The frequency generated by each decade in a direct frequency synthesizer is much higher than the frequency shown; this is done to

Solution (By Examveda Team)

Direct Frequency Synthesizer:
A direct frequency synthesizer is a type of frequency synthesizer that generates a desired output frequency by directly combining or mixing several frequencies from different sources.

The Problem: Spurious Frequencies
In a direct frequency synthesizer, the mixing process can create unwanted frequencies called spurious frequencies. These are frequencies other than the desired output frequency that can interfere with the intended signal.

The Solution: Higher Frequency Generation
Generating a much higher frequency than the displayed frequency in each decade helps reduce spurious frequencies. This is because the spurious frequencies are usually related to the difference or sum of the frequencies being combined. By using higher frequencies, the spurious frequencies are shifted to higher frequency ranges which are often easier to filter out. They are less likely to fall within the desired operating frequency range of the receiver or cause interference. The filtering process becomes more efficient and effective at higher frequencies.

Why other options are incorrect:
Option B: Increasing frequency stability is important, but it's not the primary reason for generating higher frequencies within each decade. Frequency stability is addressed through other design choices.
Option C: The number of decades is determined by the frequency range of the synthesizer, not by the frequency generated within each decade.
Option D: The number of crystals required depends on the synthesizer's architecture. Using higher frequencies in each decade doesn't directly reduce crystal count. Therefore, the correct answer is A.