β MES Jr. Grade
Past Questions
Transmitted pulse becomes distorted due to:
A)
Ideal transmission characteristic
B)
Non ideal transmission characteristic
C)
All of the mentioned
D)
None of the mentioned
In pulse communication, a transmitted pulse consists of a wide range of frequency components (Fourier spectrum). For a pulse to be transmitted without distortion, the transmission medium (channel) must have an 'ideal' characteristic, meaning it must provide a constant amplitude response (flat gain) and a linear phase response (constant group delay) across all the frequency components of the pulse.
1. **Ideal Transmission Characteristic**: If the channel is ideal, all frequency components of the pulse are attenuated equally and delayed by the same amount of time, resulting in a received pulse that is an exact replica of the transmitted pulse (only scaled in amplitude and shifted in time).
2. **Non-ideal Transmission Characteristic**: In real-world scenarios, channels exhibit frequency-dependent attenuation (amplitude distortion) and non-linear phase shifts (phase distortion/dispersion). When different frequency components of a pulse travel at different speeds or are attenuated differently, the pulse shape changes, leading to 'distortion' (e.g., pulse broadening or ringing).
Therefore, distortion is caused specifically by the non-ideal nature of the transmission characteristics.
Which of the following instruction is an example of direct addressing mode of 8086?
A)
MOV CH, BL
B)
MOV BH, 23h
C)
MOV DX, [1234h]
D)
MOV AX, [BX+08h]
In the 8086 microprocessor, addressing modes define how the CPU accesses data.
1. **Direct Addressing Mode**: In this mode, the effective address (offset) of the operand is specified directly within the instruction. It is typically denoted by square brackets containing a constant value. In option (c), `MOV DX, [1234h]`, the operand is located at the memory offset 1234h. The CPU calculates the physical address as (DS * 10h) + 1234h. This is a classic example of direct addressing.
2. **Analysis of other options**:
- **Option (a) MOV CH, BL**: This is **Register Addressing Mode**. Both the source and destination are registers.
- **Option (b) MOV BH, 23h**: This is **Immediate Addressing Mode**. The actual data (23h) is provided immediately within the instruction.
- **Option (d) MOV AX, [BX+08h]**: This is **Based Addressing Mode** (or Indexed/Relative). The address is calculated by adding a displacement (08h) to the contents of a base register (BX).
What is the purpose of modulation in communication systems?
A)
To eliminate noise from the signal
B)
To increase the frequency of the signal
C)
To encode information onto a carrier wave for transmission
D)
To amplify the transmitted signal
Modulation is the process of varying one or more properties (amplitude, frequency, or phase) of a high-frequency periodic waveform (called the carrier wave) with a modulating signal (the information or baseband signal).
Step-by-step reasoning:
1. Baseband signals (like voice or music) have low frequencies and cannot be transmitted efficiently over long distances because they would require impractically large antennas (antenna size is typically proportional to wavelength, Ξ» = c/f).
2. By modulating the information onto a high-frequency carrier wave, the signal can be transmitted over the air with reasonable antenna sizes and can be multiplexed (multiple signals sent over the same medium at different frequencies).
Analysis of options:
- Option (a) is incorrect: Modulation does not eliminate noise; in fact, some modulation schemes are more susceptible to noise than others, although some (like FM) provide better noise immunity than others (like AM).
- Option (b) is partially true in a physical sense (the resulting signal has a higher frequency), but 'increasing the frequency' is the mechanism, not the 'purpose'. The purpose is the transmission of information.
- Option (c) is correct: This is the fundamental definition and purpose of modulation.
- Option (d) is incorrect: Amplification is handled by amplifiers (power amps), not by the process of modulation itself.
A special request originated from some device to the CPU to acquire some of its time is called:
A)
Disturbance
B)
Attenuation
C)
Interrupt
D)
Noise
In microprocessor architecture, an 'Interrupt' is a signal sent by a hardware device or a software program to the CPU, requesting that the CPU temporarily suspend its current execution flow to handle a specific event or task. Once the Interrupt Service Routine (ISR) is completed, the CPU returns to the original task it was performing.
