What is Modulation? Amplitude Modulation (AM),Frequency Modulation (FM),Phase Modulation (PM)
Modulation is the use of one electrical signal to “control” a primary variable of another. For example, if an audio signal voltage is used to control the “amplitude” of a carrier signal, the result is amplitude modulation.
HDMI Encoder Modulator,16in1 Digital Headend, HD RF Modulator at Soukacatv.com It is important that you do not confuse “mixing” with “modulation.” Mixing occurs when two (or more) signals are simply combined in a linear network. Modulation, however, requires one signal to “control” a variable of another; variables such as the amplitude of an RF signal [amplitude modulation (AM)], the frequency [frequency modulation (FM)], the pulse width [pulse width modulation (PWM)], the phase [phase modulation (PM)], or the pulse code [pulse code modulation (PCM)]. Unfortunately, the electronics industry has traditionally retained many circuit names that are incorrect in this regard. For instance, when you examine the actual circuit operation of many circuits labeled as a “mixer/oscillator,” you will discover that it is really a “modulator/oscillator.” Strictly speaking, when two signals are mixed, they combine without the creation of any additional frequencies. When two signals are modulated, they are said to “beat” with each other, creating additional frequencies called “beat frequencies.” If the two modulated signals are sinusoidal, the beat frequencies will be the sum and the difference of the original frequencies. AM radio broadcast transmissions contain two signals of primary importance to the user: the carrier signal and the audio signal, or the program signal. The carrier frequency is the frequency to which the radio receiver is tuned for station selection. For example, the AM radio band (also referred to as the medium-wave broadcast band, or simply the broadcast band) is legally designated from 535 to 1605 kHz. If your favorite local