Radio Receivers
The controlled oscillator synthesizer is sometimes preferred over the direct one because

It is a simpler piece of equipment
It is relatively free of spurious frequency
It does not require crystal oscillator
Its frequency stability is better

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Radio Receivers
If a FET is used as the first AF amplifier in a transistor receiver, this will have the effect of

Improving the selectivity of the receiver
Reducing the effect of noise at low modulation depths
Improving the effectiveness of the AGC
Reducing the effect of negative-peak clipping

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