Transmission Fundamentals
Chapter 2

Electromagnetic Signal
Function of time
Can also be expressed as a function of
frequency
Signal consists of components of different
frequencies

Time-Domain Concepts
Analog signal - signal intensity varies in a smooth
fashion over time
No breaks or discontinuities in the signal
Digital signal - signal intensity maintains a
constant level for some period of time and then
changes to another constant level
Periodic signal - analog or digital signal pattern
that repeats over time
s
(
t
+
T
) =
s
(
t
) -¥<
t
< +¥
where
T
is the period of the signal

Analog and Digital Waveforms

Time-Domain Concepts
Aperiodic signal
- analog or digital signal pattern
that doesn't repeat over time
Periodic signal-
analog or digital signal pattern
which repeats over time
Peak amplitude (
A
)
- maximum value or strength
of the signal over time; typically measured in volts
Frequency (
f
)
Rate, in cycles per second, or Hertz (Hz) at which the
signal repeats

Time-Domain Concepts
Period (
T
) - amount of time it takes for one
repetition of the signal
T
= 1/
f
Phase (
) - measure of the relative position in time
within a single period of a signal
Wavelength (
)
- distance occupied by a single
cycle of the signal
Or, the distance between two points of corresponding
phase of two consecutive cycles

Sine Wave Parameters
General sine wave
s
(
t
) =
A
sin(2
ft
+
)
Figure 2.3 shows the effect of varying each of the
three parameters
(a)
A
= 1,
f
= 1 Hz,
= 0; thus
T
= 1s
(b) Reduced peak amplitude;
A
=0.5
(c) Increased frequency;
f
= 2, thus
T
= ½
(d) Phase shift;
=
/4 radians (45 degrees)
note: 2
radians = 360° = 1 period

Sine Wave Parameters

Time vs. Distance
When the horizontal axis is
time
, as in Figure 2.3,
graphs display the value of a signal at a given
point in
space
as a function of
time
With the horizontal axis in
space
, graphs display
the value of a signal at a given point in
time
as a
function of
distance
At a particular instant of time, the intensity of the signal
varies as a function of distance from the source

Frequency-Domain Concepts
Fundamental frequency - when all frequency
components of a signal are integer multiples of one
frequency, it’s referred to as the fundamental frequency
Spectrum - range of frequencies that a signal contains
Absolute bandwidth - width of the spectrum of a signal
Effective bandwidth (or just bandwidth) - narrow band
of frequencies that most of the signal’s energy is
contained in

Frequency-Domain Concepts
Any electromagnetic signal can be shown to

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- Summer '16
- hasnain
- Frequency, Wireless-communication-and-net, digital transmission, wireless transmission