Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: Dec2014

• Independent Sideband (ISB) is an amplitude modulated technique in which a single carrier frequency is independently modulated by two different modulating signals.
• In other words, ISB is a form of double sideband transmission system in which the transmitter comprises of two independent single sideband suppressed carrier modulators. One modulator generates only the upper sideband, and the other generates only the lower sideband.
• The single sideband output signals from the two modulators are combined to form a double sideband signal in which the two sidebands are completely independent of each other, except that they are symmetrical about a common carrier frequency.
• The block diagram of ISB transmitter is shown in Fig9 below.

Fig9. Block diagram of ISB transmitter

• The two sidebands are generated independently by the two balanced modulators. The carrier is suppressed by 45 dB or more in the balanced modulator and the following filter suppresses the undesired sideband. The output from both the filters are then combined in the adder along with 26dB carrier to form low frequency ISB signal which then leaves the drive unit and enters the main transmitter.
• Its frequency is raised through mixing to remove unwanted frequencies by the output filter and the resulting RF ISB signal is then amplified to the desired level.
• ISB conserves both the transmit power and the bandwidth, since the two information signals are transmitted within the same frequency spectrum as against a single signal in traditional DSB transmission system.