1. Communication Systems.
-Girija Nair

2. Transmission of information from a source at one place to receiver at another place is called COMMUNICATION.
Three main parts:
a) Transmitter
b) Communication channel
c) Receiver.
Microphone and loudspeaker – transducer – convert energy from one form to another.

3. Drawbacks: Modifications:
Audio-frequency (20Hz-20kHz) – small power – cannot be radiated to very long distances.
Different transmitter signal – different frequencies – simultaneously – Interference.
Modifications:
Audio frequency message signal – superimposed on radio frequency waves – Modulation.
Single receiver tuned to pick up desired frequency.

4. Basic Technology in communication:
Transducer
Signal
Noise
Transmitter
Receiver
Communication Channel:
Guided Communication Channel.
Unguided Communication Channel.
Attenuation
Amplification
Modulation
Demodulation
Antenna

5. Bandwidth of Signals: Signal Frequency Range Bandwidth
Frequency range of a signal –Frequency band.
Difference in highest and lowest frequency – Bandwidth.
Signal
Frequency Range
Bandwidth
Speech
300Hz-3100Hz
2800Hz
Music
20Hz-20kHz
19980Hz TV
1500MHz-1506MHz
6MHz
Computer Data
2000MHz-2600MHz
600MHz

6. Bandwidth of Transmission Medium: Wire Free-space. Nature of Broadcast
Transmission channels- two types:
Wire
Free-space.
Nature of Broadcast
Frequency Band
AM Broadcast
KHz
FM Broadcast
88-108MHz
VHF (TV)
54-72MHz, MHz
UHF (TV)
MHz
Cellular Mobile
MHZ (mobile to base station), MHz (base station to mobile)
Satellite Communication
GHz (Uplink)
GHz (Downlink)

7. Modes of Propagation – Electromagnetic (Radio) Waves – Atmosphere.
Ground- wave Propagation
Sky- wave Propagation
Space-wave propagation.

8. Next Class Topic – Types of Modulation.