Subject: Priniciples of Communication Engineering

Difficulty : Medium

Marks : 05

• Stringent frequency response requirements on side band filter in SSB can be related by allowing a part of unwanted side band ( called vestige ) to appear in the output of modulator.
• To generate VSB signal we generate DSB-SC signal and pass it through side band filter. This filter will pass wanted signal side band.

• VSB signal at the output is applied to chain of linear amplifiers. Then it is given to power amplifiers to raise the power level.

  

• In TV transmission it is necessary to transmit video and audio information simultaneously.

• The BW of video signal is about 4.2 MHz. So if we use DSBFC i.e. AM transmission than BW required will be 4.2 x 2 = 8.4 MHz.
• If guard band is inserted between sound and picture carriers and inter channel guard band then BW is 9 MHz (approx) which is very large.
• In VSB upper side band of video signal and picture carrier are transmitted without suppression.
• Vestige or part of lower side band is transmitted. First 1.25 MHZ of lower side band is sent,So total BW of 6 MHZ instead of 9 MHZ is required.