baseband and bandpass signal pdf download , BASEBAND AND PASSBAND SIGNALS
As discussed earlier, the message signal generated from the information source is known as baseband signal. This baseband signal may be a combination of two or more message signals. If the baseband signal is transmitted directly, then it is known as baseband transmission. This means that the baseband
transmission does not used modulators and demodulators. The baseband signal may be both analog as well as digital.
The analog baseband signal varies continuously with time and has continuous amplitude. The digital baseband signal is discrete in both time and amplitude.
The baseband transmission is preferred at low frequencies and for short distances. However, Intersymbol Interference (ISI)* is the major problem associated with the baseband transmission.
Now, if the modulated signal is transmitted over the channel, it is known as band pass or simply passband transmission. Whenever a modulating signal is impressed upon a carrier, the modulated signal is produced. This modulated signal has fixed band of frequencies around carrier frequency. In fact, the nature of such a signal is band pass type. Therefore, modulated signals are known as passband or bandpass signals. As an example, if a 1 kHz modulating signal is impressed upon a 100 kHz carrier signal by using amplitude modulation technique then two sidebands will be generated. Lower sideband will be at
(100 — 1) i.e., 99 kHz and upper sideband will be at (100 + 1) i.e., 101 kHz.
Thus, the amplitude modulated signal will have frequencies from 99 kHz to 101 kHz. These frequencies are bandpass type. This means that the modulated signals are also bandpass i.e., passband type.
It may be noted that the bandpass transmission is generally used at high frequencies and for long distances. All television and satellite transmission are bandpass type. The bandpass transmission may be both analog and digital. If the digital signal modulates the carrier, then it is known as digital passband transmission.