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Independent Side Band transmission uses two side bands which are independed to each other. As shown in the block diagram.
- ISB essentially consists of two SSB channels added to form two side bands around the reduced carrier. Each side band is quite independent of the other. It can simultaneouly convey totally different transmission.
- Each 100 Hz - 6 KHz channel is fed to its own balanced modulator, each modulator also receiving the output of the 100 KHz crystal oscillator. Each modulator modulates each message (100 Hz to 6 KHz) on the frequency 100 KHz.
- The USB filter and LSB filter suppresses the unwanted side band in such a way that one filter suppresses the lower side band and the other filter suppresses the upper side band respectively.
USB = 100.1 - 106 KHz
LSB = 94 - 99.9 KHz
- Both outputs are added at the hybrid adder with the 10% reduced carrier.
- The output is then fed to the balanced mier where it is mix with the output of the crystal oscillator, the frequency is then raised to 28.1 MHz +- 6 KHz.
- The resulting RF ISB signal is then amplified by the linear amplifier, until it reaches the ultimate level then is fed to teh antenna for transmission.