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A bandpass signal, xc(t), is a signal whose one-sided energy spectrum is both:
1) centered at a non-zero frequency, fC, and 2) does not extend in frequency to zero (DC).
The two sided transmission bandwidth of a signal is typically denoted by BT Hertz so that
the one-sided spectrum of the bandpass signal is zero except in [fC − BT /2,fC + BT /2]. This
implies that a bandpass signal satisfies the following constraint: BT /2 < fC. Fig. 1.1 shows a
typical bandpass spectrum. Since a bandpass signal, xc(t), is a physically realizable signal it is
real valued and consequently the energy spectrum will always be symmetric around f = 0. The
relative sizes of BT and fC are not important, only that the spectrum takes negligible values
around DC. In telephone modem communications this region of negligible spectral values is only
about 300Hz while in satellite communications it can be many Gigahertz.
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Role of modulation in signal transmission is varying why?
The Role of modulation in signal transmission varies because of what type of signal should be modulated.Then how long it should be travel in air.All these points are considered, when we go before modulation.Suppose we are transmitting vedio signal means it should be only Amplitude Modulated signal.If we transmitting audio signal means it should be Frequency Modulated Signals.So the Role of the modulation is varies in signal transmission.
Mixer circuit used in Amplitude demodulation?
The mixer circuit in a superhetrodyne receiver, used for both AM and FM receivers, is a local oscillator that is tuned to 455 KHz away from the desired signal (AM), or 10.7 MHz away from the signal (FM), followed by a broad band summing amplifier or, more typically, just a pair of diodes, resulting in shifting the RF signal into the IF range. By Fourier analysis, when you add two signals, you get four results, each signal, their sum, and their difference. The IF strip following the mixer, a steep skirt bandpass filter, is tuned to the difference, providing the selectivity necessary for good reception.The preceding RF stage is a semi broad band, partially tuned, bandpass tank/amplifier circuit that simply enhances the input signal, providing sensitivity instead of selectivity.
Advantages of intermediate frequency?
The intermediate frequency, or IF, in a superhetrodyne receiver is used to tune the desired signal. The IF stage is tuned to a specific, fixed frequency, usually 455 kHz for AM and 10.7 MHz for FM. Since the IF stage does not need to be adjustable, it can be designed for high performance, tight bandpass operation. This is far easier to do than creating an adjustable RF stage with tight bandpass operation. Instead, the RF stage is broadband and the IF stage is narrow band. The actual tuning of the receiver is done by varying the local oscillator that is mixed with the radio frequency (RF) signal just upstream of the IF stage. The difference frequency of the output of the mixer is then amplified by the IF stage. The audio information, to be fed to an amplifier and be heard on the speaker, is extracted after the last IF stage - either by a detector in AM or discriminator in FM.
How do you filter rf signals that distort television reception from a rooftop antenna?
There are a number of steps that you can take to prevent this distortion from occuring. But in order for you to know what to do, you should specify a few things, first: a) Do you have an antenna signal amplifier? b) Is it just one or two channels being affected, or is it all of your channels being affected? c) What channels and ranges does your antenna receive? d) What sort of distortion is it? Are adjacent channels bleeding into this one? Are there horizontal streaks and lines appearing? Or is it just an entire screen filled with noise? If all of your channels are affected or wiped out and you have an antenna signal amplifier, it may be that your amplifier's transmitted signal is too strong. Also, it could be interference from an adjacent channel or the FM band. In this case, you may need a bandpass or a bandstop filter. To get a bandpass or bandstop filter, you should probably turn to an electronics provider like Tin Lee Electronics (www.tinlee.com). You can also contact them about your problem and they should be able to help you solve it. In any case, if you could specify the above information, it would be much easier to find an answer to your problem.
What is the frequncy range of digital signal?
Telephone bandpass is 300Hz to 3000Hz. This is adequate for a recognizable and understandable voice, however the lack of high frequencies makes some people sound different on the phone.Local calls often have a slightly wider bandpass, but long distance calls are sharply filtered to cutoff at exactly 3000Hz, to avoid spillover into adjacent channels during the process of frequency division multiplexing so that many voice connections may be sent on one line (e.g. twisted pair, microwave link, optical fiber) at the same time.
