AM-Radio

- Direct (ex. Landline Telephone)

Electronic communication system is to transfer information from one place to another

ReceiverTransmitter Channel

Connection - Wireless (ex. Radio Transmission)

Communication System

Message Signal

OutputTransducer

Output Signal

Input Transducer

Transmitter

CommunicationChannel

Input Message

Transmitted Signal

Receiver

Output Message

Received Signal

Noise

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.

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.

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).

Frequency-domain description

(Spectrum domain )

The electromagnetic frequency spectrum

Classification of the Modulation Process

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

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

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

15KHz1500KHz

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).

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

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

make the receiver stages speak one language

(the same frequency )(IF)

Superheterodyne Receiver

Superheterodyne Receiver

Superheterodyne receiver solve the

problem of selectivity in TRF receivers

m(𝐭)cos(𝟐𝝅𝒇𝒄𝒕)

cos(𝟐𝝅𝒇𝑳𝒐𝒕)

m(𝐭)cos(𝟐𝝅𝒇𝑰𝒇𝒕)