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An equivalent baseband signal or equivalent lowpass signal is a complex valued representation of the modulated physical signal (the so-called passband signal or RF signal). It is a concept within analog and digital modulation methods for (passband) signals with constant or varying carrier frequency (for example ASK, PSK QAM, and FSK).
A significant condition could be an electric current (voltage, or power level), an optical power level, a phase value, or a particular frequency or wavelength. The duration of a significant condition is the time interval between successive significant instants. [3] A change from one significant condition to another is called a signal transition.
The passband of a receiver is the range of frequencies it can receive when it is tuned into the desired frequency (channel). A bandpass-filtered signal (that is, a signal with energy only in a passband), is known as a bandpass signal, in contrast to a baseband signal. [1] The bandpass filter usually has two band-stop filters.
The resulting so called equivalent lowpass signal or equivalent baseband signal is a complex-valued representation of the real-valued modulated physical signal (the so-called passband signal or RF signal). These are the general steps used by the modulator to transmit data:
It may refer more specifically to two subcategories: Passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter, a communication channel, or a signal spectrum. Baseband bandwidth is equal to the upper cutoff frequency of a low-pass filter or baseband signal, which includes a zero ...
According to the most common definition of a digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion.
Analog transmission can be conveyed in many different fashions: Optical fiber; Twisted pair or coaxial cable; Radio; Underwater acoustic communication; There are two basic kinds of analog transmission, both based on how they modulate data to combine an input signal with a carrier signal.
If the information to be transmitted (i.e., the baseband signal) is () and the sinusoidal carrier is () = (), where f c is the carrier's base frequency, and A c is the carrier's amplitude, the modulator combines the carrier with the baseband data signal to get the transmitted signal: [4] [citation needed]