HISTORY :

Year Invention/Event Inventor/Note

1835 Telegraph Morse & Wheatstone
1876 Telephone Alexander Graham Bell
1887 Radio Waves Heinrich Hertz
1896 Wireless Transmission Marconi
1910 First Radio Broadcast Lee De Forest
1926 Electronic TV concepts John Logie Baird
1936 TV Broadcasting UK
1946 Mobile Radio Telephone AT&T
1957 Sputnik Satellite USSR
1962 Telstar Satellite USA
1969 Cellular System Bell Labs
1970s Computer Comm. Internet emerges
1980s Personal Devices Pager, Mobile
2000s GPS & Broadband Everywhere
Now Fiber + Wireless High-speed mobile comm

⚡ Electromagnetic Spectrum – Easy Explanation

📡 What is it?

The electromagnetic spectrum refers to the range of all types of electromagnetic waves (EM waves) that carry
energy through space or medium.

These waves include☹(RIMX)

 Radio waves
 Microwaves
 Infrared
 Visible light
 Ultraviolet
 X-rays
 Gamma rays

📶 Where do signals travel?

Medium Type How EM Waves Travel Example
Wireline Voltage or current along a metal wire Telephone wire, LAN cables
Wireless (Free space) EM waves (radio, microwave) travel in air Mobile phones, Wi-Fi
Optical fiber Light waves (very high-frequency EM waves) Internet fiber cables

Wavelength (λ) and Frequency (f) Relationship

🧠 Formula:
λ=c/f
Where:
 λ (lambda) = Wavelength in meters
 c = Speed of light in free space = 3 × 10⁸ m/s
 f = Frequency in Hz (Hertz)

📡 What is an EM Wave? A combination of electric and magnetic fields

 Travels through air, wire, or vacuum

 Called an electromagnetic wave (EM wave)

📻 Key Points About Radio Signal

Transmission

 Uses one frequency or narrow band

 Distributed across a wide range of
frequencies
 Useful EM spectrum ranges from 10 kHz to billions of Hz
 RF spectrum is divided into specific bands

📶 Electromagnetic Frequency Spectrum – Extra Lines (Short & Easy)

 The electromagnetic spectrum is the entire range of frequencies over which electromagnetic waves can travel.
 These waves do not need any medium — they can travel through vacuum or space.
 The spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma
rays.
 In communication systems, we mostly use the radio frequency (RF) portion of the spectrum.
 Each band in the RF spectrum is used for a specific application, like:
 Higher frequency means more data-carrying capacity but less coverage area.
Electronic Communication System

🔹 1. Input Transducer

 The input transducer takes the original message (sound, light, etc.) and converts it into an electrical signal.
 A transducer is a device that converts one form of energy into another.
 This electrical signal is suitable for further processing by the transmitter.
 📌 Example: A microphone converts your voice into electrical signals.

🔹 2. Transmitter

 The transmitter processes the electrical signal received from the input transducer.
 It may amplify (boost) the signal and modulate it.
(Modulation means combining the signal with a high-frequency carrier to make it suitable for long-distance
transmission.)
 It then sends the signal into the communication channel.
 📌 Example: A mobile phone transmitter modulates and sends your voice as a radio signal.
🔹 3. Communication Channel

🔸 The pathway through which the signal travels from transmitter to receiver.

 This is the medium or path through which the signal travels.

 Can be wired (like coaxial cable, optical fiber) or wireless (like air or vacuum using radio waves).
 Noise may be added here — it is any unwanted signal that interferes with the original message.
 📌 Example: Air (in wireless systems) or fiber cable (in broadband).

 Air is the channel when you're using a mobile call; fiber optic cable is used in broadband internet.

🔹 4. Receiver

 The receiver receives the signal from the communication channel.

 It filters out the noise, demodulates the signal (if modulated), and amplifies it if needed.
 Its job is to recover the original message signal as accurately as possible.
 📌 Example: Your friend’s mobile receiver that processes your call.2

🔹 5. Output Transducer

 The final block of the system.

 It converts the received electrical signal back to its original form (like sound or image).
 📌 Example: A speaker that plays back your voice.

📡 Primary Communication Resources – Easy Explanation

In any electronic communication system, there are two main resources that we need to manage carefully:

1️⃣ Transmitted Power

 This is the strength of the signal sent by the transmitter.

 More power = stronger signal at the receiver.
 It directly affects the Signal-to-Noise Ratio (SNR) — the ratio between the actual message signal and the
unwanted noise.
 📌 Higher SNR = better clarity and longer range.
 If the power is too low, the receiver may not hear the signal clearly due to noise.

2️⃣ Channel Bandwidth

 This is the range of frequencies a channel can carry.

