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Why 6 db is a good attenuation?
6 dB is not good nor bad as an attenuation, if the context and the signal that is attenuated is not specified. As a rule of thumb, addition between dBs is multiplication between linear attenuation, thus since 3dB is a division of the power by two, 6 dB means a division of the power by 4. Just to give an idea: In free space, without obstacles and reflections, the power of a normal voice attenuates 6 dB in dry air in about 230 cm (assuming 180° directional sound emission of the mouth, that is reasonable). This is the combined action of intrinsic air attenuation (the sound ordered power is converted by traversing air in disordered oscillations of molecules: i.e. heath) that is very small (about 1 dB/km) and of the increase of the area where the power is distributed, that going farer and farer from the source is a sphere of greater and greater radius so that power decrease due to this last effect as the square power of distance from source. The humidity further reduces air intrinsic attenuation, but since the dominant phenomenon is the other, we can say that practically nothing changes. If music is considered, the situation is more complex. Music frequencies are much more extended than voice frequencies and attenuation of the material depends on frequency (while attenuation due to distance does not, as it is intuitive). High frequencies attenuates in air much more than low frequencies, for example 50 kHz attenuates about 0.9 dB/m in dry air for 180° directional sound emission. Thus attenuation also imply a small distortion of music due to its dependence on frequency. However this effect is not so relevant to be problematic when hearing music in concert halls, due both to the small distance and to the logarithmic sensitivity characteristic of out ears. Moreover in concert halls there are a lot of reflections that are exploited in the design of a good concert hall to concentrate the sound on the public, thus the real attenuation is much reduced by the fact that power diverging from the source is redirected towards the hall center by reflections. A problem to avoid in such a design is to exploit reflections from objects too far from the source or the hall. In this case reflections recover energy, but are also delayed with respect to the original sound, creating a bad echo effect. Light exhibit similar behavior, but much more evident due to the huge frequency extension of visible light.
What is the difference between digital and analog signals?
Digital/Analog An analog or analog signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context, however mechanical, pneumatic, hydraulic, and other systems may also convey analog signals. An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge. Any information may be conveyed by an analog signal, often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure, and is achieved using a transducer. For example, in sound recording, fluctuations in air pressure (that is to say, sound) strike the diaphragm of a microphone which causes corresponding fluctuations in a voltage or the current in an electric circuit. The voltage or the current is said to be an "analog" of the sound. Since an analog signal has a theoretically infinite resolution, it will always have a higher resolution than any digital system where the resolution is in discrete steps. In practice, as analog systems become more complex, effects such as nonlinearity and noise ultimately degrade analog resolution such that digital systems surpass it. In analog systems, it is difficult to detect when such degradation occurs, but in digital systems, degradation can not only be detected but corrected as well. Disadvantage The primary disadvantage of analog signaling is that any system has noise - i.e., random variation. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically, these losses can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair. The effects of noise make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well. Even if the resolution of an analog signal is higher than a comparable digital signal, in many cases, the difference is overshadowed by the noise in the signal Digital The term digital signal is used to refer to more than one concept. It can refer to discrete-time signals that are digitized, or to the waveform signals in a digital system. Digital signals are digital representations of discrete-time signals, which are often derived from analog signals. An analog signal is a datum that changes over time-say, the temperature at a given location; the depth of a certain point in a pond; or the amplitude of the voltage at some node in a circuit that can be represented as a mathematical function, with time as the free variable (abscissa) and the signal itself as the dependent variable (ordinate). A discrete-time signal is a sampled version of an analog signal: the value of the datum is noted at fixed intervals (for example, every microsecond) rather than continuously. If individual time values of the discrete-time signal, instead of being measured precisely (which would require an infinite number of digits), are approximated to a certain precision-which, therefore, only requires a specific number of digits-then the resultant data stream is termed a digital signal. The process of approximating the precise value within a fixed number of digits, or bits, is called quantization. In conceptual summary, a digital signal is a quantized discrete-time signal; a discrete-time signal is a sampled analog signal. In the Digital Revolution, the usage of digital signals has increased significantly. Many modern media devices, especially the ones that connect with computers use digital signals to represent signals that were traditionally represented as continuous-time signals; cell phones, music and video players, personal video recorders, and digital cameras are examples. In most applications, digital signals are represented as binary numbers, so their precision of quantization is measured in bits. Suppose, for example, that we wish to measure a signal to two significant decimal digits. Since seven bits, or binary digits, can record 128 discrete values (viz., from 0 to 127), those seven bits are more than sufficient to express a range of one hundred values. Summary: Digital communication systems offer much more efficiency, better performance, and much greater the flexibility. Analog in a watch is where you have to read the numbers. Digital shows the numbers for you. a digital signal is what a computer system is based around; mainly zeros and ones / or noughts and ones as illustrated. a zero equates to zero volts approx . a one ( logic ) is 5 volts +_ a tolerance value. but there is limited range of signal in between these 2 points. a measured value of 2.5 volts would not be equal to either a logic 1 or nought . .... when a circuit / usually a transistor device switches on or off the voltage at its terminal usually changes from zero to 5 volts or logic 1 . the digital circuit only recognizes values at or around these 2 points and interprets them as a logic 1 or 0. .. in the case of the analog signal, the value could change between a negative value to positive or from zero to a positive value, within the supply constraints and still be recognized.
