1. (A) DEFINE APOGEE AND PERIGEE ?
ANS. :
Apogee: Apogee refers to the point in an object's orbit where it is farthest away from the Earth. In the case of satellites or spacecraft, apogee is the highest point in their elliptical orbit around the Earth. At apogee, the object is at its maximum distance from the Earth's surface.
Perigee: Perigee, on the other hand, refers to the point in an object's orbit where it is closest to the Earth. It is the lowest point in the object's elliptical orbit. Satellites or spacecraft at perigee are at their closest proximity to the Earth's surface
(B) WHAT IS THE DIFFERENCE BETWEEN LEO AND GEO SATELITE ?
LEO and GEO are abbreviations for two different types of satellite orbits:
LEO (Low Earth Orbit): Low Earth Orbit is a type of satellite orbit that is relatively close to the Earth's surface, typically ranging from a few hundred kilometers to about 2,000 kilometers in altitude. Satellites in LEO orbit the Earth at high speeds, completing an orbit in a relatively short period of time, often within 90 minutes or less. LEO satellites are used for various purposes such as Earth observation, communication, scientific research, and satellite constellations. Examples of LEO satellites include the International Space Station (ISS) and satellite constellations like SpaceX's Starlink.
GEO (Geostationary Orbit): Geostationary Orbit is a type of satellite orbit located much farther from the Earth's surface, at an altitude of approximately 35,786 kilometers. Satellites in GEO orbit have an orbital period that matches the Earth's rotation, resulting in the satellite appearing to be stationary when observed from the Earth's surface. This characteristic is particularly advantageous for communication satellites as they can maintain a fixed position relative to the Earth, allowing for continuous coverage over a specific region. GEO satellites are commonly used for television broadcasting, telecommunications, weather monitoring, and other applications that require a stable and constant connection. Examples of GEO satellites include those used for direct broadcasting satellite (DBS) services and weather satellites like GOES.
In summary, the key differences between LEO and GEO satellites are their altitudes, orbital speeds, and applications. LEO satellites are located at lower altitudes, move at higher speeds, and are typically used for applications that require frequent coverage of different parts of the Earth's surface. GEO satellites, on the other hand, are positioned at a much higher altitude, move at the same rotational speed as the Earth, and are commonly used for applications that require continuous coverage over a specific region.
(C) WHAT IS INTERMODAL DISPERSION ?
Dispersion caused by multipath propagation of light energy is referred to as intermodal dispersion. Signal degradation occurs due to different values of group delay for each individual mode at a single frequency. In digital transmission, we use light pulse to transmit bit 1 and no pulse for bit 0.
(D) WHAT IS ACCEPTANCE ANGLE DISCUSS ITS IMPORTANCE ?
The acceptance angle is determined by the numerical aperture (NA) of the optical system, which is a measure of the light-gathering ability of the system. A higher numerical aperture corresponds to a larger acceptance angle and indicates that the system can accept light rays over a wider range of incident angles.
The importance of the acceptance angle lies in its relationship to the efficiency and performance of the optical system. Here are a few key points to consider:
Light Gathering: The acceptance angle determines the range of incident angles at which the optical system can gather and accept light. A larger acceptance angle allows for a broader range of light rays to enter the system, capturing more light and maximizing the amount of information or energy that can be transmitted.
Transmission Efficiency: When light enters an optical fiber or system at an angle greater than the acceptance angle, it experiences increased losses due to increased reflection or refraction. The acceptance angle ensures that most of the incident light can be efficiently transmitted through the system with minimal losses, maintaining the overall transmission efficiency.
Alignment and Connectivity: In practical applications, such as connecting optical fibers or aligning optical components, the acceptance angle plays a crucial role. When coupling two optical fibers, for instance, the acceptance angles of both fibers must align to ensure efficient light transmission. Deviations in the acceptance angles can result in misalignment, increased losses, and reduced performance.
System Design: The acceptance angle is a parameter that optical system designers consider when designing optical devices or systems. It helps determine the appropriate numerical aperture, fiber diameter, or lens specifications to achieve the desired performance characteristics, such as transmission capacity, signal quality, or optical resolution.
In summary, the acceptance angle is important in optics and fiber optics as it governs the range of incident angles at which an optical system can accept light and maintain efficient transmission. Understanding and optimizing the acceptance angle is crucial for achieving high-performance optical systems, maximizing light-gathering capabilities, and ensuring proper alignment and connectivity in optical setups.
E.COMPARE PROBABLITY OF ERROR ASK AND BPSK MODULATION TECHNIQUE?
Probability of error is an important metric used to evaluate the performance of different modulation techniques in communication systems. Let's compare the probability of error for ASK (Amplitude Shift Keying) and BPSK (Binary Phase Shift Keying) modulation techniques.
ASK (Amplitude Shift Keying):
ASK is a modulation technique where the amplitude of the carrier signal is varied to represent digital information. In ASK, different amplitudes represent different symbols. The probability of error in ASK depends on factors such as noise, interference, and the number of levels used.
BPSK (Binary Phase Shift Keying):
BPSK is a modulation technique that uses the phase of the carrier signal to represent digital information. It transmits one bit per symbol, where a phase shift of 0 degrees represents one bit value (e.g., 0), and a phase shift of 180 degrees represents the other bit value (e.g., 1). The probability of error in BPSK is affected by noise, interference, and the modulation scheme's inherent sensitivity to phase errors.
In terms of probability of error, BPSK generally outperforms ASK. This is primarily because BPSK is less susceptible to amplitude variations caused by noise or channel impairments. BPSK relies on phase shifts, which are more robust against amplitude variations than amplitude-based modulation schemes like ASK. As a result, BPSK can achieve better error performance, especially in channels with high noise levels.