 📌 Think of it like the width of a road — wider bandwidth allows more data (or faster transmission).
 Every signal has multiple frequency components (in the form of its spectrum).
 The channel must pass all these frequencies correctly — keeping their amplitude and phase intact — to avoid
distortion.

Resource Description
Power Controls SNR and range (more power = clearer signal)
Bandwidth Determines how much data can be transmitted (wider = better)
SNR Must be high enough for clear communication
📑 Types of Information Sources – Easy Explanation
In communication systems, the information we want to send can come in two types:

1️⃣ Analog Information Source

 Produces signals that change smoothly and continuously over time.

 The signal has infinite possible values within a range (not fixed steps).
 📌 Examples:
o Microphone: Converts voice into a smooth, changing electrical signal.
o Video camera: Scans a picture and outputs a continuous signal.

✅ Use when the input is natural or real-world like sound or images.

2️⃣ Discrete Information Source

 Produces signals in separate, fixed steps or symbols (not continuous).

 The output is digital — like 0s and 1s (binary).
 📌 Examples:
o Computer output: Digital binary data.
o Teletype: Sends text characters one at a time as coded symbols.

✅ Use for digital communication like data from a computer or keyboard.

📡 Types of Communication Channels – Easy Explanation

A communication channel is the path that carries the signal from the transmitter to the receiver. There are mainly
two types:
1️⃣ Wireline (Wired) Communication Channel
 Signal travels through a physical medium like a wire or cable.
 📌 Examples:
o Twisted pair cable – used in telephone lines
o Coaxial cable – used for cable TV
o Optical fiber – used for high-speed internet
✅ Advantages:
 Less affected by interference
 Stable and secure connection

2️⃣ Wireless Communication Channel

 Signal travels through free space (air) as electromagnetic waves.

 📌 Examples:
o Radio waves – used in FM, AM
o Microwaves – used in mobile phones, satellite
o Infrared, Bluetooth, Wi-Fi – used in short-range communication

✅ Advantages:

 No need for cables

 Useful for mobile and long-distance communication

🔁 Modes of Communication – Easy Explanation

Communication between two devices can happen in three different ways:

1️⃣ Simplex Mode

 Information flows in only one direction.

 One device only sends, the other only receives.
 📌 Example:
o TV broadcast – The station sends; your TV only receives.
o Keyboard to computer – Keyboard sends input; computer receives it.

✅ No two-way communication

2️⃣ Half-Duplex Mode

 Information can flow in both directions, but only one way at a time.
 Like a walkie-talkie: one person speaks, the other waits, then replies.
 Push-To-Talk (PTT) button is used to switch between sending and receiving.

📌 Example:

 Walkie-talkies used by police and security forces.

✅ Two-way communication, but one at a time

3️⃣ Full-Duplex Mode

 Information flows in both directions at the same time.

 Both users can talk and listen simultaneously.
 Used in modern communication systems for smooth interaction.

📌 Examples:

 Mobile phone calls

 Landline telephones
 Internet (LAN, data communication)

✅ Fast, real-time two-way communication

✅ Summary Table:

Mode Direction Example

Simplex One-way only TV broadcast, keyboard
Half-Duplex Two-way, one-at-a-time Walkie-talkies, police radios
Full-Duplex Two-way, same time Phone calls, Internet, satellite

📶 Signal Transmission Concept – Easy Explanation

🔹 1️⃣ Information/Data Signal
  This is the original message we want to send — like voice, text, video, or data.
 It can be:
o Analog: continuously changing (like speech, music)
o Digital: in bits (0s and 1s)

📌 Example: Your voice when you speak into a phone is an analog information signal.

🔹 2️⃣ Baseband Signal

 A baseband signal is the original form of the signal (before modulation).

 It has low frequency and contains the actual information.
 Baseband signals are usually not suitable for long-distance wireless transmission.

📌 Example:

 Microphone output
 Audio signal from a music player
 Digital signal from a computer

🔹 3️⃣ Passband Signal

 A passband signal is created by modulating the baseband signal onto a high-frequency carrier wave.
 This helps in long-distance transmission (especially wireless).
 It occupies a specific range of frequencies (band) around the carrier.

📌 Example:

 FM radio, TV signals, mobile phone signals — all are passband signals

📡 Modulation – Easy Explanation

🔷 What is Modulation?

Modulation is the process of changing a carrier signal (usually high frequency) by mixing it with the information
signal (voice, data, etc.).

We change one of the carrier’s properties — amplitude, frequency, or phase — based on the data.

📌 Example:
When you speak during a mobile call, your voice (low frequency) is modulated onto a radio wave (high frequency) and
sent wirelessly.

❓ Why is Modulation Needed?

1️⃣ Baseband signals can't travel wirelessly directly

 Their frequency is too low

 Antennas required would be too large
2️⃣ Simplifies transmitter and receiver design

 High-frequency signals are easier to handle.