Difference between ofdm dsss fhss?
Orthogonal Frequency Division Multiplexing (OFDM) is a multiple-carrier (MC) modulation technique which creates frequency diversity. A high-speed data stream is converted into multiple low-speed data streams via Serial-to-Parallel (S/P) conversion. Each data stream is modulated by a subcarrier. That way, instead of having a frequency-selective fading wireless channel, where each frequency component of the signal is attenuated and phase-shifted in different amount, we have multiple flat-fading subchannels. In other words, instead of having a signal with symbol duration smaller than the channel delay (remember that high frequency means low duration because f = 1/T), we have may subsignals with duration larger than the channel delay (to simplify things, consider this: if the symbol duration is 1 s and the channel delay is 10 s, we will have interference between 10 symbols). That way, channel distortion is compensated. The OFDM symbol is the composite signal formed by the sum of the subcarriers, so the data rate is still the same as if we transmit the original high-speed signal, but as we said, the channel distortion is compensated. OFDM compensates the Inter-Symbol Interference (ISI) caused by the fact that different signals take different paths and arrive at the receiver with different delay (multipaht propagation distortion). OFDM subchannels are not separated by a guard band, but they overlap. However, they are orthogonal at the subcarrier frequencies, and that way they don't interfere with each other. We have very good utilization of the available bandwidth due to the overlapping of the subchannels. Moreover, each subcarrier can be modulated seperatelly (usually, QAM or QPSK modulation is used, depending on the channel conditions, which are measuer using channel estimation via pilot carriers). Also, we can use adaptive modulation and conding (AMC) at each subchannel in order to accomplish error-free communication with the highest data-rate possible. Due to the orthogonality principle, we don't need a bank of modulators at the transmiter and a bank of demodulators/detectors at the receiver, but simply a chip implementing the Inverse Discete Fourier Transform (IDFT) and the DFT respectively - and that can be done easy, effectively and with low-cost using a chip running the Fast Fourier Transform (FFT) algorithm. Timing errors/phase distortion must be controlled because they may create ISI between OFDM symbols and ICI (Inter-Carrier Interference) between subcarriers. We add a Cyclic Prefix (CP) to avoid ISI between OFDM symbols and synchronization methods to avoid ICI. Also, the inherent Peak-to-Average Power Ratio (PAPR) of the OFDM signal must be reduced because forces the power amplifier of the transmitter to operate on the non-linear region of its characteristic function. Spread Spectrum (SS) techniques convert a low-speed data stream into a high-speed data stream. That way, the bandwidth of the modulated carrier becomes much larger than the minimum required transmission bandwidth. This is like Frequency Modulation (FM): we trade transmission bandwidth with Signal-to-Noise (S/N) ratio, meaning that we can have error-free communication transmiting lower-power signals. The signal is spreaded in a huge bandwidth. That way, instead of having the noise (which is like an interference signal) concetrated to some symbols and corrupting the signal, the noise is uniformly distributed over the signal bandwidth. Moreover, the signal is not easilly detectable by a third-party because it is hided in the background noise. Finally, it has anti-jamming characteristics. There are two techniques to create a SS signal: Direct-Sequence Spread Spectrum (DSSS) multiplies the data stream with a high-data rate sequence called chip sequence or Pseudo-Noise (PN) sequence, because due to its lenght is seems as a random signal, like the noise (but of course, it is a completely deterministic signal; that's why we use the Greek term "Pseudo-", which means "it appears to be, but it is not"). DSSS creates time diversity (a "variety" in the time domain). Frequency-Hopping Spread Specturm (FHSS) uses a chip sequence to conrol the frequency hops of the carrier. The resulting signal is like a progressive-FM signal. FHSS creates frequency diversity (a "variety" in the frequency domain). SS techniques give a Spreading Gain (SG) to the transmitted signal, which is simillar to the Coding Gain (CG) of the error-control codes [remember: in Forward-Error Correction (FEC) techniques, we add additional bits to correct errors; we use this rendudancy for error control. That is, we increase the transmitted bandwidth but we can decrease the transmitted power required to have an acceptable S/N at the receiver). Moreover, SS techniques can be combined with multiple access techniques (patterns for multiple users access a network by sharing the common channel). With Code Division Multiple Access (CDMA) a code sequence is used to give an identity to each user, which than we will transmit a signal spreaded by a PN sequence. So, each user can use the whole available bandwidth for all the time, but users do not interfere because they are separated in the code domain. The orthogonality of the codes (of the signals) must be maintained, because otherwise we will have interference between the users. Finally, a RAKE receiver can be used to resolve the multiple paths and compensated the ISI caused due to the multipath propagation. OFDM and SS techniques can be combined (MC-CDMA). OFDM can also be combined with the Frequency Division Multiple Access (FDMA) -> OFDMA. Finally, OFDM can be combined with Multiple Input-Multiple Output (MIMO) techniques. In MIMO, we have multiple transmiting and receiving antennas. So, we have N parallel channels instead of a single channel, and this creates a signal which is N times faster (oversimplified, but basically true ...). In each channel we can use OFDM to avoid ISI and frequency-selectivity, while maintaining the high-data rate. Finally, MIMO can create diversity which enables the system to receive the best-quality signal.
