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

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Radio Receivers
In a ratio detector

the circuit is the same as in a discriminator, except that the diodes are reversed
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

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Radio Receivers
In a radio receiver with simple AGC

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

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