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

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Radio Receivers
In a ratio detector

the output is twice that obtainable from a similar phase discriminator
the linearity is worse than in phase discriminator
stabilization against signal strength variations is provided
the circuit is the same as in a discriminator, except that the diodes are reversed

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