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a mixer is used to mutiply two signals with freq. say fn,fm and its output has harmonic k1*fn+k2*fm or k1*fn-k2*fm , it depends on the non-linearity c/c's of active elements,when fn is the carrier freq. fc and the other signal is ur signal to be transmitted then the output is the modulated signal , this is AM modulation as u get the same envelope of ur signal but varying with the carrier freq.
while the modulator is a general notation for a device that modulate the signal and can be AM ,FM or any other kind of modulation "can also be digitalsuch as PCM ,PWM ,.....etc"
* Frequency mixer, a telecommunications device for deriving useful signals from modulated carrier waves
* Audio mixing console, an electronic device for combining, routing, and changing the level, tone, and/or dynamics of two or more audio signals
* Vision mixer, a European term for an electronic device for combining of two or more video signals; known in the US as a production switcher
* Mode mixer, a telecommunications device for handling signals on optical fibers
Modulation is the process of varying a carrier signal in order to use that signal to convey information. The three key parameters of a sinusoid are its amplitude, its phase and its frequency, all of which can be modified in accordance with an information signal to obtain the modulated signal. There are several reasons to modulate a signal before transmission in a medium. These include the ability of different users sharing a medium (multiple access), and making the signal properties physically compatible with the propagation medium. A device that performs modulation is known as a modulator and a device that performs the inverse operation of demodulation is known as a demodulator. A device that can do both operations is a modem (a contraction of the two terms).
In digital modulation, the changes in the signal are chosen from a fixed list (the modulation alphabet) each entry of which conveys a different possible piece of information (a symbol). The alphabet is often conveniently represented on a constellation diagram.
In analog modulation, the change is applied continuously in response to the data signal. The modulation may be applied to various aspects of the signal as the lists below indicate.
Modulation is generally performed to overcome signal transmission issues such as to allow
* Easy (low loss, low dispersion) propagation as electromagnetic waves
* Multiplexing — the transmission of multiple data signals in one frequency band, on different carrier frequencies.
* Smaller, more directional antennas
Carrier signals are usually high frequency electromagnetic waves.