

where the ionosphere reflects / refracts EMR back to Earth;

67
Q

step-index fibre

A

where there is an abrupt change of refractive index between core and cladding;

68
Q

threshold detection

A

where a received binary signal value is tested against the predefined value separating a data 1 from a data 0;

69
Q

total internal reflection

A

where light reflects at the boundary between two media with different refractive indices;

70
Q

voltage

A

volt = power / current;

71
Q

voltage-controlled oscillator (VCO)

A

voltage (signal) ==> frequency;

72
Q

waveform

A

a periodic signal’s shape in time domain;

73
Q

wavelength division multiplexing (WDM)

A

where multiple signals of different wavelengths share a single optical fibre;

TM355 (10 decks)

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