Analysis of other options:
- a. Disturbance: This is a general term and not a technical term used in microprocessor architecture to describe CPU requests.
- b. Attenuation: This refers to the gradual loss in intensity of any kind of flux (like signal strength in a cable) as it passes through a medium; it is a telecommunications/electronics term, not a CPU request mechanism.
- d. Noise: This refers to unwanted electrical signals that interfere with the transmission of data; it is a problem to be filtered out, not a request for CPU time.
Describe the difference between TE and TM modes in a waveguide, with an example of each.
Describe how a Gunn diode generates microwave oscillations.
Standing waves are formed in a transmission line when:
A)
Impedance is matched
B)
There is a reflection due to impedance mismatch
C)
Power is transmitted efficiently
D)
The frequency of the source matches the load
In a transmission line, standing waves are the result of the interference between the incident wave (traveling from the source to the load) and the reflected wave (traveling from the load back to the source).
1. **Impedance Matching**: When the load impedance ($Z_L$) is exactly equal to the characteristic impedance ($Z_0$) of the line, all the energy is absorbed by the load. No reflection occurs, and therefore no standing waves are formed. This is known as a 'matched' line.
2. **Impedance Mismatch**: When $Z_L \neq Z_0$, a portion of the incident voltage and current is reflected back toward the source. The superposition of the incident and reflected waves creates a stationary pattern of voltage and current amplitudes along the line, known as a Standing Wave.
3. **Standing Wave Ratio (SWR)**: The degree of mismatch is measured by the Voltage Standing Wave Ratio (VSWR). A VSWR of 1 indicates a perfect match (no standing waves), while a VSWR > 1 indicates a mismatch and the presence of standing waves.
Analysis of other options:
- Option (a) is incorrect because matching prevents standing waves.
- Option (c) is incorrect because standing waves actually indicate inefficiency, as power is reflected back to the source rather than being delivered to the load.
- Option (d) is incorrect because the frequency of the source does not determine the formation of standing waves; the relationship between the line's characteristic impedance and the load impedance does.
To reduce the memory access time we generally make use of:
A)
SDRAM
B)
Heaps
C)
Cache
D)
Higher capacity RAM
The goal of reducing memory access time is to bridge the 'processor-memory gap'βthe difference between the high speed of the CPU and the relatively slow speed of main memory (RAM).
1. **Cache Memory (Correct):** Cache is a small, high-speed SRAM (Static RAM) located very close to or inside the CPU. It stores frequently accessed data and instructions. Because it operates at speeds close to the CPU clock, it significantly reduces the average memory access time by avoiding the need to access the slower main memory for every request (a concept known as 'locality of reference').
2. **SDRAM (Incorrect):** Synchronous Dynamic RAM is a type of main memory. While it is faster than older asynchronous DRAM, it is still significantly slower than cache memory and does not solve the fundamental latency issue between the CPU and RAM.
3. **Heaps (Incorrect):** A heap is a region of a computer's memory used for dynamic memory allocation in software programming. It is a logical memory management structure, not a hardware mechanism to reduce physical access time.
4. **Higher capacity RAM (Incorrect):** Increasing the capacity of RAM allows the system to hold more data and reduces the need to swap data to the hard disk (virtual memory), but it does not reduce the actual access time (latency) for a single piece of data retrieved from the RAM.
The radiation pattern of an antenna is a graphical representation of:
A)
Power distribution as a function of distance
B)
The impedance of the antenna
C)
Power distribution as a function of direction
D)
Frequency variation over time
The radiation pattern of an antenna is defined as a plot of the relative field strength (or power density) of the radiated electromagnetic waves as a function of the angular position (direction) relative to the antenna. It describes how the antenna distributes its energy in 3D space.
- Option (a) is incorrect because power distribution as a function of distance describes the 'attenuation' or 'path loss' of the wave, not the radiation pattern.
