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Why is Need of vsb modulation?
It might be helpful to have a working definition of modulation before making a statement as to why it is needed. In fact, with an understanding of what modulation is, it w…ill be obvious why it is included in electronic communications. Modulation is the "message" or the "intelligence" that is impressed on a radio frequency (RF) carrier. When we transmit a signal, we generate a carrier frequency, and then we modulate it. We "add" the message or the information we wish to transmit by modulating the carrier in some way. There are at least a dozen different modulation schemes ranging from simple to real head scratchers. They either modify the amplitude, the frequency or the phase of the carrier. Let's look at a few. The simplest modulation technique is taking the transmitted signal and turning it on and off. It is "keyed" to send a series of pulses. Morse code uses on-off keying. In this method of modulation, no modification of the RF carrier signal itself is made. It is simply switched on and off. (It could be looked at as amplitude modulation with the carrier either at zero amplitude or at "maximum" amplitude with nothing in between.) A series of pulses can be transmitted. With Morse code, a short "on" period will send a dot or "dit" out. If we extend the "on" period a bit, we can send a dash or "dah" out. Nothing real sophisticated here, but basic and effective communication. There are obvious limits to how fast information can be transmitted with this modulation scheme. (But don't tell the hams who still use it!) Most of us are familiar with AM radio. AM is amplitude modulation. The amplitude of the RF carrier is modified to modulate it. The amplitude of the modulating signal will determine the amount that the amplitude of the carrier is changed. (The volume of the modulation determines how much the amplitude of the carrier is changed. The frequency of the modulating signal determines the rate of change of the amplitude of the carrier. (The frequency of the modulation determines how fast the amplitude of the carrier is changed.). The frequency of the carrier is held constant through all this. How about FM? In frequency modulation, the amplitude of the carrier is constant. It's left alone. But the frequency of the RF carrier is changed. It is swung above and below where it sits (it's assigned center frequency) at a rate proportional to the frequency of the modulating signal, and at an amount proportional to the amplitude of the modulating signal. In FM single sideband, the carrier frequency and the frequencies above the carrier are transmitted and the frequencies below the carrier are suppressed (upper sideband transmission). Or the frequencies below the carrier are transmitted with the carrier and the upper frequencies are suppressed (lower sideband transmission). In conventional television, the video signal is single sideband, suppressed carrier. It's like "regular" upper sideband transmission except the carrier signal is suppressed. Sideband transmission "saves" space on the RF spectrum. And it works because we really don't need "all" of the FM signal to demodulate the signal at the receiver. Other forms of modulation become more complex. CDMA (code division multiple access), TDMA (time division multiple access) and other methods are used in cell phones to modulate the carrier so the digital data stream can be impressed on the carrier. Modulation is the addition of intelligence to a carrier signal. It's the message. Modulation is necessary because the point of communication is getting the message through. A Simple answer: Simply this... Any communications medium: e.g. Free space - radio waves, Air - Sound waves or radio waves, Optical Fibre - Light, Copper Wires Electrical Anergy (with frequency limits of the copper wire construction) is made for a certain type of signal. But if the signal we want to send is not compatible with the medium, then it does not travel well. Modulation changes the information we want to send from it's original form, into one that is more compatable with the medium we are trying to use. For example, your computer speaks digital over a TCP/IP LAN which requires CAT 5 or better rated cables,, but to connect to your internet service provider (ISP), you need to send the signal over the wires of the telephone company (made for voice tones). To make this connection, and ADSL modem (modulator/demodulator) is used to convert the data into audio tones, which pass over the telephone line, and at the far end are converted back to digital to join the service providers network. in the reverse direct the ISP does the same, and the signals are de-modulated, back to data for your network. Or in simple terms, Its about best use of the medium. Everything else is just a away of doing it. And there are a lot of possible ways to choose.
for efficient radiation and reception the transmitting receiving antenna would have to have heights comparable to a quarter-wavelength of the frequency used .This is 75mtr for… 1mhz but at 15khz it has increased to 5000mtr .A VERTICAL ANTENNA OF THIS SIZE is unthinkable Second all sound is concentrated within the range from20 Hz to20 kHz, so that all signals from the different sources would be hopelessly and inseparably mixed up .Therefore modulation be needed.
In simple terms, modulation is required to transmit signals from variuos sources simultaneously over a common channel by means of 'multiplexing'.For ex., the bandwidth of spee…ch signals is 3.3KHz.,and transmitting N no.of speech signals simultaneously each of BW 3.3KHz causes interference.Hence,to overcome this problem, each speech signal is modulated onto one of N carriers of frequencies 60KHz,64KHz,68KHz etc... Hope u got my answer By modulation, we can reduce our antenna height as Height=1/4 wavelength and, wavelength=velocity of light/frequency
as to make the consumption of power lesser...
Modulation is the process of varying a particular characteristic(amplitude,phase,frequency) of a high frequency carrier signal according to the message signal.The need of modu…lation is as follows:- 1.Reduces the height of antenna :-The minimum height of antenna required for transmission or reception of RF signals is one forth the wavelenth i.e lower the frequency,higher the wavelenght ,greater the length of the antenna .eg.for wave of 15Khz,antenna height is 5km,which is impractical but for 1Mhz wave,height is 75 m. 2.Increases the range of communication:-At low frequencies,radiation is poor and signal gets attenuated.Modulation effectively increases the frequency of the message signal and thus signal can be transmitted over longer distance without attenuation. 3.Avoids mixing of signals and allows multiplexing of signals:-When many signals are transmitted simultaneously,they may get mixed and it becomes difficult to separate them at the receiver end.This can be avoided by modulating different signals with different carriers i.e. each signal is allocated a separate bandwidth.At the receiver end,required signal can be intercepted by the tuning the receiver to desired frenquency bandwidth.This allows multiplexing(i.e. transmission of more than one signal simultaneously over the same channel.)eg.channels on television 4.Improves the quality of reception:-Modulation techniques like frequency modulation reduce the effect of noise and improve the quality of reception.
we modulate audio signal due to following reasons: -audio is a low frequency signal that cannot travel longer distance due to low energy -if we transmit the signal without… modulation then the height of antenna will be of the order of several thousand kilometers that is impractical
OWL - Outlined White Letters: The noticeable brightness enhances the overall appearance of the tire. VSB - Vertical Serrated Band: Tastefully arranged to look good …on any vehicle.
In a radio system ... Modulation is applied to a carrier. If the carrier wasn't modulated it wouldn't carry any information other than that the transmitter was working. Not …very useful. It is the modulation which contains the "information" which we want to send.
The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a filter limit…s the frequency range to between 300 and 3400 Hz) or a limited radio frequency band.
Need of Modulation: To transfer the message signal from one site another site without any loss for that we are using modulation. Modulation classified in thre…e types. 1.Amplitude modulation. 2.Frequency Modulation. 3.Phase Modulation.
Modulation is applied to a carrier. If the carrier wasn't modulated it wouldn't carry any information other than that the transmitter was working. Not very useful. It is the… modulation which contains the "information" which we want to send.
Vestigial SideBand. It is a type of signal modulation (filtering) used in the television communication industry. It is used to help remove signal redundancy in Pulse Amplitude… Modulated (PAM) signals. Also look up 8VSB and A-VSB which are variants of VSB.