- 2 ways to
transmit
analog data using
analog signals:
- If the transmission medium
is
suitable
(i.e., it can
carry the transmitted signals),
then:
- transmit the signal...
- If the transmission medium
is
not suitable
(i.e., it does not
carry the transmitted signals),
then:
- Modulate (super-impose)
the
signal on a
carrier signal
- Transmit the modulated signal
- Modulate (super-impose)
the
signal on a
carrier signal
- If the transmission medium
is
suitable
(i.e., it can
carry the transmitted signals),
then:
- "Talking":
- The atmosphere is
suitable to
carry
audio waves....
- Sound waves can be
transmitted
naively:
- The atmosphere is
suitable to
carry
audio waves....
- Problem:
- How can
astronauts
talk on the moon ???
- The moon does
not
have an atmosphere
- Sound wave is not suitable
- The moon does
not
have an atmosphere
- How can
astronauts
talk on the moon ???
- Solution:
- Radio waves
can propagate through
vacuum:
- We modulate the
radio wave
using
a sound wave
- Then transmit the modulated radio wave (through vacuum)....
- Radio waves
can propagate through
vacuum:
- Carrier wave:
- Carrier wave =
a sine wave of a
specific
frequence and
amplitude that
propagates easily
through the transmission
medium
Example: carrier wave
- Carrier wave =
a sine wave of a
specific
frequence and
amplitude that
propagates easily
through the transmission
medium
- Modulation:
- Modulation = change a carrier wave using some (input) signal
- What can you
change in
the carrier wave:
- The amplitude of the carrier wave (= Amplitude Modulation (AM)
- The frequency of the carrier wave (= Frequency Modulation (FM)
- The phase of the carrier wave (= Phase Modulation (PM)
- Amplitude modulation
(AM)):
- the amplitude of the carrier wave is changed according to the input signal
Example:
- Frequency modulation
(FM)):
- the frequency of the carrier wave is changed according to the input signal
Example:
- Phase modulation
(PM)):
- the phase of the carrier wave is changed according to the input signal
- The phase of
a wave:
- The phase of
a sine wave is the
amount of shift:
- The phase of
a sine wave is the
amount of shift:
- In PM, you change the
instantaneous phase
of the carrier signal.
- This is very hard to detect, even for electronics - let alone humans !!!
I will not try to draw a continuous phase shifted signal.....
It's too hard :)