CS485 Sylabus

### Transmitting analog data using analog signals

• Analog data transmitted with analog signals

• 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

• Example a naive transmission

• "Talking":

• The atmosphere is suitable to carry audio waves....

• Sound waves can be transmitted naively:

• Intro to Modulation

• Problem:

• How can astronauts talk on the moon ???

 The moon does not have an atmosphere Sound wave is not suitable

• Solution:

• Radio waves can propagate through vacuum:

• We modulate the radio wave using a sound wave

• Then transmit the modulated radio wave (through vacuum)....

• What is "Modulation"

• Carrier wave:

• Carrier wave = a sine wave of a specific frequence and amplitude that propagates easily through the transmission medium

Example: carrier wave

• 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

• Amplitude modulation (AM)):

 the amplitude of the carrier wave is changed according to the input signal

Example:

• Frequency Modulation (FM)

• Frequency modulation (FM)):

 the frequency of the carrier wave is changed according to the input signal

Example:

• Phase Modulation (PM)

• 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:

• 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 :)