- Option (b) is incorrect because impedance is a property of the antenna's electrical characteristics (input impedance), not its spatial radiation characteristics.
- Option (d) is incorrect because frequency variation over time describes 'chirping' or modulation, which is unrelated to the spatial radiation pattern of an antenna.
The Nyquist theorem relates:
A)
Modulation index to channel capacity
B)
Sampling rate to maximum signal frequency
C)
Coding rate to SNR
D)
Bandwidth to optical wavelength
The Nyquist-Shannon Sampling Theorem is a fundamental principle in digital signal processing. It states that to perfectly reconstruct a continuous-time signal from its samples, the sampling frequency (fs) must be at least twice the highest frequency component (fmax) present in the signal. Mathematically, this is expressed as fs β₯ 2 * fmax. Therefore, the theorem directly relates the sampling rate to the maximum signal frequency.
Analysis of other options:
- Option (a) is incorrect because modulation index relates to the depth of modulation in AM/FM, and channel capacity is governed by the Shannon-Hartley theorem.
- Option (c) is incorrect because coding rate and Signal-to-Noise Ratio (SNR) are related to information theory and channel coding (e.g., Shannon's limit), not the Nyquist sampling theorem.
- Option (d) is incorrect because bandwidth and optical wavelength are physical properties of light and transmission media, unrelated to the sampling theorem.
If the sampling frequency is slightly more than twice the highest signal frequency, then:
A)
Perfect reconstruction is possible
B)
Aliasing will always occur
C)
Quantization error is reduced
D)
Bandwidth requirement doubles
According to the Nyquist-Shannon Sampling Theorem, a continuous-time signal can be perfectly reconstructed from its samples if the sampling frequency (fs) is greater than twice the highest frequency component (fmax) present in the signal. This critical threshold is known as the Nyquist Rate (fs = 2 * fmax).
1. Analysis of the condition: The question states that the sampling frequency is 'slightly more than twice the highest signal frequency' (fs > 2 * fmax).
2. Result: Since the Nyquist criterion is satisfied, the spectral replicas of the signal in the frequency domain do not overlap. This allows a low-pass filter (reconstruction filter) to isolate the original baseband signal perfectly without any distortion.
Why other options are incorrect:
- Option b: Aliasing occurs only when fs < 2 * fmax (undersampling). Since fs > 2 * fmax, aliasing is avoided.
- Option c: Quantization error is a result of the Analog-to-Digital conversion process (bit depth/resolution), not the sampling frequency.
- Option d: The bandwidth requirement for transmission depends on the sampling rate, but it does not 'double' simply because the rate is slightly above the Nyquist rate; it scales linearly with the sampling frequency.
How many flags are there in 8085 microprocessor?
A)
3
B)
5
C)
7
D)
9
The 8085 microprocessor has a Flag Register (also known as the Program Status Word) which is an 8-bit register. However, only 5 of these bits are used as status flags to indicate the results of arithmetic and logical operations. These five flags are:
1. Carry Flag (CY): Set if there is a carry out from the most significant bit (D7).
2. Parity Flag (P): Set if the result has an even number of 1s.
3. Auxiliary Carry Flag (AC): Set if there is a carry from bit D3 to D4 (used for BCD arithmetic).
4. Zero Flag (Z): Set if the result of an operation is zero.
5. Sign Flag (S): Set if the result is negative (most significant bit D7 is 1).
The other 3 bits in the 8-bit register are undefined/unused, which is why the correct answer is 5, not 8.
In an analog communication system, if the carrier frequency is 1 MHz, what is the upper sideband frequency for an AM signal with a modulation frequency of 5 kHz?
A)
995 kHz
B)
1.005 MHz
C)
1.0055 MHz
D)
5 kHz
In Amplitude Modulation (AM), the modulated signal consists of the carrier frequency and two sidebands.
