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DTH System
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Outdoor unit: It consists of a receiving antenna, low noise amplifier & converter the receiving antenna is parabolic reflector with a horn as the active element. The horn can be directly in front of reflector, or it may use an offset feed as shown in fig. The reflector diameter may be 0.6m for 11GHz & still smaller for K &Ka bands. The low noise block consists of a low noise wide band amplifier followed by a convertor. The output of convertor consists of a signal of UHF frequency ranging from 950-1450MHz. The advantage of using UHF frequency is that a low cost coaxial cable can be used as feeder from the outdoor unit to the indoor unit. LNB cannot be kept indoor because long cable between horn & the first amplifier will cause substantial degradation of the overall noise figure of the set.



Indoor unit: The wideband signal from the LNB is fed to an RF amplifier. The amplified signal is fed to a channel selector circuit which selects the wanted band. The selected channel is down converted to a fixed IF of 70MHz by local oscillator & mixer. IF amplifier amplifies the signal which then goes to FM detector. The detector recovers original baseband signal, consisting of CVS & audio signal. These modulated signals are fed to the normal domestic TV receiver, which after due processing reproduces picture & sound. 

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9,175 questions
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