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

Reduce the number of crystals required
Increase the frequency stability of the synthesizer
Reduce the number of decades
Reduce the spurious frequency problem

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Radio Receivers
In a broadcast superheterodyne receiver, the

Local oscillator frequency is normally double the IF
Mixer input must be tuned to the signal frequency
RF amplifier normally works at 455 kHz above the carrier frequency
Local oscillator operates below the signal frequency

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