1. **Given Data:**
- Carrier Frequency ($f_c$) = 1 MHz = 1000 kHz
- Modulating Frequency ($f_m$) = 5 kHz = 0.005 MHz
2. **Formula for Sidebands:**
- The Upper Sideband (USB) frequency is calculated as: $f_{USB} = f_c + f_m$
- The Lower Sideband (LSB) frequency is calculated as: $f_{LSB} = f_c - f_m$
3. **Calculation:**
- $f_{USB} = 1 ext{ MHz} + 0.005 ext{ MHz} = 1.005 ext{ MHz}$
- Alternatively, in kHz: $1000 ext{ kHz} + 5 ext{ kHz} = 1005 ext{ kHz} = 1.005 ext{ MHz}$
4. **Analysis of Options:**
- Option (a) 995 kHz is the Lower Sideband frequency ($1000 - 5$).
- Option (b) 1.005 MHz is the correct Upper Sideband frequency.
- Option (c) 1.0055 MHz is mathematically incorrect.
- Option (d) 5 kHz is simply the modulating frequency ($f_m$).
What is a directional coupler? Explain its function in microwave measurement setups.
Which type of transmission line is best suited for high-frequency applications?
A)
Coaxial cable
B)
Open wire line
C)
Twisted pair cable
D)
Waveguide
To determine the best transmission line for high-frequency applications, we must analyze the losses and characteristics of each option as frequency increases:
1. **Open wire lines and Twisted pair cables**: These are primarily used for low-frequency (power) or low-to-medium frequency (telecommunications) signals. At high frequencies, they suffer from massive radiation losses and high attenuation due to the skin effect and dielectric losses.
2. **Coaxial cables**: These are excellent for radio frequencies (RF) and microwave frequencies because the outer conductor shields the inner conductor, reducing radiation. However, as frequency reaches the microwave range (typically above 10-20 GHz), dielectric losses and skin effect losses become significant, leading to high attenuation.
3. **Waveguides**: These are hollow metallic pipes. Because they do not use a center conductor or a dielectric medium to support the wave (they guide the electromagnetic wave through the air or vacuum inside the pipe), they have extremely low attenuation and very low power loss at very high frequencies (Microwave and Millimeter-wave bands). They are specifically designed to operate above a certain 'cutoff frequency,' making them the gold standard for high-frequency/microwave applications.
Therefore, while coaxial cables are used for 'high' frequencies, waveguides are the 'best suited' for the highest frequency applications due to their superior efficiency and low loss.
In 8086 ALU is operated on _____________ data.
A)
8-bit
B)
16-bit
C)
20-bit
D)
32-bit
The Intel 8086 is a 16-bit microprocessor. This means its internal architecture, including the Arithmetic Logic Unit (ALU), general-purpose registers (like AX, BX, CX, DX), and the internal data bus, are all designed to process data in 16-bit chunks. While the 8086 can perform 8-bit operations (by accessing the lower half of the registers, e.g., AL or AH), the native width and the maximum capacity of the ALU to operate on data in a single cycle is 16 bits.
Analysis of other options:
- a. 8-bit: This is the characteristic of the 8085 microprocessor, not the 8086.
- c. 20-bit: While the 8086 has a 20-bit address bus to access 1MB of memory, the ALU does not perform arithmetic operations on 20-bit data.
- d. 32-bit: This is characteristic of later processors like the 80386.
What is eye pattern? What are the interpretations obtained from it?
In the von Neumann architecture, both program instructions and data are stored in:
A)
Separate memory units
B)
Same memory unit
C)
Cache memory only
D)
CPU registers only
The von Neumann architecture, proposed by John von Neumann in 1945, is based on the 'stored-program' concept. Its defining characteristic is that both the program instructions (the code) and the data being operated upon are stored in the same read-write electronic memory (RAM). This allows the CPU to fetch instructions and data using the same bus system.
Analysis of options:
- Option (a) 'Separate memory units' describes the Harvard Architecture, which uses separate memory paths for instructions and data to increase throughput.
- Option (c) 'Cache memory only' is incorrect because cache is a small, high-speed buffer used to speed up access to the main memory; it is not the primary storage for the entire program and data set.
