How does phase modulation differ from frequency modulation in AC signal transmission?
1 Answer
Phase modulation (PM) and frequency modulation (FM) are both methods used for modulating analog signals onto a carrier waveform in the context of communication systems. While they are related and share some similarities, they differ primarily in how they encode information onto the carrier signal.
Frequency Modulation (FM):
In frequency modulation, the instantaneous frequency of the carrier signal is varied according to the amplitude of the modulating signal (the signal containing the information to be transmitted). When the amplitude of the modulating signal increases, the frequency of the carrier signal also increases, and when the amplitude decreases, the frequency decreases. This results in a signal with varying frequency and a relatively constant amplitude.
Mathematically, the instantaneous frequency of an FM signal can be described as:
(
)
=
+
⋅
(
)
f(t)=f
c
+k
f
⋅m(t)
Where:
(
)
f(t) is the instantaneous frequency of the FM signal at time
t.
f
c
is the carrier frequency.
k
f
is the frequency modulation sensitivity (constant).
(
)
m(t) is the modulating signal (the signal containing the information).
Phase Modulation (PM):
In phase modulation, the phase of the carrier signal is varied according to the amplitude of the modulating signal. As the amplitude of the modulating signal changes, the phase of the carrier signal changes accordingly. This leads to a signal with varying phase and constant amplitude.
Mathematically, the instantaneous phase of a PM signal can be described as:
(
)
=
+
⋅
(
)
ϕ(t)=ϕ
c
+k
p
⋅m(t)
Where:
(
)
ϕ(t) is the instantaneous phase of the PM signal at time
t.
ϕ
c
is the carrier phase.
k
p
is the phase modulation sensitivity (constant).
(
)
m(t) is the modulating signal (the signal containing the information).
Comparison:
The key difference between FM and PM lies in how they modulate the carrier signal:
In FM, the frequency of the carrier signal changes in response to the amplitude variations of the modulating signal.
In PM, the phase of the carrier signal changes in response to the amplitude variations of the modulating signal.
While both FM and PM are used in various communication systems, they have different characteristics and advantages. FM is often used in applications where noise immunity is important, such as in radio broadcasting, because changes in frequency are less susceptible to amplitude fluctuations caused by noise. PM, on the other hand, can be more bandwidth-efficient and is used in applications like phase-shift keying (PSK) modulation schemes in digital
Frequency Modulation (FM):
In frequency modulation, the instantaneous frequency of the carrier signal is varied according to the amplitude of the modulating signal (the signal containing the information to be transmitted). When the amplitude of the modulating signal increases, the frequency of the carrier signal also increases, and when the amplitude decreases, the frequency decreases. This results in a signal with varying frequency and a relatively constant amplitude.
Mathematically, the instantaneous frequency of an FM signal can be described as:
(
)
=
+
⋅
(
)
f(t)=f
c
+k
f
⋅m(t)
Where:
(
)
f(t) is the instantaneous frequency of the FM signal at time
t.
f
c
is the carrier frequency.
k
f
is the frequency modulation sensitivity (constant).
(
)
m(t) is the modulating signal (the signal containing the information).
Phase Modulation (PM):
In phase modulation, the phase of the carrier signal is varied according to the amplitude of the modulating signal. As the amplitude of the modulating signal changes, the phase of the carrier signal changes accordingly. This leads to a signal with varying phase and constant amplitude.
Mathematically, the instantaneous phase of a PM signal can be described as:
(
)
=
+
⋅
(
)
ϕ(t)=ϕ
c
+k
p
⋅m(t)
Where:
(
)
ϕ(t) is the instantaneous phase of the PM signal at time
t.
ϕ
c
is the carrier phase.
k
p
is the phase modulation sensitivity (constant).
(
)
m(t) is the modulating signal (the signal containing the information).
Comparison:
The key difference between FM and PM lies in how they modulate the carrier signal:
In FM, the frequency of the carrier signal changes in response to the amplitude variations of the modulating signal.
In PM, the phase of the carrier signal changes in response to the amplitude variations of the modulating signal.
While both FM and PM are used in various communication systems, they have different characteristics and advantages. FM is often used in applications where noise immunity is important, such as in radio broadcasting, because changes in frequency are less susceptible to amplitude fluctuations caused by noise. PM, on the other hand, can be more bandwidth-efficient and is used in applications like phase-shift keying (PSK) modulation schemes in digital