datacom_electronics Flashcards
A detectable physical quantity or impulse (as a voltage, or magnetic field strength) by which messages or information can be transmitted.
Signal
type of signal that can take only discrete values
digital
type of signal that can take values within a continuous range.
analog
s will have the same value as that of s at time t
after a time interval T has elapsed.
periodic signal
the instantaneous value of a signal in any time. For
electrical the unit is volts.
Amplitude
the number of repetitions per unit time.
Frequency
used to indicate a relative position and the unit used is the same as that for angles
Phase
refers to the amount of time, in seconds, a signal needs to complete one cycle.
period
refers to the number of periods in one second.
* F = 1/T and T = 1/F
frequency
symbol for amplitude (Sinusoids)
A
symbol for time (Sinusoids)
t
symbol for phase (Sinusoids)
ϕ
symbol for frequency (Sinusoids)
f
signal transmission used for digital signals
co-dec (encoder-decoder)
signal transmission used for analog signals
mo-dem (modulator-demodulator)
4 encoding and modulating techniques
Digital data with digital signals
Digital data with analog signals
Analog data with digital signals
Analog data with analog signals
the amount of data in bits per second that is transmitted
Data rate
the amount of time it takes for the transmitter to emit a bit (1/data rate).
Duration or length of a bit
the rate at which signal level is changed, expressed in units of baud.
Modulation rate
0 = low
1 = high
Non Return-to-Zero Level (NRZ-L)
0 = no transmission at the beginning of interval
1 = has transition at the beginning of interval
Non Return-to-Zero Inverted (NRZ-I)
0 = no line signal
1 = positive or negative level, with successive 1’s alternated
Bipolar - AMI
0 = positive or negative level with successive 0’s alternated
1 = no line signal
Pseudoternary
0 = transition from high to low at the center of an interval
1 = transition from low to high at the center of an interval
Manchester
0 = transition at the beginning of an interval
1 = no transition at the beginning of an interval
There is always a transition at the center of an interval
Differential Manchester
Modulating techniques of Digital Data with Analog Signal (3)
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
symbol for amplitude (ASK)
A
symbol for digital data input (ASK)
x
symbol for carrier frequency (ASK)
fc
symbol for carrier phase (ASK)
ϕc
formula for Amplitude Shift Keying (ASK)
s(t) = xA cos (2π fc t + ϕc )
formula for Frequency Shift Keying (FSK)
s(t) = xA cos (2π f1 t + ϕc ) binary 1
xA cos (2π f2 t + ϕc ) binary 0
formula for Phase Shift Keying (FSK)
s(t) = A cos (2π fc t + π ) binary 1
A cos (2π fc t ) binary 0
If the reference of a phase shift is with respect to the previous transmitted bit, it is termed as
differential PSK
is another form of angle-modulated digital modulation
Quadrature Phase Shift Keying (QPSK)
is another technique of converting digital data into analog signals that vary (or shift) both phase and amplitude of the carrier signal.
Quadrature Amplitude Modulation (QAM)
