Communications systems
Radio waves:
➔ Radio systems start with a sound passing into a microphone, the sound
signal is converted to radio signal and at the end, back to sound signal
➔ The information signal is transmitted with a carrier wave. Higher
frequency so shorter aerial required and different frequencies for
different stations.
➔
➔ Modulation is the variation of either amplitude or frequency of the carrier
wave. The modulated wave is the actual wave being transmitted. The
signal is present in either the changing amplitude or changing frequency
of the modulated wave.
➔ Advantages of modulation over direct:
◆ Shorter aerial required
◆ Longer transmission range
◆ Less attenuation
◆ Allows more than one station in a region
◆ Less distortion
,➔ Modulation is a way of sending signals of low frequency over long
distances without a huge loss of energy by the use of another wave of very
high frequency called a carrier wave. High frequency signals are more
directional and because high frequency waves have a small wavelength
there is less diffraction.
➔ Amplitude Modulation (AM):
◆ In amplitude modulation, the frequency of the modulated wave is
constant. The amplitude of the modulated wave is proportional to,
and in phase with, the
information signal.
◆ The amplitude of the signal
must be less than half of the
amplitude of the carrier
wave; otherwise the
variation in the amplitude at
the top will be confused
with the variation in the
amplitude at the bottom of
the wave.
◆ The variation in amplitude
of the carrier wave is the
measure of the
displacement (amplitude) of
the information signal.
◆ The rate at which the
carrier amplitude varies is equal to the frequency of the
information signal.
◆ The amplitude modulated wave consists of three components:
● Original carrier wave of frequency 𝑓𝑐and amplitude 𝐴𝑐
𝐴 𝑎
● A wave of frequency 𝑓𝑐 − 𝑓 𝑎
and amplitude
2
, 𝐴 𝑎
● A wave of frequency 𝑓𝑐 + 𝑓 𝑎
and amplitude
2
● The central frequency 𝑓𝑐 is that of the high-frequency carrier
wave
● The other two are known as sidebands
● The range of frequencies from the minimum to the maximum
in modulated carrier wave is called its bandwidth
(𝑓 𝑐
+ 𝑓 𝑎
) − (𝑓 𝑐
− 𝑓 𝑎) = 2𝑓 𝑎
➔ Frequency Modulation (FM):
◆ In FM, the frequency of the modulated wave varies with time.
Amplitude remains constant. Without any signal, the frequency of
the modulated wave is equal to the frequency of the carrier wave
Radio waves:
➔ Radio systems start with a sound passing into a microphone, the sound
signal is converted to radio signal and at the end, back to sound signal
➔ The information signal is transmitted with a carrier wave. Higher
frequency so shorter aerial required and different frequencies for
different stations.
➔
➔ Modulation is the variation of either amplitude or frequency of the carrier
wave. The modulated wave is the actual wave being transmitted. The
signal is present in either the changing amplitude or changing frequency
of the modulated wave.
➔ Advantages of modulation over direct:
◆ Shorter aerial required
◆ Longer transmission range
◆ Less attenuation
◆ Allows more than one station in a region
◆ Less distortion
,➔ Modulation is a way of sending signals of low frequency over long
distances without a huge loss of energy by the use of another wave of very
high frequency called a carrier wave. High frequency signals are more
directional and because high frequency waves have a small wavelength
there is less diffraction.
➔ Amplitude Modulation (AM):
◆ In amplitude modulation, the frequency of the modulated wave is
constant. The amplitude of the modulated wave is proportional to,
and in phase with, the
information signal.
◆ The amplitude of the signal
must be less than half of the
amplitude of the carrier
wave; otherwise the
variation in the amplitude at
the top will be confused
with the variation in the
amplitude at the bottom of
the wave.
◆ The variation in amplitude
of the carrier wave is the
measure of the
displacement (amplitude) of
the information signal.
◆ The rate at which the
carrier amplitude varies is equal to the frequency of the
information signal.
◆ The amplitude modulated wave consists of three components:
● Original carrier wave of frequency 𝑓𝑐and amplitude 𝐴𝑐
𝐴 𝑎
● A wave of frequency 𝑓𝑐 − 𝑓 𝑎
and amplitude
2
, 𝐴 𝑎
● A wave of frequency 𝑓𝑐 + 𝑓 𝑎
and amplitude
2
● The central frequency 𝑓𝑐 is that of the high-frequency carrier
wave
● The other two are known as sidebands
● The range of frequencies from the minimum to the maximum
in modulated carrier wave is called its bandwidth
(𝑓 𝑐
+ 𝑓 𝑎
) − (𝑓 𝑐
− 𝑓 𝑎) = 2𝑓 𝑎
➔ Frequency Modulation (FM):
◆ In FM, the frequency of the modulated wave varies with time.
Amplitude remains constant. Without any signal, the frequency of
the modulated wave is equal to the frequency of the carrier wave
