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
The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency

To help the image frequency rejection
Because otherwise an intermediate frequency could not be produced
To allow adequate frequency coverage without switching
To permit easier tracking

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Radio Receivers
In a ratio detector

the linearity is worse than in phase discriminator
the output is twice that obtainable from a similar 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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Radio Receivers
In a radio receiver with simple AGC

An increase in signal strength produces more AGC
The highest AGC voltage is produced
The faster the AGC time constant the more accurate the output
The audio stage gain is normally controlled by the AGC

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