Data Transmission (Analog vs Digital, Modes) : MCQs & PYQs with Explanation

Option B

A Half-Duplex connection allows communication in both directions, but only one direction at a time. When one device is transmitting data, the other device must wait until the transmission is finished before sending data.
For example, in a walkie-talkie, both persons can communicate with each other, but they cannot normally speak at the same time. One person speaks while the other listens, and then they switch roles.

Option D

Industrial, Scientific, and Medical (ISM) bands are portions of the radio spectrum reserved internationally for non-commercial purposes like industrial heating, medical equipment, and scientific experimentation. Over time, they have also been widely used for unlicensed wireless communication, such as Wi-Fi and Bluetooth.

Option C

Manchester Encoding is a digital line‑coding scheme used at the physical layer to transmit data along with clock information. Each bit period is split into two phases, and there is always a transition in the middle of the bit, which provides self‑clocking and helps the receiver stay synchronized.
So, Manchester Encoding is used in the Physical Layer and provides signal synchronization through frequent transitions. It is called a Biphase Code because each bit has two phases, and its required transition occurs at the center of the bit, not necessarily at the bit boundary.

Option A

A scrambler is used in line coding schemes to modify the original data before transmission.

• To remove long sequences of 0s or 1s which can cause synchronization problems.
• To make the transmitted data appear random, even if the original data has patterns.
• Helps in maintaining clock synchronization between sender and receiver.

Option B

A coaxial cable consists of multiple layers designed to transmit signals efficiently with minimal interference. Its construction includes:

• A solid inner conductor (usually copper) to carry the signal.
• An insulating layer (dielectric) surrounding the conductor.
• An outer conductive sheath (shield) to protect against noise and interference.
• Often an outer protective jacket.

Option D

Digital Data Transmission is considered more secure because the data can be encrypted before transmission. Encryption converts the original information into a coded form so that unauthorized users cannot easily understand or access the data.
In digital communication systems, techniques such as encryption, encoding, and authentication are commonly used to improve security during data transfer.

Option C

Encoding schemes in Ethernet convert data bits into transmittable symbols over physical media (fiber/copper). They ensure clock recovery (frequent transitions), DC balance (equal 0s/1s), and error detection by adding overhead bits.
In Gigabit Ethernet (1000BASE-X), data transmission uses an encoding scheme to ensure reliable communication, proper synchronization, and error detection. The scheme used is 8B/10B encoding.
In this technique, 8 bits of actual data are converted into 10-bit code groups before transmission. This extra 2 bits help in:

• Maintaining signal balance (DC balance).
• Providing clock synchronization.
• Detecting transmission errors.

Therefore, 1000BASE-X uses 8B/10B encoding, where 8-bit data is converted into 10-bit groups for reliable high-speed transmission.

Option D

In satellite communication, signals travel between the earth station and the satellite using different frequencies. There are two main communication links:

• Uplink : Transmission from earth station to satellite.
• Downlink : Transmission from satellite to earth station.

The frequency used for sending signals from the satellite to the earth station receiver is called the Downlink Frequency.
For example, a TV broadcast satellite sends signals to home dish antennas using downlink frequency.

Option B

In digital communication, Modulation is the process of varying a carrier signal (sine wave) to transmit data. Digital modulation schemes often use two or more carriers, which can vary in amplitude, phase, or frequency to represent binary information.

A Constellation Diagram is a graphical representation of these modulated signals on a 2D plane, where the x-axis represents the in-phase component (I) and the y-axis represents the quadrature component (Q). Each point in the diagram corresponds to a unique amplitude and phase combination, allowing engineers to visualize the transmitted symbols and detect errors.

Option A

In data communication, Simplex Mode is a type of transmission where data flows in only one direction with no possibility of data flowing back, like traffic on a one-way street. One device acts as the sender, and the other only receives.
In Computer to Printer communication, data flows only from the computer to the printer. The printer does not send data back to the computer. This is a perfect example of simplex communication.

Option B

A Walkie-Talkie uses the Half-Duplex communication method. In half-duplex communication, data can travel in both directions, but not at the same time.
In a walkie-talkie:

• One person speaks while the other listens.
• Both persons cannot speak simultaneously.
• Users press a button to talk and release it to receive messages.

Option C

In digital communication, the quality or error performance of transmission is measured using BER (Bit Error Rate).
BER represents the number of bits received incorrectly compared to the total number of bits transmitted.

• It tells how reliable the communication system is.
• BER = Number of Error Bits / Total Number of Transmitted Bits

For example, if 1000 bits are transmitted and 10 bits are received incorrectly, then:
BER = 10/1000 = 0.01
A lower BER means better transmission quality.

Option A

In figure (a), the binary signal consists of 0s and 1s. In figure (b), the carrier signal is present when the binary input is 1, while the carrier is absent when the binary input is 0.
Thus, the information is represented by changing the amplitude of the carrier according to the binary signal.
For the given sequence, 0 1 0 1 1 0 0 1 0 0 1 0 0, the output waveform in figure (b) behaves as follows:

• Binary 0 : No carrier / Zero amplitude.
• Binary 1 : Carrier is present with amplitude.

This is a form of Amplitude Shift Keying (ASK), specifically On-Off Keying (OOK) when the carrier is completely switched off for binary 0.

Option B

The number of bits in the cable means the number of bits that can be present in the cable at one time.
The number of bits present in a cable at a particular time can be calculated using the Bandwidth-Delay Product. The formula is, Number of bits = Data Rate * Propagation Delay.
The length of the cable is 100 km and the signal speed is 2/3 of the speed of light. Since the speed of light is 3 * 10⁸ m/s, the signal speed in the cable is (2/3)*3*10⁸ = 2*10⁸ m/s.
First, convert the cable length into meters: 100 km = 100*10³ = 10⁵ m. Therefore, the propagation delay is 10⁵/(2*10⁸) = 0.0005 seconds. 
The data rate is 1.536 Mbps = 1.536*10⁶ bits per second. Hence, the number of bits in the cable is 1.536*10⁶*0.0005 = 768 bits.
Therefore, the cable can contain 768 bits at a time.

Option B