Need of Modulation

Need of modulation is essential in communication systems for several reasons:

1. Efficient use of the frequency spectrum: Modulation allows multiple signals to be transmitted simultaneously over the same channel without interference. By modulating signals at different frequencies, they can coexist without overlapping and causing interference with each other. This enables efficient use of the limited frequency spectrum available for communication.

2. Long-distance transmission: Modulation helps in transmitting signals over long distances. High-frequency carrier waves can carry information across vast distances more effectively than lower-frequency signals. Modulating a high-frequency carrier with the information signal enables the transmission of this information over long distances without significant loss.

3. Noise and interference reduction: Modulation techniques can make transmitted signals less susceptible to noise and interference. For instance, frequency and phase modulation techniques often provide better resilience against noise compared to amplitude-based techniques like AM. By modulating the carrier signal, the original information can be retrieved more accurately at the receiving end, even in the presence of disturbances.

4. Compatibility and versatility: Different types of modulation techniques are used based on specific requirements. For example, AM is commonly used in broadcasting, FM is prevalent in high-quality audio transmission, and digital modulation schemes like PSK and QAM are extensively used in digital communication systems. This versatility allows for compatibility among various systems and enables the transmission of different types of information.

5. Security and encryption: Certain modulation techniques are used in secure communication systems to encrypt and encode information. Techniques like spread spectrum modulation are employed for secure transmission, making it difficult for unauthorized entities to intercept or decipher the transmitted data.

In summary, modulation is crucial for efficient, reliable, and versatile communication. It enables the transmission of information over long distances, reduces interference, optimizes spectrum use, and facilitates various types of communication systems catering to different needs, ultimately enhancing the overall effectiveness of communication networks.

Size of Antenna

Signals are transmitted via EM waves. EM waves are transmitted by using an antenna. What will be the size of antenna?

Antena height must be multiple of λ/4 .

Where λ = c/f. λ is inversely proportional to frequency.

λ = c/f = 300000000/3000 = 100000 =100Km

Antena height = λ/4 = 100000/4 = 25000= 25Km

Radiated Power

P = 1/ λ²

λ = c/f

P = 1/ (c/f)²
P = f ² / c ²

• To minimize the interference from other signals.(commercial FM stations transmits voice without any interference).

• High frequency carrier travel a greater distance.Low frequency signal carries low energy.

• Multiplexing is possible.Multiple signals can use same medium.