ƒ Effect Of Noise on ASK
o ASK is highly susceptible to noise
interference
o NOISE:
Unintentional voltages introduced onto a line by various sources such
as
Heat or Electromagnetic Radiation from other sources
o These unintentional voltages combine with
signal to change the amplitude
o A 1 can be changed to 0 and a 0 to a 1
o ASK relies solely on Amplitude for
recognition
o Noise usually affects the amplitude,
therefore ASK is the modulating method,
that
is most affected by Noise
¾ On-Off Keying (OOK)
o A popular ASK Technique
o In OOK, one of the bit values is
represented by no voltage
o The advantage is the reduction in the
amount of energy required to
transmit
Information
¾ Bandwidth for ASK
o Bandwidth
of a signal
is total range
of frequencies occupied
by that
signal
o When we decompose an ASK modulated
signal, we get a spectrum of
many
simple frequencies
o The most significant ones are those
b/w, fc-Nbaud/2 and fc+Nbaud /2
with
carrier frequency fc at the middle
 |
o BW=(1+d) * Nbaud
o BW = Bandwidth
o Nbaud= Baud Rate
o d= factor related to condition of line
(min.value = 0)
Example
5.8
|
Find minimum
bandwidth required for an ASK signal TX at 2000 bps. TX. Mode is half
duplex
Solution:
-In ASK, Baud
Rate= Bit Rate
-Therefore,
Baud Rate = 2000
-Also ASK
requires a minimum bandwidth equal to its Baud Rate
|
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