3️⃣ Allows Frequency Division Multiplexing (FDM)

 Multiple signals can be sent on different frequencies using one channel

4️⃣ Reduces noise and distortion

 Modulated signals are more stable during transmission

🔀 Types of Modulation
1️⃣ Analog Modulation

 Both the information signal and carrier are analog.

 📌 Types:
o AM (Amplitude Modulation) – change amplitude
o FM (Frequency Modulation) – change frequency
o PM (Phase Modulation) – change phase

📌 Example:
FM Radio uses Frequency Modulation (FM) to send sound.

2️⃣ Pulse Modulation

 The message is analog, but the carrier is a series of pulses.

 📌 Types:
o PAM – Pulse Amplitude Modulation
o PWM – Pulse Width Modulation
o PPM – Pulse Position Modulation
o PCM – Pulse Code Modulation (digital version)

📌 Example:
Audio signals in telephones can be converted into PCM signals.

3️⃣ Digital Modulation

 The message is digital (like binary 0s and 1s), and the carrier is analog.
 📌 Types:
o ASK – Amplitude Shift Keying
o FSK – Frequency Shift Keying
o PSK – Phase Shift Keying

📌 Example:
Wi-Fi and digital communication use FSK or PSK techniques.

🔄 Frequency Translation – Super Easy Explanation

✅ What is it?
 Changing the frequency of a signal to a higher value so it can travel better over long distances.

⚙️How is it done?
1️⃣ Mixing (Combining Signals)
 Two signals are mixed to get new frequencies.
 🔸 Linear Mixing: Uses simple circuits (like amplifiers).
 🔸 Non-linear Mixing: Uses components like diodes, JFETs — creates new frequencies (sum/difference)
2️⃣ FDM – Frequency Division Multiplexing
  Many signals sent at once, each on a different frequency using the same channel.
📌 Example: FM radio stations (all use different frequencies).

✅ One-line Summary:
Frequency translation helps send low-frequency signals at higher frequencies for better and multiple
transmissions.

📡 Signal Radiation and Propagation – Easy Explanation

🔷 What is Signal Radiation?

 Radiation means sending out the signal from the antenna into space as electromagnetic waves (like radio
waves, microwaves, etc.).
 When a transmitter sends a signal, it flows through the antenna and is radiated in all directions into the air or
space.

📌 Example:
When you call someone on your mobile, your phone’s antenna radiates the signal as radio waves.

🔷 What is Signal Propagation?

 Propagation means how the signal travels after it is radiated.

 It depends on many things like distance, obstacles, frequency, and weather.
 Signals can travel in different ways based on frequency:
o Ground wave (along Earth's surface)
o Sky wave (bounces off the ionosphere)
o Line-of-sight (direct path between antennas)

📌 Example:

 AM radio uses ground and sky waves to reach far places.

 TV and mobile signals use line-of-sight, so tall towers are needed.

✅ Summary in One Line:

Signal radiation sends the signal into space, and propagation is how it travels to reach the receiver.

MODULE 2
Types of Analog Modulation

Type of Modulation What Changes? Explanation Example

AM (Amplitude) Amplitude Vc Height of the carrier wave changes as per voice/music signal AM Radio
FM (Frequency) Frequency fc Number of wave cycles changes per second as per the signal FM Radio
PM (Phase) Phase angle φ The shift in the wave's starting point changes with signal Advanced wireless systems
📊 AM vs FM vs PM – Simple Comparison

Feature AM FM PM
What changes Amplitude Frequency Phase
Type Linear modulation Non-linear (Angle modulation) Non-linear (Angle modulation)
Noise resistance Low High High
Bandwidth requirement Low Higher than AM Similar to FM

📌 Final Summary:

 AM: Change in height of the wave

 FM: Change in speed of wave cycles
 PM: Change in starting point of the wave
 Used to send analog signals over long distances using radio waves

📻 Principle of Amplitude Modulation (AM) – Easy Explanation (am envelope)

🔷 What is AM?
Amplitude Modulation means changing the amplitude (height) of a high-frequency carrier wave in proportion to
the information signal (like voice or music).
✅ Only the amplitude changes, frequency and phase stay the same.
🔸 Basic Signals Used:
1️⃣ Modulating Signal (Message):
A low-frequency signal (like audio or voice)
🧾 Formula:
vm(t) = Vm × sin(2πfmt)
 Vm = max amplitude of voice/music
 fm = frequency of voice/music (low)

2️⃣ Carrier Signal:

A high-frequency sine wave that carries the message
🧾 Formula:
vc(t) = Vc × sin(2πfct)
 Vc = max amplitude of carrier
 fc = carrier frequency (high, like 1000 kHz)

🔁 AM Signal (Modulated Output)

🧾 Formula:
vAM(t) = [Vc + vm(t)] × sin(2πfct)
This means:
 The amplitude of the carrier is varied based on the message signal.
 The shape of the carrier now follows the message waveform.