- Option (d) 'CPU registers only' is incorrect because registers are used for immediate temporary storage during execution, not for storing the entire program and its associated data.
Write a short note on link budget analysis and its significance in satellite communication.
Write a short note on DMA (Direct Memory Access).
The magnetron generates microwaves mainly by:
A)
Velocity modulation
B)
Cyclotron resonance
C)
Space-charge effect
D)
Electron bunching in crossed fields
A magnetron is a high-power vacuum tube that functions as a microwave oscillator. It operates using 'crossed fields,' meaning an electric field (between the cathode and anode) and a magnetic field (perpendicular to the electric field) are applied simultaneously.
1. **Mechanism**: Electrons emitted from the central cathode are accelerated toward the anode. However, the perpendicular magnetic field forces them into curved, cycloidal paths.
2. **Bunching**: Due to the interaction between the electrons and the RF field of the resonant cavities in the anode, electrons form 'spokes' or bunches. This process is known as electron bunching in crossed fields.
3. **Energy Transfer**: As these bunches rotate and pass the openings of the resonant cavities, they induce high-frequency electromagnetic fields, transferring their kinetic energy to the microwave field.
Why other options are incorrect:
- **a. Velocity modulation**: This is the primary mechanism for Klystrons, where an electron beam is modulated in velocity to create bunches.
- **b. Cyclotron resonance**: While the magnetron involves circular motion, it is not a cyclotron resonance device (like a cyclotron accelerator); it relies on the interaction of the bunch with the cavity walls.
- **c. Space-charge effect**: While space charge exists in all vacuum tubes, it is not the primary mechanism for microwave generation in a magnetron.
The operating mode of 8086 after applying active low MN/MXβ is:
A)
Minimum mode
B)
Maximum mode
C)
Supervision mode
D)
User mode
The 8086 microprocessor has a pin named MN/MX' (Minimum/Maximum). This pin is used to determine the operating mode of the processor based on the logic level applied to it:
1. **Minimum Mode**: When the MN/MX' pin is tied to Vcc (Logic 1), the processor operates in Minimum Mode. In this mode, the 8086 generates all the necessary control signals (like ALE, RD, WR) itself, and it is typically used in single-processor systems.
2. **Maximum Mode**: When the MN/MX' pin is tied to Ground (Logic 0), the processor operates in Maximum Mode. The term 'active low' (indicated by the prime symbol ' or the bar over the signal) means the function is activated when the signal is at a low voltage level (0). In Maximum Mode, the 8086 requires an external bus controller (like the 8288) to generate the control signals, allowing for multi-processor configurations or co-processor integration.
Therefore, applying an active low signal to the MN/MX' pin puts the 8086 into Maximum Mode.
Write short notes on pipelining and its advantages.
How does Harvard architecture improve performance over Von Neumann architecture?
Which waveguide mode is the dominant one in a standard rectangular waveguide?
A)
TE10
B)
TE01
C)
TM10
D)
TM01
In a rectangular waveguide, the 'dominant mode' is defined as the mode with the lowest cutoff frequency. The cutoff frequency for a mode (m, n) is given by the formula: fc = (c / 2) * sqrt((m/a)^2 + (n/b)^2), where 'a' is the wider dimension and 'b' is the narrower dimension (a > b).
1. For TE modes (Transverse Electric), m and n can be 0, but not both zero. The lowest value occurs when m=1 and n=0, resulting in the TE10 mode.
2. For TM modes (Transverse Magnetic), both m and n must be at least 1 (m β₯ 1, n β₯ 1). Therefore, the lowest TM mode is TM11, which has a significantly higher cutoff frequency than TE10.
Comparing the options:
- TE10: Lowest cutoff frequency (Dominant).
- TE01: Higher cutoff frequency than TE10 because b < a.
- TM10 and TM01: These modes cannot exist in a rectangular waveguide because for TM modes, both indices must be non-zero.
Thus, TE10 is the dominant mode.