communication system introduction Am broad casting Superhetrodyne Receiver Spectrum domain

1. AM-Radio

2. - Direct (ex. Landline Telephone)
 Electronic communication system is to transfer
information from one place to another
Receiver
Transmitter Channel
Connection
- Wireless (ex. Radio Transmission)

3. Communication System
Message Signal
Output
Transducer
Output Signal
Input
Transducer
Transmitter
Communication
Channel
Input Message
Transmitted Signal
Receiver
Output Message
Received Signal
Noise

4.  Input Transducer
- Converts the messages produces by a source (speech,
temperature , image, music, …) into a form suitable for
electrical communications
- Speech waves are converted by
microphone to voltage variations
A transducer is a device that converts one form of energy to another form of energy.

5. On December 12, 1901, Marconi signaled the letter ‘S’ over the
Atlantic — from Cornwall, England to Newfoundland, Canada —
becoming the first to make a wireless radio transmission.

6.  Voice pattern or any other pattern of information
are low frequency, (Human Voice frequency
range 300 – 3400 Hz)
 All forms of information must be converted
to electromagnetic energy before being
propagated through an electronic
communication system.
FrequencySignalEnergy 
 Modulation is the process of increasing the
frequency content of a signal (and so energy
of the signal to enable it to travel long
distance).

7. Frequency-domain description
(Spectrum domain )

9. The electromagnetic frequency spectrum

11. Classification of the Modulation Process
 Modulation process uses a low frequency or
base-band signal (voice, image, …) to modify a
high frequency carrier signal

12.  Modulation process uses a low frequency or
base-band signal (voice, image, …) to modify a
high frequency carrier signal

13. Ex m(t)M(f) c(t) C(f)
C(t) = cos(2π1500𝑘)
S(t) = m(t) cos(2π1500𝑘)
M(t)AM-Radio channel
M
15KHz
1500KHz
fc
C(t) C(f)m(t)M(f)
 Modulation is the process of increasing the
frequency content of a signal (and so energy
of the signal to enable it to travel long
distance).

15. Ch1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7 Ch8
526.5KHz 1606.5KHz
EM wave to
electrical signal
BPF
1-Select the desired signal
2-Amplifed the received signal
Extract the message
(information audio signal )
2-Amplifed the audio signal
Electrical signal to
sound signal
Tuned Radio Frequency (TRF) Receivers

16. Problem
How can we use TRF receivers to tuned over the Broadcasting ( AM radio range) ?
Ch1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7 Ch8
526.5KHz 1606.5KHz

17. make the receiver stages speak one language
(the same frequency )(IF)
Superheterodyne Receiver

19. Superheterodyne Receiver
Superheterodyne receiver solve the
problem of selectivity in TRF receivers
m(𝐭)cos(𝟐𝝅𝒇 𝒄 𝒕)
cos(𝟐𝝅𝒇 𝑳𝒐 𝒕)
m(𝐭)cos(𝟐𝝅𝒇 𝑰𝒇 𝒕)