What does attenuated virus vaccine consist of?
attenuated virus consist of same virus but its capacity to cause disease has deleted by the process of attenuation.
What is an attenuated peak in a storm hydrograph?
Firstly an attenuation is the reduction in the peak of a hydro-graph as it movesdownstream, resulting in a more broad, flat hydro-graph.Therefore the attenuated peak is the highest point before it attenuates.
What is animal passage and attenuation?
This is an old technique used to isolate attenuated organisms for use in vaccine development. Attenuation refers to rendering an organism (bacteria or virus) less virulent or pathogenic (less dangerous to humans). This is accomplished by infecting one animal, taking the infection from that animal to infect the next, and so on in a controlled manner. After several passages, the bacteria or virus is adapted to live in the animal host and not in humans and so can sometimes work as a vaccine. An example of this is the smallpox vaccine which was attenuated in cattle.
What are the main factors that determine the attenuation of xrays?
The main factors that determine how strongly a beam is attenuated arethe energy of the incident photons;the atomic number (Z) of the medium (absorber material);the density of the medium;as well as the thickness of the medium
Does a fluid's density change when it is compressed and attenuated?
Yes it does change because its mass does not change but its volume does. When it is compressed the density will increase because its volume does. When it is attenuated will decrease because the volume does. Density is mass over volume. Remember: it only works because its mass stays the same and the volume changes.
Is it true that 'possibility of reversion to virulence is of concern in live attenuated virus?
Yes, the possibility of reversion to virulence is a concern in live attenuated virus vaccines. Although these vaccines are weakened, there is a small chance that the virus could regain its virulence and cause disease. To mitigate this risk, vaccine developers carefully design and monitor the attenuation process.
Which types of matter can be attenuated?
None. Light and sound waves can be attenuated, but not matter.
How Attenuation measured?
RMS Output divided by input, usually expressed in deciBells. Depends on whether it is power or voltage being attenuated. Voltage, it's 20log(Vout/Vin) Power, it's 10log(Pout/Pin) The difference is because power is proportional to voltage squared.
What type of wave is absorbed by an object and may disappear?
An absorbed wave that may disappear is called an attenuated wave. Attenuation occurs when a wave loses energy as it passes through a medium or encounters obstacles, causing the wave to decrease in intensity or disappear.
What is cutoff wave number?
The cutoff wave number is the maximum wave number that can propagate in a waveguide or transmission line without attenuation or loss. Waves with wave numbers higher than the cutoff wave number will be attenuated and cannot propagate effectively. It is an important parameter in the design and analysis of waveguides and transmission lines.
Which color is LEAST attenuated in the water?
blue
Which vaccine contains weakened?
They are called attenuated vaccines. Attenuated means weakened, they do this usually with chemicals and then the attenuated viruses are not able to make you sick, but they are strong enough to trigger the immune response to provide immunity.An attenuated virus. Attenuated simply means weakened. For example, you will see references to this in regard to the flu vaccines. This is also abbreviated when talking about the flu vaccines as LAIV, Live Attenuated Influenza Vaccine.That is a good description of what a vaccine is, although some other substances also could be described similarly. The weakened or killed virus in a vaccine is non-threatening to most people. It can be a problem for infants under six months old, some children and adults with under-developed immune systems or who have immune system disorders.