In practice, various factors, such as the signal-to-noise ratio (SNR), channel conditions, modulation scheme implementation, and the presence of other impairments, can influence the actual probability of error for both ASK and BPSK. However, when comparing the two modulation techniques in general, BPSK tends to provide better error performance due to its inherent resistance to amplitude variations.
F. STATE THE SAMPLING THEOREM ?
The Sampling Theorem, also known as the Nyquist-Shannon Sampling Theorem, is a fundamental concept in digital signal processing and communication theory. It establishes the minimum sampling rate required to accurately reconstruct a continuous-time signal from its sampled version. The theorem states:
A continuous-time signal with a bandwidth limited to B hertz can be perfectly reconstructed from its samples if it is sampled at a rate greater than or equal to 2B samples per second.
In other words, to avoid distortion or loss of information, the sampling rate must be at least twice the highest frequency component present in the signal. This condition is commonly known as the Nyquist rate.
If the sampling rate is below the Nyquist rate, a phenomenon called aliasing occurs. Aliasing causes higher frequency components of the signal to fold back into the lower frequency range, leading to the loss of information and potential distortion in the reconstructed signal.
The Sampling Theorem is of utmost importance in digital signal processing, audio and image processing, telecommunications, and other fields where analog signals are converted into digital form for processing, storage, and transmission. Adhering to the Nyquist rate ensures that the reconstructed signal closely resembles the original continuous-time signal and minimizes the introduction of artifacts or errors during the sampling process.
G. WHAT IS ALIASING EFFECT HOW CAN IT BE REDUCE?
Aliasing is an undesirable effect that occurs when a continuous-time signal is improperly sampled at a rate below the Nyquist rate, leading to distortion and the loss of information. It manifests as false or spurious frequencies in the reconstructed signal. To reduce or eliminate aliasing, the following approaches can be employed:
Increase the Sampling Rate: One straightforward solution is to increase the sampling rate above the Nyquist rate. By sampling the signal more frequently, the higher frequency components can be accurately captured and reconstructed. This approach is often used when capturing and digitizing analog signals.
Apply Anti-Aliasing Filtering: Before sampling, an anti-aliasing filter is used to remove or attenuate the frequency components above the Nyquist frequency. The filter acts as a low-pass filter, allowing only the frequencies within the desired band to pass through. This prevents high-frequency components from aliasing and folding back into the lower frequency range.
Bandlimiting the Signal: Prior to sampling, if the original continuous-time signal has a known bandwidth, it can be bandlimited to ensure that no frequency components beyond the Nyquist frequency are present. This can be done using analog filters or digital signal processing techniques. By restricting the signal's bandwidth, aliasing can be avoided or minimized.
Oversampling and Digital Filtering: Oversampling involves sampling the signal at a rate significantly higher than the Nyquist rate. After oversampling, digital filtering techniques, such as interpolation and decimation, can be applied to remove unwanted frequency components and reduce the effects of aliasing.
Use of Advanced Sampling Techniques: In some cases, more advanced sampling techniques, such as adaptive or variable-rate sampling, may be employed to address specific aliasing issues. These techniques dynamically adjust the sampling rate based on the characteristics of the input signal to mitigate aliasing effects.
It's important to note that while these techniques can help reduce aliasing, they may introduce trade-offs in terms of computational complexity, storage requirements, or system performance. The choice of the most appropriate technique depends on the specific application and the trade-offs that can be made.
H. MENTION THE USES OF A LIMITER AND DISCRIMINATOR IN FM DEMODULATION ?
In FM (Frequency Modulation) demodulation, limiters and discriminators are important components used to extract the original baseband signal from the FM modulated carrier wave. Here are the uses of limiters and discriminators in FM demodulation:
Limiter: A limiter is a non-linear circuit that limits the amplitude variations of the FM signal. It is primarily used to combat the effects of amplitude variations caused by noise and interference. The main uses of a limiter in FM demodulation are:
a. Amplitude Equalization: A limiter ensures that all frequency components of the FM signal have approximately the same amplitude. This equalization allows for a more accurate demodulation process since it eliminates the dependence of demodulation on signal amplitude variations.
b. Noise and Interference Rejection: By limiting the amplitude of the FM signal, a limiter suppresses the amplitude fluctuations caused by noise and interference. This suppression helps to improve the demodulated signal quality by reducing the impact of external disturbances.
Discriminator: A discriminator is a key component in FM demodulation that converts frequency variations of the FM signal into corresponding voltage variations. It is designed to detect and measure the instantaneous frequency of the FM signal. The primary uses of a discriminator in FM demodulation include:
a. Frequency-to-Voltage Conversion: A discriminator converts the frequency variations of the FM signal into voltage variations. The output voltage of the discriminator represents the original modulating signal.
b. Demodulation Accuracy: The discriminator provides accurate demodulation by accurately detecting the instantaneous frequency deviations in the FM signal. This allows for the recovery of the original baseband signal.
c. Linearity Improvement: Discriminators are designed to exhibit linear response over a wide range of frequency variations. This linearity ensures that the demodulated signal faithfully represents the original modulating signal.
d. Noise Immunity: Discriminators are less sensitive to amplitude variations and noise than amplitude-based demodulation techniques. This makes them more robust in the presence of noise, resulting in improved signal quality.
Together, the limiter and discriminator play crucial roles in FM demodulation by equalizing the amplitude variations, extracting the baseband signal accurately, improving noise immunity, and providing a faithful representation of the original modulating signal.