🎯 Key Points:

✅ When no message signal, AM wave = normal carrier wave

✅ When message is present, AM wave’s amplitude follows the message
✅ Carrier frequency stays same

📏 Modulation Index (m)

Ma=Vm
Vc
Where:

 Vm = amplitude of modulating signal (message)

  Vc = amplitude of carrier signal

📻 Limitations of AM – Explained with Example

🔸 Imagine:

You're listening to AM radio in your car while driving on a highway.

🎯 Limitation 1: Low Efficiency

🔹 In AM, most of the power goes into transmitting the carrier wave, which carries no actual message.
🔹 Only the sidebands carry the voice or music, and they use very little power.

📌 Example:
Out of 100 watts transmitted, maybe 80 watts go to the carrier, and only 20 watts go to your actual audio. That’s a
waste of power.

🎯 Limitation 2: Noise and Distortion

🔹 AM is easily affected by noise like engine ignition, lightning, or electrical devices.

🔹 This happens because noise also affects amplitude, and AM relies on amplitude to carry information.

📌 Example:
You hear static or buzzing sounds suddenly while listening to music — that’s AM noise.

🎯 Limitation 3: Overmodulation

🔹 If the audio signal is too strong, it can over-modulate the carrier.

🔹 This causes signal distortion, and the receiver won’t be able to recover the voice correctly.

📌 Example:
A loud shout on a live AM broadcast may cause the sound to crackle or break due to overmodulation.

🎯 Limitation 4: Bandwidth Waste

🔹 AM uses double the bandwidth — one for upper sideband and one for lower.
🔹 This limits how many stations can be broadcast in a region.

📌 Example:
If your voice has a frequency range of up to 5 kHz, AM needs 10 kHz — which is not efficient.

🎯 Principle of Angle Modulation – Easy Explanation

🔷 What is Angle Modulation?

Angle Modulation is a technique where the angle (or phase) of a carrier wave is varied according to the message
signal (modulating signal), while the amplitude remains constant.

In short:
We change the frequency or phase of the carrier depending on the information signal.
🔄 Types of Angle Modulation:

1. Frequency Modulation (FM)

o Frequency of the carrier is varied by the message signal
o Phase remains constant
2. Phase Modulation (PM)
o Phase of the carrier is varied by the message signal
o Frequency changes as a result of phase change

📊 FM vs PM Summary Table:
Aspect Frequency Modulation (FM) Phase Modulation (PM)

Varies with Integral of message signal Direct value of message signal

Equation …………. ………………………..

Main change
Frequency Phase
in

Type of
Angle modulation Angle modulation
modulation
This diagram explains FDM (Frequency Division Multiplexing) for 3 voice channels in a simple way.

🧠 What is FDM?

FDM means sending multiple signals at the same time using different frequency ranges (bands). It’s like giving each
signal its own lane on a highway to avoid collisions.

🔍 Step-by-Step Explanation of the Diagram (Fig. 1.22)

1. Voice Channels (Input):

We have 3 different voice channels.

Each voice channel carries a signal with frequency range:
300 Hz to 3400 Hz (normal range of human speech).

2. ⚙️Mixers:

Each voice signal is passed through a mixer.

Voice Channel Mixer Frequency

Voice 1 12 kHz
Voice 2 16 kHz
Voice 3 20 kHz

✅ Mixing means shifting the frequency of the voice signal to a higher band.
This is done to avoid overlap between signals.

3. Low-Pass Filters (LPF):

Each mixed signal is passed through a low-pass filter to:

 Limit the bandwidth

 Keep only the needed frequency range

Voice Output Band After Filter

1 8.6 – 11.7 kHz
2 12.6 – 15.7 kHz
3 16.6 – 19.7 kHz

4. 🔗 Multiplexing:

Now, all 3 filtered signals are combined together (multiplexed).

They do not interfere because they lie in different frequency bands.

🎯 This combined signal is called FDM Output.

📐 Guard Bands:

There are small gaps (0.9 kHz) between channels.

These are called guard bands and they prevent interference (overlap) between signals.

✅ Summary:

 3 voice signals (each 300–3400 Hz) are shifted to different frequency ranges
 Then combined into one composite signal
 This is FDM — carrying multiple signals over a single communication channel without overlap

✅ Advantages of Digital Transmission:

🎯 Mnemonic: “DANGER-C”

Each letter stands for one key advantage:

Letter Stands For Explanation

D Durability (Less noise) Digital signals resist noise and distortion

A Accuracy (Error correction) Error detection/correction is possible

N Noise immunity Less affected by electromagnetic noise

G Good for storage Digital data is easy to store/compress

E Encryption possible Digital signals can be secured easily

R Regeneration of signal Repeaters restore signal without noise

C Compatibility with computers Works well with modern digital systems